Lathraea squamaria

When it comes to parasites, for most people it is a case of "out of sight, out of mind", and that especially applies to holoparasitic plants that spend most of their lives hidden underground or inside the tissue of their host plant, and only make their presence known when their flowers emerge from the ground or their host. Lathraea squamaria is a parasitic plant that infects many different types of deciduous trees including beech, hazel, aspen, and ash. Also known as the common toothwort, it is found in ravine forests and spends most of its life underground as rhizomes clinging to the roots of its host.

Left: A whole Lathraea squamaria plant, Centre: L. squamaria flowers in bloom, Right: Cross-section of a L. squamaria fruit with developing seeds.
Photos from Fig. 1, Fig. 3, and Fig. 5 of the paper.

While the word "parasite" often has a negative connotation, there are many parasites that perform important ecosystem services, and L. squamaria is no different. When few other plants are flowering, the toothwort blooms, providing bees with an important early-season food source when food for such pollinators are relatively scarce. They also release nutrient-rich saps that are savoured by small invertebrates and other plants in the forest.  While common toothwort has been studied for almost two centuries, because it exists almost entirely underground, many of the most basic aspects of this plant's biology and structure remain a mystery.

This post features a study where researchers set out to provide a detailed description of this parasite, particularly the haustoria, a very important part of parasitic plant as this is the organ they use to cling to and dig into their host. They collected L. squamaria from parts of the Czech Republic and Ukraine, sampling toothworts at different stages of development, from newly sprouted rhizomes to fully matured fruiting plants. Throughout the toothwort's life, the only part of this parasite which emerges aboveground are its flowers, which are mainly pollinated by specialised bees that can tolerate the parasite's extremely alkaline nectar. While the nectar of most flowers is generally slightly acidic, nectar from the common toothwort has a pH level of 11.5, which is comparable to soap.

As with other plants, once they are pollinated and produce mature fruit, they need to disperse their seeds, and like other holoparasitic plants, its seeds are transported by ants. Lathraea squamaria recruits their service by providing them with a treat, in the form of a tiny tag on each seed called an elaisome. This fleshy tag is irresistible to ants, which carries the whole seed back to its nest to rip off this tasty morsel. The ant then tosses the seed into the nest's communal refuse pile, but by doing so, they also end up planting the seed where it can sprout and find a new host.

The seed begin sprouting when exposed to chemicals which are extruded by the host tree's roots, and when the toothworth initially emerges from its seed as a rhizome, it can extend itself quite a long way beneath the ground in search for a host, before latching itself around the roots of a tree. Once it does, it sends out fine tendrils that tap into the host's vascular system, not just to draw nutrients, but also to send proteins, hormones, and signalling molecules to the host plant to make it more compliant. But sometimes they can also get a bit too overzealous and end up wrapping those tendrils around their fellow parasites, or even themselves. This has also been observed in other parasitic plants.

While called the "common" toothwort, researchers have found that they're not found in just any ravine forest, but mostly in mature forests which have not been disturbed. This is comparable to some horsehair worms which help keep trout well-fed with drowning crickets - some of these worms are only found in old growth forests. While one is a plant and the other a worm, both of those parasite provide important ecosystem services. For all that those parasites may take from their hosts, their actions also help support many other inhabitants of such forests.

Reference:

Krasylenko, Y., Teixeira-Costa, L., Sosnovsky, Y., Šamajová, O., Ovečka, M., Sytschak, Horielov, O., Brücknerová, N., Polláková, K.  & Ioannou, E. (2026). Persephone’s Flower: Morphology and anatomy across the life cycle of the forest root holoparasite Lathraea squamaria (Orobanchaceae). Flora 337: 152948.

Cynomorium songaricum

Deserts can be challenging environments to live in, doubly so when you are a parasitic plant that has to latch onto the roots of a specific host plant to live. Cynomorium songaricum is an endangered holoparasitic plant living in the deserts of northwest China, and it parasitises nitre bushes. Nitre bushes are known for their edible, slightly salty fruits, but C. songaricum is also prized for its culinary and medicinal value. In China, the fruits of this holoparasitic plant are known as "锁阳" and are used in traditional Chinese medicine.

Top left: A Cynomorium songaricum plant, Top right: Ants on the stem of a C. songaricum plant, Bottom left: Beetles feeding on the stem of a C. songaricum plant, Bottom right: C. songaricum seeds collected from the nest of Messor desertora ants.
Photos from Fig. 1 and 4 of the paper.

Despite its important cultural value, as is often the case with parasitic plants, very little is known about its ecology or how it propagates. Cynomorium songaricum is a root parasite, which means its dust-like seeds have to either come in contact with or at least be very close to its host's roots in order to germinate. And the roots of its host are located about three metres underground beneath the dry desert sand - so how do C. songaricum's tiny seeds reach all the way down there?

To find out, scientists from Inner Mongolia University conducted a series of studies in the eastern part of the Tengger Desert and the Badain Jaran Desert in Inner Mongolia. Over multiple days, these scientists observed the C. songaricum plants on rotating shifts during daytime and throughout the night, and when it got too cold at night to observe the holoparasites in person, remote cameras were used to keep an eye on the activities around the plants. They also collected samples from some of those plants, which were used for feeding experiments involving C. songaricum seeds and various insects. 

Like many other holoparasitic plants, C. songaricum has stinky flowers that attract flies to serve as pollinators. But when it comes to its seeds, it offers up something sweeter, which makes them attractive to hungry desert insects. And the main customers for what C. songaricum's offerings seems to be beetles and ants. The beetles eat the pulpy material around the seeds and then poop the seeds out after a day or two, which are then buried by wind. That way of reaching the host plant is a bit hit-or-miss since there's no guarantee that the seeds would be buried anywhere near the host plant's roots. But beetles are messy eaters, and in the process, they also drop some of the seeds onto the desert sand. 

That's when C. songaricum solicits help from another common desert insect. Each seed has a little fleshy tag on it called an elaisome, and it turns out this little tag attracts the attention of desert ants, which considers the elaisome to be a tasty snack. So as with all things the ants find tasty, they haul the seeds back to the larder of their nest, which works out exactly in C. sonagrisum's favour. Because it just so happens that those ants often make their homes around nitre bushes, and these nests can extend up to three metres underground - placing them right on the same level as the nitre bush's roots. So by taking the C. songaricum seeds back to the nest, the ants also inadvertently plant them in the strike zone of the host plant's roots

So that's how a parasitic plant is able to disperse its seeds across a wide, sandy desert - with the help of some little friends. To most observers, a desert may seem empty and barren. But if you take a closer look, you will find that it can be a place which is full of life and connections. 

Reference:

Wang, Z., Guan, H., Li, B., Zhang, Q., Chen, Q., Wang, D., He, K., Jin, Z., & Chen, G. (2025). Endozoochory by the cooperation between beetles and ants in the holoparasitic plant Cynomorium songaricum in the deserts of Northwest China. PloS One, 20: e0319087.

Lysiana exocarpi

Sometimes parasites get their own parasites too, and if you think that "enemy of my enemy is my friend", then you'd think this would be good news for the host. But that depends on the host-parasite pairings in question. This post is about a study on mistletoes, a plant that many people associate with Christmas celebrations, but they are also parasitic plants, specifically, they are "hemiparasites" - which are plants that can do their own photosynthesis, but they draw water and other nutrients from a host plant.

Left: A harlequin mistletoe attached to a box mistletoe (red arrow indicating attachment point), Right: Close-up of the attachment point (indicated by red arrow) between a harlequin mistletoe and box mistletoe.
From Fig. 1 of the paper

Mistletoes have varying degrees of host specificity, with some of them parasitising only a selected handful of trees and shrubs species, while others can infect a wide range of different plants. They parasitise their host using a modified root called haustorium, which bores into the host plant's stem, tapping into its flow of water and nutrients. But sometimes, mistletoes find themselves on the receiving end of a haustorium from another mistletoe. After all, mistletoes are just another type of plant. Parasitic plants that engage in such a lifestyle are called "epiparasites" by botanists, though they also fall under the larger umbrella of hyperparasites - parasites of parasites.

The Australian harlequin mistletoe (Lysiana exocarpi) is a very versatile hemiparasite - it can infect over a hundred different plant species and when the opportunity arises, it parasitises a fellow mistletoe, namely the box mistletoe (Amyema miquelii). One of the challenges for an epiparasite is maintaining a lower water potential than its host. Water has a tendency to move from areas of high concentration to lower concentration, and in plants, this is how water is transported from the roots to the shoots/leaves because the atmosphere (where the shoots/leaves are) have lower water concentration than the soil (where the roots are). As water diffuses into the atmosphere from the leaves, it draws more water from the roots to the shoots.

So in order to suck up water from its host, a mistletoe would need to maintain a lower water potential than the shoots of the host tree - this is why mistletoes are very thirsty plants. And an epiparasite parasitising another mistletoe would need to maintain an even lower water potential to ensure water would flow to it through both its host mistletoe as well as the tree that its host mistletoe is parasitising. So when a mistletoe is parasitising another parasitic plant, it would need to change certain aspects of its physiology.

This study took place at the Onkaparinga River National Park in South Australia, in a woodland composed mostly of pink gum (Eucalyptus fasciculosa). The researchers conducted a variety of measurements on both host trees and mistletoes, and collected samples of their leaves. What they found was that when the harlequin mistletoe is parasitising another mistletoe, it opened up more of the stomata on its leaves, so water is released into the atmosphere at a higher rate. At the same time, it also grew leaves with larger surface area, and had higher concentration of potassium and magnesium in them. All this decreases the mistletoe's water potential, which means the harlequin mistletoe gets more thirsty when it's parasitising another mistletoe. 

But what happens to its host mistletoe? Well, surprisingly enough, it seems that the box mistletoe doesn't suffer from being parasitised. It compensates for the cost of its thirsty epiparasite by simply drawing even more resources from its eucalyptus host, essentially outsourcing the cost of hosting a harlequin mistletoe to the tree. All this means that the host tree ends up taking the full brunt of BOTH parasites. Eucalyptus trees which are host to a parasitised box mistletoe have stiffer leaves than if it is parasitised by the box mistletoe alone. Among eucalyptus, growing stiffer leaves is often a symptom of nutrient and water deprivation, which is perhaps not surprising since the tree is hosting a pair of very thirsty plants, and this can have long term impacts on its growth and reproduction.

So at least when it comes to parasitic plants, the enemy of your enemy is not necessarily your friend, in fact, you might end up paying the price for their antagonistic relationship.

Reference:

Scalon, M. C., & Rossatto, D. R. (2024). Challenging the 'Immunity Hypothesis': Primary or Secondary Parasitism as Different Survival Strategies for the Harlequin Mistletoe Lysiana exocarpi (Behr) Tiegh. Flora 323:152662.

Epifagus virginiana

Epifagus virginiana is a parasitic plant that grows on the roots of American beech trees. Also known as "beechdrops", clumps of their brown stems can be found protruding from the forest floor, reaching up to 30 cm tall and lined with purple-white flowers. To most people, they look like just another ordinary plant amidst the undergrowth. But Epifagus lacks a key component which is usually a defining characteristic of plants - chlorophyll, the pigment which allows plants to harness solar power. Instead, the way this plant obtains its nutrients is via an underground tuber attached to the roots of its host. The beechdrop is a very discerning parasite - as its name indicates, it usually goes after beech trees, but sometimes they switch up their target and end up engaging in botanical cannibalism.

Left: The stem and flowers of beechdrops, Epifagus virginiana, Centre: a beechdrops tuber, with adventitious root (ar) indicated, Right: two beechdrops tubers linked via a parasitic connection.
Photos from Fig. 1 and Fig. 2 of the paper.

A botanist named Dr. Luiza Teixeira-Costa was conducting a study on these parasites in the mixed forest at Powdermill Nature Reserve in Pennsylvania, where there is a dense population of beechdrops. After carefully excavating a dozen of those parasitic plants, she noticed one of the specimens was composed of two Epifagus plants locked in a peculiar pairing. When she looked at that specimen more closely, she found that the pair consisted of two beechdrops tubers clinging tightly to each other, as if one of the plant was parasitising its fellow parasite.

To see if there's an actual parasitic connection between the tubers and that this was not two plants that had wrapped around each other via happenstance, Dr. Teixeira-Costa tested whether fluid could be passed between the two plants by injecting one of them with a special tracking solution, and examining it with micro CT scan to create a 3D image of the plants' internal structure. The scanning revealed that there is continuity in the vascular tissue that connects the two plants. It would be like if you find a pair of animals that have joined together and are connected via their circulatory systems. But that was one specimen - perhaps this was just a freakish one-off occurrence?

In order to get a better picture of this phenomenon, Dr. Teixeira-Costa examined the collections of Epifagus specimens at the Meise Botanic Garden and the Harvard University Herbarium, to see if there are more of such pairings. Out of 150 Epifagus that were in those collections, four of them were composed of a pair of E. virginiana plants attached to each other, in a similar way to how these parasites would usually attach to their host. 

In addition she also searched through the online digital archive of herbarium specimen images from 233 herbaria via the SERNEC portal. Out of the 3097 Epifagus specimens in those collections, she found 52 specimens that showed potential signs of parasitising a fellow beechdrops. All those specimens had been collected from across the plant's distribution range in the United States. What this exhaustive search revealed is that while such cases of beechdrops-on-beechdrops is not a frequent occurrence, it is not negligibly rare either. Furthermore, it is widespread and not restricted to just one particular region.

Orobanchaceae plants such as Epifagus are usually able to recognise its own kind and avoid this kind of friendly misfire - so what made some beechdrops turn on one of their own? One possible scenario might involve an Epifagus plant attaching itself to a beech tree root, and was followed by the seed of another Epifagus which responded to the stimuli given off by the tree root. But instead of latching onto the beech tree root, it ended up parasitising one of its fellow Epifagus that was already there.

These examples of intraspecific parasitism have been described as "botanical version of cannibalism" and have been documented in a range of other parasitic plants. If anything, compared with the beechdrops, other parasitic plants seem to be far less discriminating about parasitising their own kind, particularly among mistletoes and dodders. In the world of botanical parasites, sometimes a parasitic plant's worst enemy is a fellow parasite.

Reference:

Teixeira-Costa, L. (2023). Cannibal plants: intraspecific autoparasitism among host-specific holoparasites. Botany 102: 176-183.

Bdallophytum oxylepis

The ecological roles played by parasites can often get overlooked because they are largely hidden from sight, but their presence can have a cascading effect on the rest of the ecosystem. Bdallophytum oxylepis is a parasitic plant that is only found in Mexico, and it parasitises the roots of Bursera trees.

Left and Centre: Trigona fulviventris bees on the flowers of Bdallophytum oxylepis, Right: Arrows indicating the pollen baskets on the legs of T. fulviventris bees. Photos from Figure 4 of the paper

Unlike other flowering plants, this parasite does not photosynthesize - indeed, the plant itself is entirely embedded in the host plant's tissue, with its flowers being the only parts that protrude from the host plant, emerging out of the ground like some kind of exotic mushroom. While the flowers of many other angiosperm plants are brightly coloured, smell sweet and are often filled with nectar, the flowers of Bdallophytum are mostly dark or dull red, do not secrete any nectar, and it smells absolutely dreadful - at least to human noses. This is a common trait among many parasitic plants which often use carrion-feeding insects as pollinators.

Recently, a group of researchers in Mexico conducted a study at a patch of seasonally dry, tropical forest in San Fernando to figure out what animal(s) might be responsible for pollinating this parasite's flowers. Their study took place in 2018 and 2019 during the month of May, in the brief period between the dry and rainy seasons when the parasite's flowers bloom. 

Using a combination of direct observations during the day and camera traps during the night, they watched for any animals that might visit those stinky flowers. They also caught some of the insects that visited the flowers during the day, fixed them in ethanol, and spun them down in a centrifuge to count the number of pollen grains that they ended up carrying after visiting the parasite's flowers. Additionally, they also collected some of the flowers after they have been visited by said insect to count the number of pollen that the visitor had left behind on the stigma

Based on the researchers' observations, insects visited the flowers of B. oxylepis mostly during the day, with midday being peak hour for pollinator traffic. And despite the smell which might have led one to infer that the flower's main visitors would be carrion-loving flies, the researchers discovered that this parasitic flower's main pollinator is in fact a species of stingless bee - Trigona fulviventris, which regularly visited the flowers of B. oxylepis. While the flowers were also visited by ants and the occasional fruit flies, neither of them turned up nearly as often as the stingless bees. Nor do they end up being useful as pollinators since they didn't pick up nor deposit any pollen onto the flower's reproductive parts.

When the stingless bees landed on the parasite's flowers, they helped themselves to more than just its pollen. They treated the flower like an all-you-can-eat buffet, munching on various parts of the flower itself, all while busy shoving pollen into their pockets. But in return for munching on the flowers and hogging all the pollen, each time they visited B. oxylepis, they brought with them a big pollen deposit, plastering the flower's stigma with hundreds of pollen grains. When the researchers examined what type of pollen the bees were carrying, 21 out of 23 bees they looked at only had pollen that came from B. oxylepis. And while T. fulviventris is known to visit a wide range of different flowering plants, it seems the one they like to visit the most in May is this little parasitic flower.

There are a few reasons why this parasite's stinky flowers might be this bee's favourite - T. fulviventris build their hives on the ground near the roots and buttress of trees, and the flowers of B. oxylepis also emerge at ground level. This means that the bees don't have to expend as much energy to reach their flowers. Additionally, B. oxylepis also bloom in May, right at the end of the dry season when the flowers of most other plants are depleted and the newer flowers are yet to sprout. So this parasite is a life-saver for these bees, providing them with the food that they need to survive what would otherwise be a very lean month.

Protecting pollinators means more than just the catchy slogan of "save the bees!" - you need to save the plants they are dependent upon as well, whatever they might be. And sometimes it might just be an obscure parasite that most people would not have even heard of, with flowers that briefly bloom only once a year.

Reference:

Rios‐Carrasco, S., de Jesús‐Celestino, L., Ortega‐González, P. F., Mandujano, M. C., Hernández‐Najarro, F., & Vázquez‐Santana, S. (2022). The pollination of the gynomonoecious Bdallophytum oxylepis (Cytinaceae, Malvales). Plant Species Biology 37: 66-77.

Mitrastemon yamamotoi

Parasitic plant are among the most enigmatic plants on the planet - they spend most of their life completely out of view until it comes time for them to reproduce. Mitrastemon yamamotoi is one such plant, and it is found in the tropical and subtropical forest of Southeast Asia and Japan. This plant parasitises the roots of the evergreen tree Itajii Chinkapin, and only part of this parasite which is visible to any outside observers are small flowers that poke out from the undergrowth - the rest of the plant is completely embedded within its host's roots.

Top: Male stage (left), Transitional stage (centre), Female stage (right)
Bottom: Some of the insect visitors of M. yamamotoi including (from left to right) hornet, cricket, beetle, cockroach
Top row of photos from Fig 1 of the paper. Bottom row of photos from Fig 2 of the paper.

Mitrastemon yamamotoi is protandrous - which means their flowers go through a male phase before transforming into their female form. This kind of sequential sex change is quite common in the flowers of various plants, but it is also found in many different animals as well.

Aside from plants that spread their pollen haphazardly by wind or water, most flowering plants need pollinators - so what would pollinate this parasitic flower? In New Zealand, short-tailed bats are the pollinator for a parasitic plant called the wood rose (Dactylanthus taylorii). In Central and South America, another parasitic plant - Langsdorffia hypogaea - is pollinated by a range of insects (and possibly birds). So what about M. yamamotoi?

A researchers in Japan embarked on a study to investigate the sex lives of these plants, using both direct observation and via remote camera. The remote camera was rigged to be set off by any movement from animals, however insects are too small to be able trigger the camera, so the researcher did it the old fashion naturalist way. This involved spending many hours each day sitting by the flower clusters, watching for any insect that came by, and using red lamps to continue observations during nighttime.

Throughout the period of study between October 2008 to November 2011, the remote cameras failed to capture any photos of animals visiting the M. yamamotoi flowers - since the cameras can only be set off by comparatively larger animals such as birds and small mammals and it seems that none of them were all that interested in the parasite's flowers.

While the flowers of M. yamamotoi seemed have been snobbed by the feathery and furry beasties, they were rather popular with the creepy crawlies. All manner of insect including wasps, crickets, cockroaches, flies, beetles, and ants visited the flowers. Among those, beetles seem to be particular good pollinators as they would visit multiple flowers in one go, carrying with them pollen from each of the flowers that they had visited. The author of the paper did note that since the study was conducted on the southern part of Yakushima Island, this is near northern end of this parasite's distribution, so in other regions it might be visited by different type of animals.

Parasitic plants are among the most endangered organisms on the planet for most of them we don't know just how endangered they might be. Like other parasites, they are deeply interconnected with the rest of the ecosystem. And while insects like wasps and cockroaches tend to get a bad rap from people, for some organisms, they are a vital lifeline.


Reference:
Suetsugu, K. (2019). Social wasps, crickets and cockroaches contribute to pollination of the holoparasitic plant Mitrastemon yamamotoi (Mitrastemonaceae) in southern Japan. Plant Biology 21: 176-182.

Langsdorffia hypogaea

Parasitic plants are important parts of many ecosystems due to the wide range of organisms they interact with. While they can be detrimental to the host plant's growth and reproduction, they are also a food source for many animals. For most parasitic plants very little is known about their basic natural history, let alone the impact they have on the surrounding environment. In the paper featured in this post, a group of researchers conducted a study to collect some much-needed basic natural history information on a common but poorly known parasitic plant call Langsdorffia hypogaea at the Panga Ecological Station, a cerrado reserve located 30 km south of Uberlândia in southeastern Brazil.

The structures of Langsdorffia hypogaea
Top left: Male flowers, Top right: Female flowers, Bottom left: parasitic tuber, Bottom right: the entire plant
From Fig. 1. of the paper

Langsdorffia hypogaea is a widespread parasitic plant found in Central and South America. It has been recorded to parasitise at least 23 different plant species, ranging from lianas, trees, and even a species of cactus. In this study, the researchers found it parasitising five different plant species at the cerrado reserve, with Miconia albicans, also known as Canela de velho, being the most commonly used host plant. It is not easy to spot the parasite's presence - it spends most of its life hidden underground as a parasitic tuber attached to its host's roots, and the parasitised plants do not look visibly different from its non-parasitised cousins.

Unlike hemiparasitic plants such as mistletoes which have leaves and are able to photosynthesis on their own, holoparasitic plants, such L. hypogaea, are wholly dependent upon their host and do not have much in the way of external structures. The only parts of L. hypogaea that poke out of the ground are its red, mushroom-like flowers, which only appear during the dry seasons. So even though it is fairly common, unless you know what to look for, you won't even know that it is there. This is probably why very little is known about it aside from description of its anatomy and the list of plants that it parasitises. Until this and similar studies came along, the most comprehensive research on the natural history of L. hypogaea was published over a century ago.

Since even though it is a parasite, L. hypogaea is still a flowering plant - so what pollinates it?
In New Zealand, an endangered species of parasitic plant called the wood rose (Dactylanthus taylorii) is pollinated by short-tailed bats. In this study, the research team found that the mushroom-shaped flowers of L. hypogaea were visited by a variety of insects ranging from ants, to wasps, to cockroaches. Unlike the wood rose, which produces a prodigious amount of concentrated nectar, L. hypogaea skims on the sugar and secretes a relatively dilute nectar. It is enough to attract many insects, but those insects might not be the plant's main pollinators. Judging from the flower's structure, the research team proposed that the main pollinators of L. hypogaea are more likely to be larger animals like small mammals or birds.

To find out what pollinates L. hypohaea, the researchers set up infrared-based camera traps near its flowers, and the resulting footage revealed a surprising nocturnal visitor - the white-naped jay (Cyanocorax cyanopogon). Aside from insects, those birds were the only animals seen to visit the flowers of this parasitic plant. At this point, it is not known how important the white-naped jays are as pollinators comparing with all the other animals that visit the flowers of L. hypogaea. Indeed, there  is still much which are unknown about this parasitic plant, such as how its seeds are distributed, how it infects the hosts, what effects it might have on their host, and the kind of interactions it might have with the rest of the organisms in the ecosystem.

Organisms which are not well-studied, especially parasites, are not necessarily rare or exotic - they can be fairly common, but because they are hidden out of sight and they are also not on our mind. But to overlook parasitic plants such as L. hypogaeae is to ignore some of nature's most intimate connections and the impact they have on the nature world.

Reference:
Santos, J. C., Nascimento, A. R. T., Marzinek, J., Leiner, N., & Oliveira, P. E. (2017). Distribution, host plants and floral biology of the root holoparasite Langsdorffia hypogaea in the Brazilian savanna. Flora-Morphology, Distribution, Functional Ecology of Plants 226: 65-71.

Cuscata campestris

One of the key characteristic of plants is their ability to produce food using sunlight via the process of photosynthesis. But there are many plants that do not photosynthesise - holoparasitic plants obtain all the nutrient they need from their host. One of the most well-known group of holoparasites are the dodders. There plants have no roots, their leaves have been reduced to tiny scales, and are composed entirely of elongated tendril-like vines. Because of their appearance and what they do to the host, the dodder has also acquired many common names including "Angel Hair", "Witch's Hair" and "Devil's Hair". When the dodder latches on to an appropriate host, it extends structure call haustoria which penetrate into the host plant's tissue to suck out its nutrients. This has led to the dodder also being called "vampire plants".

Dodder seedling in the process of coiling around its host (image from Fig. 1. of this paper)

There are 200 known Cuscuta species and of those, a small handful of them (10-15 species) are considered as serious agricultural weeds. These parasitic plants wrap their vines around their hosts and literally suck the life out of them. Infestation of this plant have been known to cause massive losses in alfalfa, tomatoes, carrots, and cranberry crops, and these "vampire plants" are very difficult to get rid off; since dodder vines often completely smother their hosts, it requires a lot of manual and mechanical labour to remove them. Additionally, dodders can also produce large numbers of resilient seeds that can linger in the soil for a long time, waiting for the next year to erupt in another outbreak.

For dodders, as with most other organism, the first moments of its life are the most critical - the newly germinated dodder seedling must secure a grip on a host plant within two to three weeks of germinating, otherwise the seedling would use up its energy reserves and expire. From the moment they germinate, these parasitic plants have various ways of finding their host. Dodder vines are able to "sniff out" host plants through the chemical they give off (essentially plant BO), but they can also use other senses to find their host. A newly germinated dodder seedling can also detect the specific wavelength of light which are reflected off the surface of plants, and use it to reach a host.

The scientists in this study investigated whether exposing dodder seedling to different spectrum of light can disrupt their ability to find their hosts. They conducted their experiments on the seedlings of two dodder species - Cuscuta campestris (which parasitises tomatoes) and Cuscata gronovii (which parasitises jewelweeds), and exposed them to three light source with different spectrums - the spectrum similar to unfiltered sunlight, mostly red light, and mostly far red light. Far red is a wavelength of light which is barely visible to our eyes, but it is the wavelength which is most reflected by the surface of plants. It is also the wavelength which dodders use to home in on their host.

From the experiment, the scientists found that almost all the dodder seedlings that were exposed to unfiltered light and mostly far red light were able to attach to a host after a week or two, in fact those bathed in far red light grew faster than the other groups. However, most of those that were bathed in red light lost their ways. Only 15% of the C. campestris and 27.2% of the C. gronovii seedling that were exposed to high levels of red light had managed to wrap themselves around a host.

So will it possible to control dodder infestation simply by bathing crops in red light? No, not quite since some dodder still managed to wrap themselves around a host plant and the red light treatment is only effective during the earliest stage of the dodder's life. But at least the findings of this experiments have shown that perhaps light manipulation can be combined with other control methods to control dodder infestation.  Additionally, we have gained an insight about how these parasitic plants sense and find their way through the world.

For this particular vampire, its weakness is not against sunlight, but rather, red light.

Reference:
Johnson, B. I., De Moraes, C. M., & Mescher, M. C. (2016). Manipulation of light spectral quality disrupts host location and attachment by parasitic plants in the genus Cuscuta. Journal of Applied Ecology 53: 794-803.

P.S. I recently drew some dodder-inspired art, yes, it is more Parasite Monster Girls - meet Cassandra the Dodder...

Macrodasyceras hirsutum

On this blog, we have featured many parasites that drastically alter the appearance and/or behaviour of their host, usually to make them more likely to be eaten by the next host in the parasite's life-cycle. But today, we are featuring a parasite that makes their hosts appear less appetising - a seed parasitoid that has other plans for its host - none of which involves being eaten.

From the perspective of the plants that produce them, fruits are a way to turn animals into willing seed couriers. By wrapping seeds up in a tasty package, plants can deposit their seeds temporarily inside the body of an animal that will carry them off to a new location. We have even featured a (parasitic of course) plant on this blog that uses beetles for such a purpose.

photo from Figure 1 of the paper

Unlike the rest of the plant, which is often indigestible and laden with defensive toxins, the fruit is supposed to be attractive and appetising to would-be animal dispersers. However seed parasitoids such as Macrodasyceras hirsute have other plans for the fruits - they do not care for the fruit's flesh - they are only after the nutritious seed. Unlike the parasite we featured in the last post, the gullet of a bird is a death sentence for the larvae of this parasitoid (though as always in nature, there are some exceptions), which is a bit of an inconvenience as the fruits it parasitises are meant to be eaten by birds.

Macrodasyceras hirsutum parasitises the fruit of the mochi tree Ilex integra and all it wants to do is to live out its larval stage munching on seeds and grow up to be a wasp. It would rather not have its life suddenly interrupted by a hungry bird feasting on the mochi tree's bright red ripe berries.

So to ensure that its home will not end up tumbling down the throat of a bird, M. hirsutum larvae counteract the berry's usual ripening process, and ensure that it stays green (and unappetising to birds, which disdain unripe berries). A team of Japanese scientists found that if they shielded the fruits from wasp attack, almost all the mochi berries ripened to red. But, if they are exposed to M. hirsutum, some of them stayed green, and all the berries that stayed green had M. hirsutum larvae living inside them. Furthermore, they found that the more larvae there are in the berry, the more intensely green the fruit becomes - M. hirsutum did not merely stop the berries turning from green to red, they actually turned the dial on the green tone all the way up.

This little wasp is not the only insect to do this. Holly berries infected with a species of midge also stay green. It is unknown how this wasp interferes with the berry's pigment production/development, though for the holly berry midge it has been suggested that a symbiotic fungi is responsible for maintaining the host fruit's green colour. The relationship between fruit-bearing plants and fruit-eating animals has evolved to be a mutually beneficial interaction whereby one party provides food (fruits) while the other returns with a service (seed dispersal). But, the actions of M. hirsutum and other such seed parasitoids tinkering away in the background can certainly undermine the effectiveness of this mutualistic partnership if they cause otherwise ripened fruits to go uneaten. The extent of the impact such seed parasitoids have on the ecology and evolution of such plant-animal interaction is currently unknown.

Reference:
Takagi, E., Iguchi, K., Suzuki, M. and Togashi, K. (2012) A seed parasitoid wasp prevents berries from changing their colour, reducing their attractiveness to frugivorous birds. Ecological Entomology 37: 99-107.

Cuscuta chinensis

Today's post has some plant-on-plant action, featuring a species of dodder. Dodders are a group of holoparasitic plants made up of about 100-170 species. They are plants that consistent entirely of stem, with leaves that have been reduced to tiny scales. They smother the host plant in a tangled mess, and dig deep into the host tissue using modified roots called haustoria to draw out water and nutrients. We have previously featured the European Dodder on this blog, but today, we will be looking at the Chinese Dodder Cuscuta chinensis, and how it interacts with plants that are not native to its home range.

Image Credit: Jayesh Patil

There are many studies that look at characteristics of successful invasive species (an introduced species that has subsequently become a pest). Generally, plants that have become invasive after their introduction have faster growth rates and are able to utilise nutrients more efficiently, allowing them to outcompete the native flora. In addition, according to the "enemy release" hypothesis, one of the reasons why newly introduced plants and animals become so successful in their new homes is because they are freed from the burden of their natural predators and pestilence, thus allowing them to propagate unchecked across the new land. While this seems to indicate that the best way to control invasive species is to introduce their natural enemies as well, the main problem is that you are introducing yet another new species. Remember that folklore about the old lady who swallowed a fly and subsequently introduced a sequential menagerie into her body? You don't really know what cascading effects the new biological control species will have on the local ecosystem - after all, the cane toad (Bufo/Rhinella marinus) was introduced to Australia to control beetles in sugar cane plantations, but have since become a huge ecological problem.

The higher growth rate and resource-usage efficiency of these invasive plant does have a drawback though - it makes them more attractive targets to parasites. So what if a native parasite can turn the table on the invaders? What if a native parasite acquires a taste for an exotic new host?

The Chinese Dodder is a parasite with eclectic tastes, as it is capable of infecting more than 100 species of wild and cultivated plant species. To find out how well C. chinensis grows on native flora compared to their introduced counterparts, a team of researchers in China evaluated the performance of C. chinesis on 3 invasive plant species and the native equivalent from the same genus. They found that not only did C. chinensis grow much more prolifically on the introduced plants,but it also caused more damage. In fact, C chinensis is more damaging to plants that are more efficient in using their resources - the very trait which makes them so good at being invasive in the first place.

There is also another possibility - one which the researchers did not mention in the paper: Unlike the native plants which have had a long co-evolution history with the dodder and have thus evolved various means to counter the parasite's tricks blow-by-blow, the naive introduced species have never encountered C. chinesis before, which leaves them more vulnerable to attacks by the parasitic dodder. For those exotic introduced plants, it seems that the very thing which had brought them so much success in their new home may end up causing their downfall when confronted with a certain holoparasite.

Reference:
Li J, Jin Z, Song W (2012) Do Native Parasitic Plants Cause More Damage to Exotic Invasive Hosts Than Native Non-Invasive Hosts? An Implication for Biocontrol. PLoS ONE 7(4): e34577. doi:10.1371/journal.pone.0034577

Rhinanthus minor

Many parasites can have substantial effects on their hosts, but their impact can often extend to other organisms in the environment. Today's parasite is one of the more pretty-looking ones which we have featured in a while - as opposed to the usual worms and lice, today we are featuring a flowering plant - the yellow rattle. But don't let its pretty yellow flowers fool you, Rhinanthus minor is a ruthless parasite.

It is a hemiparasite (like the mistletoe , which becomes rather popular during this time of the year). The plant overwinters as seed in the soil and germinates during spring, penetrating into the roots of its host plants where it can suck out nutrients and water from the plant's xylem tissue. The yellow rattle is a fast growing plant - it flowers 12 weeks after germination and 3 weeks after that it produces seeds that are loosely held in dry capsules, which gives the plant its name. The yellow rattle often share its host plants with a range of insects, so a group of researchers in the UK decided to look at how this hemiparasite can affect those insects. Specifically, they looked at the effects of R. minor on insects that exploit plants in different ways; the aphid that feeds on the sugary sap flowing in the plant's phloem, the spittle bug, which taps into the xylem that transports water and other nutrients, and the grasshopper, which simply chews on leaves.

The researchers predicted that over the course of its growth, the yellow rattle would affect those insects differently. They were expecting that it would negatively impact on the spittle bug, because that insect and the hemiparasite both draw their nutrients from the host's xylem. But as is often the case in science, they found something unexpected.

First of all, they found that the effect R. minor had on those insects depended upon the parasite's growth stage, and it becomes most pronounced when the yellow rattle reaches its peak biomass and begins setting seeds. However in contrast to what they were expecting, spittle bugs actually preferred plants parasitised by R. minor. But the insect that benefited the most from the hemiparasite's presence were the aphids. Not only did they prefer sharing a host plant with the yellow rattle (there were three times as many aphids on plants with R. minor compared to uninfected plants), they also tend to breed more on infected plants. What about the grasshoppers? Grasshoppers were not all that affected by the presence of the yellow rattle either way.

The mechanism behind why the yellow rattle makes its host more attractive to plant-feeding insects is currently unknown. However, it may have something to do with the hemiparasite altering the water content of the host plant, or changing the composition of the phloem sap, which makes it more nutritious to aphids. Either way, it seems that at least for some insects, sharing a plant with a hemiparasite might actually be a good thing.

Image from the Wikipedia.

Reference:

Ewald, N.C., John, E.A. and Hartley, S. (2011) Responses of insect herbivores to sharing a host plant with a hemiparasite: impacts on preference and performance differe with feeding guild. Ecological Entomology 36: 596-604.

Bursaphelenchus xylophilus

Today's parasite is the nematode Bursaphelenchus xylophilus, a well-known tree-killer responsible for the devastating plant disease known as pine wilt. Originating in North America, it has since been spread over much of Asia, and has recently been introduced to Europe. This nematode is transported by longhorn beetles known as "pine sawyers", and gain initial access to the tree through the feeding wound created by that insect. So the arrival of a B. xylophilus-laden beetle pretty much amounts to a death sentence for a pine tree. While pine trees in North America have coevolved with B. xylophilus and developed resistance or tolerance for the parasite, it has caused widespread wilting and death to the pine trees of Japan. So how can such a tiny worm bring down an entire pine forest?

For B. xylophilus, or any other plant parasites for that matter, a tree is a formidable fortress - protected by walls and scaffolding of tough cellulose, and canals of deadly resin. Plant cell wall presents the main barrier to any plant parasites - it is a tough material to break down, and most animals are incapable of doing so without the aid of symbiotic microbes. In addition, the vascular tissue of many coniferous plants like pine are saturated with resin - a thick, sticky cocktail of aromatic chemicals (from which we derive many useful substances including solvents, varnishes, adhesive and perfume) which would overwhelm and kill most invaders. Yet none of those defenses seem to deter B. xylophilus - not only can it break through the thick cellulose barrier of the pine tree, it actually lives within the resin canals of its host, which is practically the most lethal place within the tree. It would be akin to living in a moat of toxic tar.

A recent study published in PLoS Pathogens on the genome of B. xylophilus offers vital clues to how this nematode exploits its pine tree host. One of the most important enzymes for plant exploitation is cellulase - it is used to break down cellulose structures and allow potential parasites to enter and navigate through the host. Bursaphelenchus xylophilus is able to produce a unique combination of 34 enzymes for breaking down cellulose and carries a diverse suite of genes for producing enzymes that detoxify the aromatic compounds found in resin. So how did this tree killer acquire the necessary molecular machinery to invade and disarm its host?

The wide range of detoxifying genes in the B. xylophilus genome appear to be multiple duplication of pre-existing genes which are also found in other nematodes, such as the well-known standard lab worm Caenorhabditis elegans - B. xylophilus just happen to have more of copies of those genes to cope with the wider array of toxins it encounters. However, the cellulase genes have a much more unusual origin. Out of the 34 cellulase enzymes produced by B. xylophilus, 11 of those enzymes are not found in any other nematode, but are most similar to those produced by fungi. So how does a nematode end up producing fungal enzymes?

The answer might be through horizontal gene transfer (HGT). The closest living relatives of B. xylophilus are fungi-eating worms which are transported by beetles to dead and dying trees. Once they reach their destination, they disembark from their beetle vectors and feed on the fungi which have colonised the dead trees. In a case of you are what you eat, the ancestors of B. xylophilus appeared to have incorporated a whole suite of useful genes from their food, allowing them to bypass the process of feeding on fungi which are growing on dead trees and just go straight to breaking down live plant tissue.

Image from figure of the paper.

Reference:

Kikuchi T, Cotton JA, Dalzell JJ, Hasegawa K, Kanzaki N, et al. (2011) Genomic Insights into the Origin of Parasitism in the Emerging Plant Pathogen Bursaphelenchus xylophilus. PLoS Pathog 7(9): e1002219. doi:10.1371/journal.ppat.1002219

Cytinus hypocistis

For a change of pace today the blog is going to feature a parasitic plant. Cytinus hypocistis is a holoparasitic plant, which means that unlike ordinary plants it does not perform photosynthesis, but obtains all the nutrients that it needs from its host. Cytinus hypocistis is embedded entirely within the the root of its host plant, but in spring, it pokes flowers out of the ground, which are then pollinated by ants and ripen into berry-like fruits. Each of these fruits contains thousands of tiny seeds, each about 0.2 mm in length.

What makes C. hypocistis unusual is that while most fruit-bearing plants rely upon vertebrate animals to disperse their seeds, C. hypocistis mainly uses a beetle. Researchers found that the seeds collected from beetle frass (fancy name for insect poop) are just as viable as seeds which are collected directly from the fruit. While rodents and rabbits also frequently consume C. hypocistis fruits, because they have a tendency to eat immature fruits and deposit their dung (with any viable seeds) at ground level, they are not as effective as the beetles. Not only do the beetles consume only fully-ripened fruits, they also have a tendency to bury themselves into the sand during midday, which can bring the seeds closer to the roots of the host plant.

This is one of the few known case of endozoochory (where the seed is consumed and pass through the gut of an animal) which involves an insect. The researchers of this study pointed out that this type of ecological interaction may in fact be quite widespread and common, especially for plants with very small seeds. However, they have simply been overlooked because all those involved were, quite literally, lurking meekly underneath our feet.

Reference:
de Vega C, Arista M, Ortiz PL, Herrera CM, Talavera S (2011) Endozoochory by beetles: a novel seed dispersal mechanism. Annals of Botany 107: 629-637.

December 29 - Eremitilla mexicana

Back in 1985, Wayt Thomas, a scientist from the New York Botanical Garden discovered an unusual plant in Mexico. It had a little bloom of dense flowers that kind of looked like a pinecone and nothing else but a thick stalk - no leaves or chlorophyll anywhere. It was so unusual that Thomas did not know what it was and could only speculate as to even what family it might be in. The strange plant eventually made its way to George Yatskievych at the Missouri Botanical Garden and twenty years after it was first discovered, he traveled back to Mexico in search of more. He went to the same location - and even employed the very same guide that Thomas had - and finally, after several days of hunting through stream beds in the Sierra Madre del Sur, they found a small population and took a few samples and many photographs. They did not collect very many because it is believed to only occur in this one small region - it has never been observed elsewhere. A second trip allowed Yatskievych to identify the host plants as Hedyosmum mexicanum and it has now been named Eremitilla mexicana, which means "little Mexican hermit."

Photo by George Yatskievych.

December 27 - Macrophomina phaseolina

One of the gifts that the Three Wise Men brought was frankincense, which is derived from the resin of the tree Boswellia serrata. While frankincense has been considered as a remedy for many different types of infectious diseases, B. serrata itself is by no means free from the scourge of infection itself and is plagued by the fungus Macrophomina phaseolina, which causes the disease known as Charcoal Root Rot. This fungus infects more than 300 species of plants, and can cause high mortality among tree seedlings. Macrophomina phaseolina survives and overwinters as small, black spores (call microsclerotia), hidden in the soil or debris from previously infected plants. When a growing root of a plant encounters a dormant spore, it germinates and begins growing all over the root and penetrating into the root cortex. From there, the fungus penetrates through the cortex and inner bark and into the taproot. The infected seedling eventually dies from the gradual destruction of its root system. Just prior to the death of the host, the M. phaseolina produces spores that are deposited in the inner bark of the lower stem and roots. When the host eventually dies and decays, the spores are released into the soil where they wait for an encounter with yet another growing seedling.

Contributed by Tommy Leung.

December 21 - Nuytsia floribunda

During Christmas time in Western Australia, Nuytsia floribunda begins to flower, displaying bright orange flowers and earning itself the name "Australian Christmas Tree". Despite its name, it does not resemble the typical image of a Christmas Trees from the Northern Hemisphere. In fact, N. floribunda actually more closely resembles another Christmas-themed plant - the mistletoe - for N. floribunda is also a hemiparasite. Like other parasitic plants, they have a modified root structure call a haustorium which penetrates the roots of their host plant. The haustorium of the Australian Christmas Tree is armed with sickle-like "horns" with which it to cut its way into the root segments, allowing the Christmas Tree to tap into the flow of water and other chemicals. Interestingly, unlike most other parasites, an individual Australian Christmas Tree can actually exploit multiple hosts at the same time, spreading out a network which is linked to the roots of multiple host trees. And they are certainly not discriminating about whom they network with - most species of trees are vulnerable to invasion by their haustroia, and even underground cables have been found to have the haustoria of N. floribunda attached to them!

Contributed by Tommy Leung.

December 17 - Viscum album

A cozy fire burning in the hearth, carols tinkling in the background, a glass of spiked eggnog in your bellies...what could be more romantic than finding yourself underneath a sprig of mistletoe hung in the archway with a sweetie, right? That is, if you don't mind kissing under a parasite. Viscum album, the European mistletoe is a parasite of more than 200 different trees and shrubs. It is hemiparasitic in that it still possesses chlorophyll but relies on its host plant for both water and other nutrients. Birds eat the juicy berries and then the seeds pass out in their feces and stick to the branch that they happen to land on, where they will germinate and set up a new parasitic plant. Mistletoe can severely damage or even kill their hosts if the infection is intense enough. The connection to Christmas is fairly recent, thought to have begun in the 18th century, and has evolved from a symbol that protected the home from fire to the more amorous excuse to kiss a pretty girl who happens to walk under it. This species, with its white berries, is more popular in Europe (and in plastic varieties everywhere); other mistletoe species (all also parasites) are used in other parts of the world.

November 20 - Pedicularis groenlandica

Pedicularis groenlandica, or as it is commonly known as because of the shape of its flowers (see insert), Elephant's Head or Elephanthead Lousewort (a big handle for a little flower!) is a parasitic plant in the broomrape family (see also Boschniakia hookeri and Orobranche californica). These plants can be found in - you guessed it - Greenland, but also across Canada and into western North America. P. groenlandica uses haustoria to penetrate the roots of other plants and then suck their water and nutrients out.

October 24 - Lathraea clandestina

Today we have a pretty parasite - Lathraea clandestina, or the Purple Toothwort, is a parasitic plant that uses willows, poplars and alders as its hosts. Its name comes from the fact that its remnant, below-ground and chlorophyll-less leaves resemble teeth. These plants produce quite large fruits for their size, which burst when ripe, sending their tiny seeds off to be carried by rain or other moisture to new hosts. L. clandestina is found throughout Western and Central Europe and seemingly were recently introduced into the U.K. and Ireland.

September 1 - Dactylanthus taylorii

Dactylanthus taylorii is a holoparasitic plant, meaning that it does not possess any chlorophyll of its own and derives all of its nutrients from its host plant, which is commonly the Seven-finger (Schefflera digitata). When infected, the host tree will produce a malformation, or burl, that resembles a wooden rose, hence its common name, the Wood Rose. The flowers are pollinated by the Lesser Short-tailed Bat (Mystacina tuberculata), which are drawn to its odor and abundant nectar. This species, native to New Zealand, is sadly critically endangered there and is the subject of aggressive conservation plans.