Parasitic Plants: Nature’s Uninvited Guests

Types of parasitic plants

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You may be familiar with parasites in the animal kingdom, but did you know that there are also parasitic plants? These plants attach to their hosts to take nutrients and water. Without their hosts, they simply couldn’t survive.

While there are downsides to parasitic plants, they can also be of benefit. In this guide, we’ll look at the effects of parasitic plants and get to know a few species a little better.

What are Parasitic Plants?

What are parasitic plants?
Corpse Flower (Rafflesia arnoldii) is a Holoparasite that Parasitizes Several Species of Plants Including the Tetrastigma

Parasitic plants actually make up around 1% of all flowering plants, scientifically known as angiosperms. There are around 4100 species in total. These are plants that either completely or partially rely on their host for their nutritional needs.

These plants are different to others in that they have a specialized organ known as the haustorium, a type of root that they use to attach to their host. Through this, they are able to absorb water and nutrients and in some cases can even take the products produced via photosynthesis.

The plants will connect to their hosts via xylem feeding or by the phloem; both of these are types of vascular tissue found in plants. In some cases, parasites will connect to both.

But it hasn’t always been this way. You might wonder why there are even parasitic plants in the first place. It’s all down to evolution and the development in some angiosperms of the haustorium. Amazingly, though, during this evolution, parasitic plants developed a self-incompatibility so that they do not end up parasitizing themselves.

Types of Parasitic Plant

Some parasitic plants rely heavily on their host plants, whereas others are only partially parasitic.

Partial Parasitic Plant (Hemiparasites)

A partially parasitic plant, sometimes known as a hemiparasite actually has the ability to photosynthesize. They may have chlorophyll so they are able to produce their own nutrients but these plants will thrive better with a host, especially when they’re growing in areas where the nutrient level is poor.

While they are able to survive without a host, partially parasitic plants will benefit from having one. This is often referred to as a facultative parasite which essentially means an organism that will resort to parasitism when needed in order to survive.

In order to take some of their required nutrients, these plants will attack the xylem (vascular tissue) of the host below the ground.

Interestingly, because they parasitize below the surface, these plants may look, for all intents and purposes, just like any other type of plant.

Total Parasitic Plant (Holoparasites)

Unlike partially parasitic plants, total parasitic plants rely solely on their hosts for all of their nutritional needs. They are known as holoparasites and do not have their own chlorophyll; in short, without a host, they would not survive.

Obligate parasites like these have very complex lifecycles and will often move between hosts attacking both the xylem and phloem of the host plant. The problem is that, while these plants cannot survive without their host, they may end up causing some damage to it.

In the United States, many total parasitic plants are seen as invasive species and have even been known to kill their hosts, completely draining them of their resources.

Benefits of Parasitic Plants

Benefits of parasitic plants
Dodder Vine (Cuscuta spp.) – a Parasitic Vine, has been Used in Traditional Medicine as a Treatment for a Variety of Ailments

Understanding the potential damage that a parasitic plant could cause may lead you to believe that they’re totally harmful. However, there are some benefits that they bring.

Enhance Nutrient Cycling

While parasitic plants may be taking nutrients from other species, they’re also cycling nutrients which in turn benefit things like herbivores and pollinators. Just like anything else, they have their place and uses within an ecosystem.

Supress Invasive Species & Improve Plant Diversity

It’s been shown that having parasitic plants can help to suppress certain grasses and unwanted plants, allowing other species to grow and therefore increasing biodiversity. This has been proven in science, and in areas where certain parasitic plants were taken away, there was a significant loss of several species.

This is nothing but positive and further studies have shown that while there tends to be a lower mass of plants, there is far richer diversity where parasitic species are found.

Used for Medicinal Use

Humans have long turned to nature for medical purposes and it seems that parasitic plants play an important role within this.

Scientists are currently looking at around 100 species of parasitic plants for their potential medicinal uses. Plus there are even some species that produce edible fruits that have their own series of health benefits.

Drawbacks of Parasitic Plants

Drawbacks of parasitic plants
Root Parasitic Plants such as Broomrapes (Orobanche & Phelipanche spp.) can have a Negative Impact on Crop Yields

There may be some good things associated with parasitic plants. But by their very nature, they can also be pretty damaging.

Can Take Over Existing Plants

Some parasitic plants are seen as invasive, and it’s no wonder when you consider how easily some of them can take over an area. They will deprive their hosts of water and nutrients, which stops them from thriving, allowing the parasite to take over. Naturally, this will throw out the balance of local ecosystems, causing significant damage.

Cause Economic Damage Due to Crop Loss

The threat to human crops comes in many forms and one of these is the parasitic plant. In Africa, for example, the witchweed is known for its ability to attack crops like maize, millet, and rice. This is known as one of the most harmful plants as is the boomrake which poses a threat to the ability of farmers to grow legumes in the Middle East.

Of course, once these plants begin taking over crops, this poses a real risk of loss to farmers which has a serious impact on the economy.

Transmit Pathogens

Since parasitic plants attack their hosts through the roots in at least 60% of cases, it is very easy for harmful pathogens to be transferred between species. This is one of the main ways in which parasites damage or even kill their hosts.

Studies of the two most common families of parasitic plants have shown that they are the main mode of transmission for phytoplasmas.

Types of Partial Parasitic (Hemiparasites) Plants

With over 4000 species of parasitic plants, you’ll find that they fall into one of two categories. Partial parasitic plants don’t fully rely on a host, but they’ll do much better if they have one.

1. Mistletoe (Genus: Viscum, Phoradendron, Arceuthobium)

Most of us associate mistletoe with Christmas, but what you may not know is that it is a hemiparasite. Mistletoe typically grows on the branches of a host tree, using haustoria to penetrate the host’s bark to draw water and nutrients to help sustain itself. It parasitizes a variety of trees, including hawthorns, oaks, elms, limes, poplars, and conifers.

There are over 1000 species of mistletoe. While not all species are parasitic, the European mistletoe (Viscum album), the American mistletoe (Phoradendron serotinum), and the dwarf mistletoe (Arceuthobium spp.) are parasitic species.

Generally, mistletoe will be spread by birds feeding on the plant’s berries, thus helping to disperse its seeds. The lodgepole pine dwarf mistletoe (Arceuthobium americanum), however has a unique way of spreading from tree to tree. As the berries ripen, they will break open, forcibly ejecting the seeds at high velocity and releasing a sticky white substance called viscin, which then gets deposited onto the branches of a new host tree.

2. Loranthus (Loranthus spp.)

Loranthus is a plant that’s part of the mistletoe family and will attach to the branches of more mature woody trees and plants.

It’s found growing commonly in India as well as parts of Africa and is known to be one of the most significant pests of the cocoa tree. However, they also attach to citrus crops and will reduce their growth, therefore making them a problem for farmers.

3. Indian Paintbrush (Castilleja spp.)

The Indian paintbrush is one of 200 species within this family of plants and is actually part of the broomrape family. It has distinct bright red flowers that really stand out in the grassland and semidesert habitats of the plant.

Hummingbirds are hugely attracted to the Indian paintbrush for its nectar but owing to the lack of any perch, other birds show little interest in it.

Indian paintbrushes are found growing in parts of Northern Asia but are also very common along the western parts of America all the way from Alaska down to the Andes. Their main hosts are various types of grasses.

4. Indian Sandalwood (Santalum album)

It may surprise you to learn that sandalwood, a type of woody plant, is actually parasitic. After all, it’s so commonly used by humans for things like medicine, aromatherapy, and in perfumes and cosmetic products. It’s so highly prized that it can cost up to $3000 for just 1 kilo!

Sandalwood could be one of 25 species that are found in Northern Australia, the Pacific Islands, and most notably, in India. However, Indian forests have largely been cleared and now it’s rare to find sandalwood in the wild.

Farmers taking care of plantations have to make sure that they also plant hosts for the sandalwood, particularly those within the acacia genus.

5. Western Australian Christmas Tree (Nuytsia Floribunda)

It might sound festive, but the Australian Christmas tree is a relentless plant whose haustorium acts like a guillotine, chopping the xylem of the host and sapping the nutrients. It’s such an effective weapon that it’s even been known to cut through fiber optic cables!

While only partially parasitic, these trees benefit from a host, especially during the dry season as the additional nutrients and water help it to flower.

6. Velvetbells (Bartsia alpina)

Velvetbells are found growing in the mountainous regions of Europe and are sometimes called alpine bartsia. They are also common in places like North East Canada, Iceland, and Greenland where they prefer rocky and barren areas with a lot of natural light. They were once common in the United Kingdom, but numbers have seriously declined due to damage from livestock. They’re now only found in very northern parts of the country.

The velvetbell has a hairy, purple stem and attaches to Alpine grasses in order to take nutrients and water.

7. Yellow-Rattle (Rhinanthus minor)

Not to be confused with the white yellow rattle, which is not a parasitic plant, the yellow rattle is one of the more beneficial species of parasites. It is known for its ability to improve biodiversity in its natural meadow habitat, where it will attach to host grasses and legumes.

This very fast-growing plant will weaken these plants, making way for other species. They are mid-sized and can grow to around 20 inches (50 cm) in height.

8. Eyebrights (Euphrasia spp.)

Eyebrights come in many shapes, sizes, and colors. While they were once classed as an individual species, they’ve now been broken down into subspecies to make each one more easily identifiable.

These partial parasitic plants are often found growing in woodlands and meadows, where they will attack grasses and can cause some serious damage owing to how much they weaken their hosts.

While there are more than 450 sub species of eyebrights, most are only found in Europe, although they are very widespread here. They’re only small plants that don’t typically get any larger than 6 inches (15 cm) in height.

9. Red Witchweed (Striga asiatica)

Out of all of the partially parasitic plants, the red witchweed, as well as other species of witchweed, are among the most devastating to their hosts. These plants are found in Africa and Asia but have been introduced to other parts of the world, including North America and Australia.

In the USA, they were initially found in the Carolinas, where they quickly became a pest due to the damage they do to crops. However, there has been a significant success where eradication programs are concerned, and numbers have dwindled by up to 99%.

In their native locations, red witchweed plants will parasitize crops like maize, sugarcane, and rice, causing yields to decrease by up to 70%!

Types of Total Parasitic (Holoparasites) Plants

Some plants are unable to photosynthesize and rely solely on their hosts to keep them alive.

1. Balanophora (Balanophora spp.)

Balanophora has a unique ability to emit a strong odor to attract pollinators. While it reproduces this way, it also needs water and nutrients to survive which it takes from host plants like the rubber tree, cocoa tree, and the oil palm.

It attaches to its hosts using tuberous rhizomes under the ground that connect to the tree’s roots.

These plants are common in both the tropical and temperate regions of Asia as well as tropical African regions and parts of the Pacific Island group. There are 20 species in total, and they are often used for medicinal purposes in Asia as well as their waxy substance being used as torch fuel and for candles.

2. Dodder Vine (Cuscuta spp.)

The dodder vine, sometimes called Cuscuta or the wizard’s net, has no leaves or roots and instead has the appearance of a stringy mass of stems. They’re a part of the morning glory family and without a host, would only survive between five and ten days.

Their stems will grow in the direction of their host when they sense it. But what’s fascinating is that the plant uses chemical signals from the new host so it knows when it’s time to flower. When it’s time, the dodder vine will penetrate the host stems with its haustoria, and most species are totally at the vine’s mercy and unable to resist. But there are some, such as the cultivated tomato that has developed something of a defense system against dodder vine. 

Plants that are unable to defend themselves will often die as this is an incredibly aggressive species that will sap nutrients, making it impossible for the host to survive.

3. Corpse Flower (Rafflesia arnoldii)

The corpse flower can lay claim to being the biggest individual bloom in the world. While there are plants that may appear to have larger flowers, these tend to be made up from a series of smaller ones.

This plant also boasts a rather pungent aroma that’s often compared to the smell of rotting flesh. While it’s unpleasant to humans, it actually attracts things like flies and rodents that will pollinate the plant.

Corpse flowers parasitize tetrastigma vines and have thread-like strands that attach to the roots of their hosts. You wouldn’t even know they were there most of the time as they’re only visible when they produce their 3-foot (1 meter) flowers!

4. Toothwort (Lathraea spp.)

Toothwort is a type of parasitic plant that can be found growing in temperate regions of Europe and Asia. There are only between five and seven species of this plant which has a system of branch-like structures under the ground and attaches to the roots of its host.

These are carnivorous plants that have cups with hairy stalks on the inside. When they are triggered by insects, the plant sends out filaments to feed on them.

Above the ground, all you see are the small purple flowers, but below the surface, toothworts are taking nutrients from willows and poplars in damp wooded areas.

5. Squawroot (Conopholis americana)

The squawroot is native to North America, although it can be found in other places throughout the world so is not considered to be endemic.

These interesting-looking plants have a similar appearance to a pinecone sitting on the ground, but underneath the soil, they attach to the roots of oak and beech trees.

Squawroot prefers a wooded location and is usually found growing in and around ravines. That said, it’s a pretty uncommon plant and relies on mammals like deer and bears to spread its seeds.

6. Beechdrops (Epifagus virginiana)

Charles from Mille-Isles, Canada / Wikimedia Commons / CC BY 2.0

Beechdrops is very specific about which plant it parasitizes, hence its name. It will only attack the American beech and tends to attach to the shallower roots of the tree.

Beechdrops does not have a haustorium but instead uses a tuber to connect to its host. There have been cases where it has been seen attached to the maple, but this is thought to have happened by mistake.

It’s most common in the northeastern parts of North America and has a straight brown stem with white and purple flowers.

7. Thurber’s Stemsucker (Pilostyles thurberi)

Matt Berger (image rotated) / Wikimedia Commons / CC BY 4.0

Thurber’s stemsucker is native to the southwestern parts of North America where it can be found growing in desert environments. Its main hosts are shrubs within the pea family and the stemsucker will live inside the plant until it is time to flower.

However, even when it flowers and the blooms can be seen on the outside, they’re only tiny, and the whole plant might only get to around 0.2 inches (6 mm).

Interestingly, scientists are yet to have discovered what animal or method this plant uses for pollination.

8. Dutchman’s Pipe (Monotropa Hypopitys)

Sometimes called the pinesap or yellow bird’s nest, the Dutchman’s pipe grows all over the northern hemisphere. It prefers temperature regions and can be found growing in forests, particularly where conifers and pines are in abundance.

The Dutchman’s pipe doesn’t actually connect to the tree but to a fungus that already has a symbiotic relationship with the host tree.

These plants can grow up to 10 inches (25 cm) in height and have a sweet fragrance that isn’t all that dissimilar to vanilla.

9. Albino Redwood (Sequoia sempervirens)

The albino redwood can be found growing exclusively in California within certain state parks. This is one of the rarest types of parasitic plants, and is therefore heavily protected. So much so that the actual location of the individual trees is undisclosed.

Instead of the green needles we’re used to seeing on redwoods, these have white needles owing to the lack of chlorophyll.

The albino redwood is seen emerging from the base of the host tree, where it attaches to the roots and takes sugars. But they’re also beneficial to their hosts as the albino redwood will store toxic matter, keeping it away from the parent tree.

10. Bird’s-Nest Orchid (Neottia nidus-avis)

The bird’s nest orchid is common across the Middle East, Russia, and Europe and is a mid-sized plant that grows up to 15 inches (38 cm) in height.

These are heavily flowering plants with up to 60 blooms on each shoot and like a shady spot, preferably in a wooded area.

Their most common host is the beech tree, but the plant will actually connect to a fungus that’s already connected to the tree. From this, the plant is able to take the nutrients that the fungus has absorbed from the soil.

Interestingly, these plants emit a sweet, musty odor to attract pollinators. But where there are none, it is also able to self-pollinate.

11. Indian Pipe (Monotropa uniflora)

The Indian pipe is often referred to as the ghost plant and is a member of the heather family. Although their tall, slender, waxy appearance may have you believing otherwise. It’s also totally white due to a lack of chlorophyll. That said, there are rare examples of these plants coming in a bright red color.

One of the most incredible things about the Indian pipe is that this plant doesn’t require any sunlight to grow. It’s therefore usually found in very dense forests in the temperate regions of Asia and North and South America.

The Indian pipe’s main host is the beech. But like many other species, it will actually attach to a fungus that’s connected to the tree. In this case, the plant fools the fungus into thinking it will be entering a symbiotic relationship giving nutrients in exchange for sugar where this is not the reality of the situation.

12. Broomrapes (Orobanche & Phelipanche spp.)

Broomrapes are found growing all over the northern hemisphere and are considered a pest because of how much damage they do to crops. They are known to seriously affect the yield of things like sunflowers, coconuts, palms, legumes, and a variety of vegetables such as bell peppers, tomatoes, and eggplants.

However, most species will usually only be able to attach to a single host. For example, the ivy broomrape can only parasitize ivy.

These are winter flowering plants that can grow up to 25 inches (63 cm) in height, and the flowers look very similar to that of the snapdragon.

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