Are There Cannibalistic Plants?

Animals turn cannibalistic for a variety of reasons – hunger, lack of mates, competition for territory – to name a few. But have you ever heard of cannibalistic plants? There are carnivorous plants for sure. But are there plants that love their veggies? Turns out, yes there are. 

When scientists discovered that plants could be carnivorous, they were shocked. The discovery just went against the grain. But when they found out that plants could get cannibalistic too; it was a discovery that they just couldn’t wrap their heads around.

When plants eat their kin

When we talk about cannibalism in plants, we talk about plants which use other plants as food/prey as a parasite would its host.

The most fundamental way of segregating all parasitic plants is looking at how they function. Some parasitic plants affect the prey’s xylem (tissues near the roots), while others attack the prey’s phloem (tissues near the leaves). These plants grow hook-like ‘roots’ called haustoria, which they use to hang onto their hosts. The haustoria are also used to absorb nutrients from the host plants.

Dodder, aka cuscata, is a type of stem parasite that creeps and climbs around the stems and leaves of plants, biting into the plant using its haustoria and sucking out its juices. Hydnora is a root parasitic plant that sinks its haustoria into the roots of its prey, draining the plant of all its nutrients and juices.

Image: Hydnora; a carnivorous plant that feeds on insects also happens to be a parasitic plant. It’s a root parasite that feeds off other plants as a secondary food source.

Parasitic plants and photosynthesis

Another way of segregating parasitic plants is to understand whether they photosynthesize or not. In this case, there are two types of parasitic plants:

• Holoparasites

Holoparasitic plants are a nightmare for gardeners around the world. These are non-photosynthesizing parasitic plants which rely solely on feeding-off other plants. They are extremely dangerous to plant health and some species lead to 100% mortality in the affected population if care isn’t taken to get rid of them.

Squawroot

Toothwort

Luckily, holoparasitic plants are quite ‘friendly’ to gardeners. They take a very long time to dry out their hosts, which gives gardeners and nursery caretakers plenty of time to tackle them. The dodder is a great example of a holoparasitic plant that is completely dependent on its host for nutrition.

Other holoparasites are squawroot, toothwort, broomrape and beechdrop.

Image: Types of holoparasitic and hemiparasitic plants. Obligate parasites rely completely on their hosts to reproduce and will die out if they can’t find a permanent host to reproduce on; facultative parasites can reproduce as individual plants and don’t necessarily need a host plant to reproduce (although it can help if they have a permanent host).

• Hemiparasites

Hemiparasitic plants derive food in two ways. They photosynthesize and gain valuable nutrition from the sun and soil just like any other plant. But they also leech-off neighbouring plants as parasites.

Since hemiparasitic plants also photosynthesize, they don’t actively feed-off other plants. It is only when they are unable to get nutrients from the sun and soil or they stand the chance of getting better nutrients from other plants that they turn parasitic.

Indian Paintbrush

Velvetbell

Examples of hemiparasitic plants are mistletoe, Indian sandalwood, rattle plants, Indian paintbrush and velvetbells.

Parasitic plants and symbiotic relationships

Finally, the third way of segregating parasitic plants is to understand their relationship with their prey. Myco-heterotrophs are plants that appear to have a parasitic-symbiotic relationship with other plants.

A great example is the relationship between orchids and fungi. The orchids tap into the fungi’s mycorrhizal networks (tubular, filament-like structures that connect fungi to each other and other plants underground) and steal water, minerals and nutrients from the fungi.

Myco-heterotrophs can be either hemiparasitic or holoparasitic and despite masquerading as a symbiotic host, they add no visible value to the fungi.

The curse of the Vampire

Parasitic, cannibalistic plants do not root anywhere. Instead, the seeds look for a host and latch onto the host using the haustoria. A few days after feeding-off their host, the plants begin to voraciously multiply. Soon, the parasites grow to such an extent that they completely cover up their hosts and take over the neighbouring population. The food source is soon sucked dry and killed.

Image: Dodder plant growth after months of parasitic feeding. The host plant will soon be completely covered and killed.

This feature of parasitic plants has earned them their scary title – The Vampire Plants.

-NISHA PRAKASH

P.S: Featured Image: Vampire Plant