Parasitic plants

 

Parasitic plants

Some parasitic plants can be beneficial to the ecosystem they live in. The most well-known parasitic plant is the mistletoe, the plant that has been part of Christmas celebrations in western cultures for hundreds of years. A branch of mistletoe is hung at the top of a doorway or suspended from the ceiling. Couples who “happen” to cross each other’s paths under the mistletoe are permitted a kiss. For each kiss, a berry is plucked off the branch. When the berries run out, so do the kisses. You didn’t know mistletoe was a parasite? Most people don’t. The name “mistletoe” (originally “mistiltan”) most likely comes from the Anglo-Saxon words “mistel” meaning “dung,” and “tan” meaning “twig.” So that makes the real name for this plant “dung-on-a-twig.” The dung in question comes from birds. Birds eat the berries, and some of their dropping fall on tree branches. Mistletoe seeds happen to be very sticky, so they quickly adhere to the branch. When the seeds germinate, they can grow for a while in the bird dropping, as if it was dirt. As quickly as they can, though, the baby mistletoe plants start putting out special “roots” called haustoria (hoe-STORE-ee-ah). The haustoria somehow grow their way through the tree’s bark and get into the sapwood where the living xylem and phloem tubes are. They put their thin root-like tubes into the tree’s xylem and phloem, as if putting a drinking straw into someone else’s glass. The mistletoe slurps away, sucking water, minerals and sugars from the tree’s vascular system. Thus, the mistletoe is permanently attached to a tree, instead of growing in the ground. The mistletoe is what botanists called a hemiparasite (“hemi” meaning “halfway”). The leaves can still do photosynthesis, so it is not completely reliant on the host tree. At first, the tree hardly notices the mistletoe and isn’t especially bothered by it. If rainfall is adequate, there is enough water for both plants. However, as the mistletoe grows larger and larger, there is a greater possibility that the tree won’t be able to keep up with the increasing demands the mistletoe places on it. Some trees do eventually die from mistletoe invasion, and, in general, gardeners see mistletoe as a threat. They usually prune off any tree branches that show mistletoe infestation.