Sunday, November 25, 2007

Details on Common Species

There a thousands of parasitic plant species, but here are a few common ones you may have heard of.

Mistletoe: Mistletoes are parasitic plants that grow on the branches of shrubs and trees. Nearly all mistletoes are hemiparasites with evergreen leaves that perform photosynthesis and berries in a variety of colors.


(Above we see clusters of mistletoe invading a large group of trees.)



The name "mistletoe" incorporates a multitude of species, including Desert Mistletoe (Phoradendron californicum), Dwarf Mistletoe (Arceuthobium campylopodum), and the species we are familiar with, Eastern Mistletoe (Phoradendron serotinum).

Mistletoes grow on a wide variety of hosts and can eventually prove fatal, although they usually only stunt growth. While most plants have a root that grows downward (gravitropism), mistletoe roots, along with other parasitic plants, have roots that grow in the direction of their host.

Mistletoe seeds are generally spread by birds which eat the berries and later excrete them onto trees and shrubs. The seeds are coated with a sticky substance that hardens and attaches the seed to its future host. While most plant seeds germinate in the soil, mistletoe seeds germinate directly on the branches they are attached to.

Dodder: Dodder is a thin and wispy plant, usually orange or yellow (occasionally tinged with purple or red.) The stems are threadlike and short. When dodder flowers they are usually white, pink, or yellowish. A few species include California Dodder (Cuscuta californica) and Salt Marsh Dodder (Cuscuta salina).

Dodder is parasitic to various kinds of wild and cultivated plants, especially alfalfa, closer, and potatoes. Dodder is difficult to "weed out" because its seeds are often mixed in with those of the farmed crops.

Dodder absorb water, minerals, and carbohydrates from the host through its haustoria. In dodder, the haustoria are modified adventitious roots. When dodder produce seeds, they germinate the next growing season if a host is present. However, if there is not, the seeds can remain dormant for up to five years, waiting for their opportune moment. Once the seeds germinate, they must find a host within a few days or else they die.

Wood rose: Wood rose (New Zealand) is a fully parasitic plant (holoparasite). It's a root parasite in the family Balanophoraceae. It's New Zealand's only fully parasitic flowering plant. It has no green leaves or shoots of its own.

The small flowers which make up the large buds (inflorescences) are adapted to attract bats which then pollinate the plant. Wood rose is also often pollinated by mice and rats. These inflorescences are extremely skewed in gender ratio as there are five male "flowers" for each female.

Wood rose's latin name is Dactylanthus taylorii and it is also known as "the flower of Hades." When wood rose invades its host, usually a shrub or tree, the host's roots enlarge in repsonse. As the roots enlarge, the wood rose creates a solid attachment, and from then on gains its nutrients though this connection.

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