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Nickrent,Daniel L. Department of Plant Biology, Southern Illinois University, Carbondale, Illinois.
- Molecular phylogenetics
- Molecular evolution
- Related Primary Literature
- Additional Reading
Although not generally recognized, parasitic organisms make up a large percentage of the Earth's total biodiversity. The word “parasite” generally conjures up images of organisms such as microbes and worms, but this life-form has evolved repeatedly in many groups, including flowering plants (angiosperms). A parasitic angiosperm is one that attaches to a host root or stem via a modified root called the haustorium, thereby deriving some or all of its water and nutrients. Some parasitic plants are green and photosynthetic, but they still obtain water and solutes from their host. These are called hemiparasites (somewhat of a misnomer in that they are fully parasitic). Other parasitic plants have lost their ability to conduct photosynthesis and are thus fully heterotrophic (that is, obtaining nourishment from exogenous organic matter). These are called holoparasites, and they obtain carbohydrates from host phloem as well as water from the host xylem. Here a plant is considered parasitic only if it forms a direct haustorial connection to a host plant. This excludes plants such as Indian pipe (Monotropa) that attach to mycorrhizal fungi and are technically known as mycoheterotrophs.
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