Plant Structure, Function, and Use

Plant Responses to Stimuli

Can plants be parasitic?

Yes, plants can be parasitic, obtaining nutrients from, and thus harming, other plants. The link between parasites and their hosts is called a haustorium. In many plants, the link is one or more xylem-to-xylem connections between the two plants. The parasitic plant depends largely on the evaporation of water from its leaves as a means of pulling nutrient-containing water from the xylem of its host. In addition, the stomata of many parasitic plants always remain at least partially open, even at night, ensuring a continuous supply of nutrients from the host. For example, cancer root (Orobanche uniflora) parasitizes hardwood trees; trees such as sandalwood (genus Santalum) obtain their nutrients from nearby grasses.

Many parasitic plants lack chlorophyll and cannot carry out photosynthesis, and thus they depend entirely on their host for nutrients. In some cases, the presence of chlorophyll does not guarantee an independent lifestyle. For example, mistletoe (genus Phoradendron) and witchweed (genus Striga) are green, yet grow only as parasites. The green portions of these parasites contain only small amounts of certain enzymes required in photosynthesis.


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