Parasites
Parasitic plants Dodder Parasitic plants derive all or part of their water and nutrition from another plant. Parasitic plants may be classified as being a holoparasite or a hemiparasite. Holoparasitic plants produce no chlorophyll and are totally reliant on the host plant. Dodder (Cuscuta) is a holoparisite, while mistletoe (Phoradendron) is a hemiparisite. Mistletoe Hemiparasitic plants derive some of their nutrition for the host plant, but produce chlorophyll and are functionally photosynthetic. Back to plant growth form menu Next Back to vegetative parts main menu Main menu Parasitic plants Parasitic plants may also be grouped as to whether they attach to the root or stem system of the host plant. Broomrapes (Orbanache sp.) is a genus of over 200 species of root-attached holoparasites. Back to plant growth form menu Back Next The orange flowers belong to the stemattached hemiparasite (Psittacanthus) on a hardwood tree in Costa Rica. Back to vegetative parts main menu Main menu Parasitic plants Parasitic plants attach to the host plant’s stem or root through a specialized structure called a haustorium. This creates a direct connection between the vascular systems of the two plants. Dodder (Cuscuta) Back to plant growth form menu Back Next Back to vegetative parts main menu Main menu Parasitic plants Parasitic plants must produce seeds that can germinate in close proximity to their hosts. Seeds in the root parasite group are able to chemically identify when a host plant is close and trigger germination. Stem parasites tend to produce fruits that attract birds to move them from host tree to host tree as in mistletoe. The fruits contain a mucilage (called viscin) that helps stick the seed to the stem prior to germination. Lysiana exocarpi Back to plant growth form menu Mistletoe (Phoradendron) Back Next Back to vegetative parts main menu Main menu Parasitic plants Parasitic plants may associate with a number of host plants or they may be very specific about the host plants they colonize. Juniper mistletoe (Phorodendron juniperinum) colonizes junipers in western North America. Back to plant growth form menu Back Next Dwarf mistletoe (Arceutholium sp.) colonizes several conifers, including pines, spruce and firs. Back to vegetative parts main menu Main menu Parasitic plants Root-attached parasites In root holoparasitic plants, the only above ground growth is usually the flowers. Lathraea Orobanche Purple toothwort (Lathraea clandestina) is a root holoparasitic plant with an attractive floral display. It is parasitic on alder and willows as evidenced by the spent willow flowers around the plant. Back to plant growth form menu Back Next Naked broomrape (Orobanche uniflora) is a root holoparasite from the relatively large broomrape family. Back to vegetative parts main menu Main menu Parasitic plants Root-attached parasites Beechdrops (Epifagus americana) is a holoparasitic plant specific to beech (Fagus) tree roots. Beechdrops have the interesting behavior of producing open (chasmogamous) crosspollinating flowers at the top of the inflorescence and closed (cleistogamous) self-pollinating flowers at the base of the inflorescence. Back to plant growth form menu Back Next Back to vegetative parts main menu Main menu Parasitic plants Root-attached parasites By definition, holoparasites are also obligate parasites, because they can not exist without their host plant association. Squawroot (Conopholis americana) is a root holoparasite on oak (Quercus). Back to plant growth form menu Back Next Northern ground cone (Boschniakia rossica) is a root holoparasite on alder (Alnus). Back to vegetative parts main menu Main menu Parasitic plants Root-attached parasites Indian paintbrush (Castilleja) is an example of an obligate hemiparasitic plant. It produces functional photosynthetic leaves, but is still reliant on its host plant to grow successfully. They mainly colonize grass species. Indian paintbrush (Castilleja) Back to plant growth form menu Back Next Back to vegetative parts main menu Main menu Parasitic plants Root-attached parasites Pedicularis are also obligate root-attached hemiparasitic plants. Elephant’s head grows in moist areas in the Rocky Mountains and is named after the shape of the flower. Other Pedicularis have the common name lousewort. They are not very specific about their host plants. Back to plant growth form menu Lousewort (Pedicularis) Back Next Elephant’s head flower (Pedicularis groenlandicum) Back to vegetative parts main menu Main menu Parasitic plants Root-attached parasites Some hemiparasitic plants, like these false foxgloves, can grow without a parasitic host association. They are considered facultative parasites, but in nature they usually retain a parasitic association with a host plant. Yellow false foxglove (Aureolaria virginica) Back to plant growth form menu Back Next False foxglove (Agalinis ) Back to vegetative parts main menu Main menu Parasitic plants Root-attached parasites Sandlewood is an example of a woody plant that is a root hemiparasitic plant. Santalum lanceolatum Back to plant growth form menu Back Next Back to vegetative parts main menu Main menu Parasitic plants Shoot-attached parasites A major group of shoot parasites are characterized as mistletoes. These are aerial obligate hemiparasites. Phoradendron californicum Back to plant growth form menu Back Next Phoradendron leucarpum Back to vegetative parts main menu Main menu Parasitic plants Shoot-attached parasites Shoot parasite flowers vary from being small and inconspicuous to very showy. Phoradendron Back to plant growth form menu Santalum Back Next Psittacanthus Back to vegetative parts main menu Main menu Parasitic plants Shoot-attached parasites Following seed germination, an attachment at the tip of the radicle called a holdfast attaches to the stem until the haustorial root can penetrate through the bark and into the stem. Mistletoe seedlings Back to plant growth form menu Back Next Back to vegetative parts main menu Main menu Parasitic plants Shoot-attached parasites Some shoot parasites produce adventitious epicortical roots that coil or travel along the host plants stem and eventually establish additional haustorial connections. Haustorium Epicortical roots Epicortical root Dendropemon Back to plant growth form menu Back Next Back to vegetative parts main menu Main menu Parasitic plants Shoot-attached parasites Dodder (Convulvulaceae) and Laurel dodder (Lauraceae) are examples of vining holoparasites. They form multiple haustorial connections as the stems elongate and twist around the host. Haustoria Dodder (Cuscuta) Laurel dodder (Cassytha) Back to plant growth form menu Back Back to vegetative parts main menu Main menu
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