FRIENDS OF EDGEWOOD NATURAL PRESERVE
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FRIENDS OF EDGEWOOD NATURAL PRESERVE
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PLANTS THAT LIKE HOSTS By Toni Corelli Visitors and docents have often asked me about the parasitic relationships some vascular plants have, especially when I talk about it in reference to the Indian warrior. In researching this relationship I found that many other plants at Edgewood also have plant/host relationships. These plants are within four families and seven genera at Edgewood (see the table at the end of this article). Parasitism for vascular plants is a relationship in which one organism uses the nutrients and water and sometimes photosynthates (carbohydrates) of another plant, the host plant. Nutrients and water are transported by thread-like haustoria produced by the root system of the parasitic plant that permeate and become embedded in the host tissue. To be a true vascular plant parasite the plant must produce haustoria. The vascular plants that produce haustoria are in two groups. Holoparasite / Obligate Group – these are nonphotosynthetic so are obligated to and must have a host to survive. They obtain water and nutrients from the host xylem and photosynthates from the host phloem. Within this group are the fleshy-stemmed holoparasites (holo = complete) in the Orobanchaceae family and the nonphotosynthetic annual vines in the Cuscutaceae family. The Orobanches are root parasites, and they have their parasitic connection with the roots of the host plant. The Cuscutas are stem parasites, and they have their parasitic connection with the stems of the host plant. Hemiparasite / Facultative Group – these are partial (hemi = half) parasites capable of both photosynthesis and parasitism and do not require a host (facultative = optional). However, in nature, when without a host they are usually smaller and not as vigorous. They obtain most of their water and nutrients from the host xylem. Our members of hemiparasites are in the Scrophulariaceae family. When the new edition of The Jepson Manual comes out in 2008, the genera listed in the table within the Scrophulariaceae family will be included in the Orobanchaceae family, based on molecular studies and their parasitic relationships. These members of the Scrophulariaceae are root parasites. Nonphotosynthetic Mycotrophic Group The coralroot orchids are not considered “true” vascular plant parasites because they do not have haustoria. They are called a nonphotosynthetic mycotrophic (myco = fungus, trophic = turning) plant. They have a symbiotic relationship with the mycorrhiza of living soil fungi and absorb carbohydrates and minerals from this fungal partner, which in turn absorbs these nutrients from the roots of nearby plants. There are various reasons why plants from several different evolutionary lines have evolved these relationships with host plants. Research has shown that parasitism in the group of holo- and hemiparasites evolved only once, but the loss of chlorophyll has occurred multiple times within the descendants of that first parasitic species. Some of the advantages of the parasitic relationship are a steady supply of water and nutrients for seed production. Although this may be a drain on the host, in most cases it does not lead to the death of the host. References Coffey, G. (2004). Indian Paintbrush: The Sunset Shades of Castilleja. Bay Nature, April-June 2004. Marvier, M.A. (1998). Parasite Impacts on Host Communities: Plant Parasitism in a California Coastal Prairie. Ecology: Vol. 79, No. 8. Mills, J.N. and Kummerow, J. (1988). Root Parasitism in Indian Paintbrush. Fremontia, Vol. 16 No. 3, October 1988. Olmstead, R.G. (2002). Whatever Happened to the Scrophulariaceae? Fremontia, Vol. 30 No. 2, April 2002. Purcell, J. (1974). Influences of Host and Environment on the Distribution and Reproductive Success of Pedicularis densiflora. Research Paper for Bio. 178 taught by Dr. Harold Mooney. Taylor, D.L. and Bruns, T.D. (1999). Population, habitat and genetic correlates of mycorrhizal specialization in the ‘cheating’ orchids Corallorhiza maculata and C. mertensiana. Molecular Ecology (1999) 8, 1719–1732 © 1999 Blackwell Science Ltd Web Pages http://www.botgard.ucla.edu/html/botanytextbooks/lifeforms/parasiticplants/ http://www.science.siu.edu/parasitic-plants/
1 Need more information what host plants are at Edgewood; information is from the literature. 2 These species are generalists and their host plants can be from other families as well. 3 Includes all species at Edgewood. |
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