More info for the term: rootstock
Purple loosestrife is a non-native, perennial wetland herb [14,129]. Stems are erect, 1 to 8 feet (0.3-2.4 m) tall, becoming woody with age and persisting through winter and up to 2 years [9,14,73,118]. Mature, long-established plants are often 10 feet (3 m) tall and 5 feet (1.5 m) wide . Plants may become increasingly bush-like by producing greater numbers of basal stems from the same rootstock each year [14,79,118,129]. Plants begin producing multiple stems from a single rootstock as early as the 2nd growing season . Anderson  recorded single genets with over 130 stems produced from a single rootstock during a single season. He also estimated ages for individual plants up to 22 years. Observations have been recorded of particular rootstocks failing to generate shoots during a given year, but producing aboveground growth during each prior and subsequent season .
Leaves are 2 to 6 inches (5-14 cm) long and attached close to the stem . Flower spikes vary in length from > 40 inches (1 m) to only a few inches, and only 2 to 3 inches (5.1-7.6 cm) of the spike typically display open flowers at any given time [9,73]. Fruits are capsules 2-3 mm in length . Seeds measure approximately 400 x 200 microns, and weigh approximately 1.8 x 10-6 ounces (50 Âµg) per seed, which is comparatively quite small among North American temperate wetland plants [116,129].
Seedlings quickly develop a thick, hardened taproot . Mature plants subjected to persistent flooding respond by forming aerenchymous (containing large intercellular air spaces) tissue, permitting oxygen flow to submerged roots .
The preceding description provides characteristics of purple loosestrife that may be relevant to fire ecology and is not meant to be used for identification. Keys for identifying purple loosestrife are available in various floras (e.g. [57,71]). Photos and descriptions of purple loosestrife are also available online from Minnesota Sea Grant. Check with the native plant society or cooperative extension service in your area for more information.
- 1. Anderson, Mark G. 1991. Population structure of Lythrum salicaria in relation to wetland community structure. Durham, NH: University of New Hampshire. 93 p. Thesis. 
- 9. Balogh, Gregory Robert. 1986. Ecology, distribution, and control of purple loosestrife (Lythrum salicaria) in northwest Ohio. Columbus, OH: Ohio State University. 122 p. Thesis. 
- 14. Benefield, Carri. 2000. Lythrum salicaria L. In: Bossard, Carla C.; Randall, John M.; Hoshovsky, Marc C., eds. Invasive plants of California's wildlands. Berkeley, CA: University of California Press: 236-240. 
- 56. Hickman, James C., ed. 1993. The Jepson manual: Higher plants of California. Berkeley, CA: University of California Press. 1400 p. 
- 57. Hitchcock, C. Leo; Cronquist, Arthur. 1973. Flora of the Pacific Northwest. Seattle, WA: University of Washington Press. 730 p. 
- 73. Levin, Donald A.; Kerster, Harold W. 1973. Assortative pollination for stature in Lythrum salicaria. Evolution. 27: 144-152. 
- 79. Mal, Tarun K.; Lovett-Doust, Jon; Lovett-Doust, Lesley; Mulligan, G. A. 1992. The biology of Canadian weeds. 100. Lythrum salicaria. Canadian Journal of Plant Science. 72(4): 1305-1330. 
- 102. Rawinski, Thomas James. 1982. The ecology and management of purple loosestrife (Lythrum salicaria L.) in central New York. Ithaca, NY: Cornell University. 88 p. Thesis. 
- 111. Shamsi, S. R. A.; Whitehead, F. H. 1974. Comparative eco-physiology of Epilobium hirsutum L. and Lythrum salicaria L. I. General biology, distribution and germination. Journal of Ecology. 62(79): 272-290. 
- 116. Shipley, B.; Parent, M. 1991. Germination responses of 64 wetland species in relation to seed size, minimum time to reproduction and seedling relative growth rate. Functional Ecology. 5(1): 111-118. 
- 118. Skinner, Luke C.; Rendall, William J.; Fuge, Ellen L. 1994. Minnesota's purple loosestrife program: history, findings, and management recommendations. Special Publication 145. St. Paul, MN: Minnesota Department of Natural Resources, Division of Fish and Wildlife, Ecological Services Section. 27 p. 
- 129. Thompson, Daniel Q.; Stuckey, Ronald L.; Thompson, Edith B. 1987. Spread, impact, and control of purple loosestrife (Lythrum salicaria) in North American wetlands. Fish and Wildlife Research 2. Washington, DC: U.S. Department of the Interior, Fish and Wildlife Service. 55 p. 
- 71. Larson, Gary E. 1993. Aquatic and wetland vascular plants of the Northern Great Plains. Gen. Tech. Rep. RM-238. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 681 p. Jamestown, ND: Northern Prairie Wildlife Research Center (Producer). Available: http://www.npwrc.usgs.gov/resource/plants/vascplnt/vascplnt.htm [2006, February 11]. 
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