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.
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