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Abstract

Hydrophyllum brownei Krai & Bates (Browne's waterleaf), newly described in 1991, is endemic to the Ouachita Mountain Natural Division of Arkansas. For the purpose of better understanding population parameters within which H. brownei grows, ranges of shade values, population extents, and population distance relationships to streams were measured. Hydrophyllum brownei grows in extremely high shade, in populations of widely varying sizes, and always in association with a stream system. In order to list species associated with H. brownei, vouchers of species assemblages were collected at the H. brownei sites visited. The species is designated as critically imperiled globally because of its extreme rarity (Gl). It is also extremely rare in Arkansas (Si) according to NatureServe and the Arkansas Natural Heritage Commission. Previously unknown populations were discovered in this study, and a recommendation to lower species rarity rank is made. However, based upon information gathered about population parameters, it is recommended that the species be reduced in status only to the global rank of G2 (imperiled globally because of rarity) and the state rank of S2 (very rare). Hydrophyllum brownei is currently known from 26 distinct sites, nine of which were discovered in 2002. Because H. brownei is a rare endemic to the Ouachita Mountains, continued intermittent monitoring of its populations is advised.

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