New records of the rare North American endemic Chara brittonii (Characeae), with comments on its distribution

Abstract

Characeae is a family of freshwater green algal macrophytes found on every continent except Antarctica. Although some species are thought to be cosmopolitan, others appear to be restricted to relatively small geographic areas. Chara brittonii is a North American endemic previously reported from eight scattered populations in Indiana, Michigan, New Jersey, and Ohio. Given that few extant populations were known, basic questions about its distribution, habitat preference, morphology, and phylogenetic placement remained unanswered. We have surveyed every reported locality for C. brittonii except the New Jersey locality, because the collection details are vague, and also surveyed numerous additional waterbodies in Indiana, Michigan, and Wisconsin. We have found extant populations in nine localities in three states. These include one newly reported site in Indiana and five newly reported sites in Wisconsin, the first known populations in that state. Chara brittonii seems to have been extirpated from several historical sites in recent decades. We expanded both the range and the number of known extant populations for C. brittonii and hypothesize that C. brittonii may be more widespread in the Midwest than previously thought. Factors contributing to the actual and apparent rarity of this species are discussed including its preferred habitat and small size. We observed that the number of antheridial scute cells of C. brittonii varied from 4–8 with both triangular and elongate scutes produced on the same thallus, an unusual condition for the family. Phylogenetic analyses using three plastid-encoded markers placed C. brittonii among a paraphyletic grade of C. foliolosa sensu lato strains in the monophyletic subsection Willdenowia. We propose that C. foliolosa, as currently recognized, represents a species complex of several phylogenetically distinct lineages, and conclude that C. brittonii is a structurally and phylogenetically distinct species worthy of conservation.