DIDYMODON NEVADENSIS, A NEW SPECIES FOR NORTH-AMERICA, WITH COMMENTS ON PHENOLOGY

Didymodon nevadensis Zand. is described as a new taxon from North Amer ica, reported from southern British Columbia, southern Nevada, norther n Texas, and southern Chihuahua. The new species is distinguished from its closest relative (D. brachyphyllus (Sull.) Zand = D. reedii Robin s., syn. nov.) by the absence of a conical cell ending the costa, a wi der costa at midleaf than below, the presence of a characteristic bulg ing ventral costal pad of cells, costal guide cells in two layers, and leaf margins loosely revolute. Study of extensive populations at the type locality in southern Nevada showed that this species is confined there to gypsiferous ridges and is presently represented only by femal e plants.