LAUSR

The genus Aulacoseira is cosmopolitan and often abundant in fresh waters. In Costa Rica, freshwater diatom surveys have been restricted to flowing waters, aside from our own explorations. Among sediment samples from some 90 lakes we have encountered an undescribed species which we herein propose to name Aulacoseira umanai Haberyan sp. nov. In this species, the face of larger valves often bears ridges and tubercles (knobs); separation spines are short (<2.3 µm) and longer spines are absent. The ringleiste is thick, solid, and very wide. This, in combination with its short collum, distinguishes A. umanai from many other species of the genus. Aulacoseira umanai is abundant in the surficial sediments of multiple glacial lakes that are over 3450 m in elevation on Cerro Chirripó; it is also abundant in glacial-age deposits in La Chonta bog (2310 m a.s.l.). It seems to have evolved from an ancestor that resembled A. alpigena; the locality of this event is unknown but was likely to have been a high-altitude lake in the Central American isthmus.