NEIDIUM ALPINUM VAR. QUADRIPUNCTATUM (HUSTEDT) COMB. NOV., AN IMPORTANT ACIDOBIONTIC TAXON FROM NORTHEASTERN NORTH AMERICA

Abstract

Navicula quadripunctata Hustedt, which has sometimes been synonymized with Neidium alpinum Hustedt, is distinct and recognized here as Neidium alpinum var. quadripunctatum (Hustedt) Hamilton, comb. nav. This taxon is distinguished from the nominate variety by its robust size, elliptical-linear shape, and narrowly rounded apices (length: 12–33 μm width: 3–7 μm; striae 30–38 in 10 μ). From SEM observations, it is evident that the bifurcate appearance of the terminal raphe fissures corresponds to a siliceous flap that covers the polar raphe endings, which are simple and straight. N. alpinum var. quadripunctatum is acidobiontic, commonly found in lakes and streams of pH 4.5–5.9. In North America, this diatom has been found in Ontario (Canada) and Alaska, Michigan, Minnesota, New Hampshire, New York, Pennsylvania and Wisconsin (U.S.A.).