Frustules are heterovalvar. Valves are linear to linear-elliptic. The valve apices may be narrowed, rounded, or subrostrate. The axial area is narrow on both raphe and rapheless valves. The striae are composed of biseriate rows of circular areolae on both valves. The raphe valve has an asymmetric fascia. The rapheless valve lacks a fascia, or any other central expansion.
Lemnicola is monotypic; the genus was erected for the single species, Lemnicola hungarica (Grun.) Round and Basson. The species had previously been considered within Achnanthidium or Achnanthes. Living cells have single, plate-like plastids. Cells grow as epiphytes on the aquatic angiosperms Lemna and Wolfia.