Bory 1927 Category: Monoraphid TYPE SPECIES: Achnanthes adnata
Bory The frustules of Achnanthes are heterovalvar. The raphe
valve usually possesses a central area of thickened silica,
called a fascia or stauros. The rapheless valve has no such
central area and the sternum may be positioned near the valve
margin. In girdle view, the mantle of the rapheless valve
appears to be more ornamented than that of the raphe valve. The
striae are uni-, bi-, or triseriate and composed of areolae
covered by complex cribra, or sieve plates. Cells may grow
alone, or may form short chains. Living cells are usually
attached to substrata by a mucilage stalk extending through one
end of the raphe valve. Most species are found in marine
habitats, but a few taxa occur inland including Achnanthes
coarctata. Inland species are commonly associated with mosses
and lichens in aerophillic habitats. Many common species
previously classified in this genus are now recognized as
species of Achnanthidium, Psammothidium, Planothidium, and oth