Orthoseira roeseana

Frustules are heavily silicified and aligned in short filaments of 2-10 cells adjoined face-to-face by short conical or flattened spines. The spines are regularly spaced along the face-mantle junction. Frustules are 39.7-51.1 µm long in the pervalvar axis. The base of the spines extend onto the mantle and may continue for a short distance onto the valve face. The mantle is broad. In smaller cells, the mantle height is relatively larger. Valves have a flat to slightly convex face. Valves have a small central area with 2-5 carinoportulae, a type of pore specific to the genus Orthoseira. Valve face areolae are arranged in radial striae that end in small furrows formed by adjacent spine bases near the face-mantle junction. Valve face areola density is 14.5-19.3 in 10 µm. The valve mantle has straight pervalvar striae (16.4-19.3 in 10 µm) with areola density 13.5-17.5 in 10 µm. Frustules with a broad cingulum. Girdle bands are variably ornamented with pervalvar rows of fine areolae.

The genus Orthoseira is recognized as needing monographic treatment to resolve the typification, taxonomy, and nomenclature of its common forms—roeseana, dendroteres, dendrophila, tatrica, circularis, americana, epidendron (Houk 1993, 2003, Spaulding and Kociolek 1998), which is complicated by the great morphologic variation within current taxa. Here, we follow the broad concept taxonomy for O. roeseana of Houk (2003).