Stauroneis alabamae

Valves are large and rhombic, with small specimens more elliptical lanceolate. Valve margins are slightly undulate near the apices. Apices are subcapitate.

Striae are parallel to slightly radiate near the stauros, becoming strongly radiate approximately halfway between the stauros and the apices and nearly parallel near the apices. In SEM images, it can be resolved that the striae immediately bordering the apex are convergent. Areolae are irregularly spaced throughout the center of the valve, but are evenly spaced near valve margins. A row of areolae borders the axial area.

The stauros is narrow and linear, and in some specimens constricted near the valve margins. Axial area is slightly expanded near the apices and broadens slightly as it meets the axial area.

The raphe is lateral. The proximal raphe ends are slightly expanded. The distal raphe ends are sickle shaped.

In SEM, it can be seen that the helictoglossa closely resembles the internal view of a rimoportula. The pseudoseptum is small occurring only as a small silica extension on one side of the raphe.

The differences between S. alabamae and S. alabamae var. angulata are currently unclear, and should be investigated when the Hustedt collection becomes accessible again.

Additional notes: In the original line drawing, S. alabamae var. angulata is depicted as being smaller than S. alabamae var. rostrata (=Stauroneis baconiana) and bears radiate striae bordering the stauros.

Stauroneis nobilis has historically been associated with S. alabamae. This association appears to have originated with Cleve's 1894 description of Stauroneis anceps var. nobilis, which was cited by Heiden in 1903. This association was perpetuated by Cleve-Euler (1953), then by Hustedt (1959), followed by Patrick and Reimer (1966), and most recently by Krammer and Lange-Bertalot (1986). However, as noted by Cleve in 1894, the original description clearly states that S. nobilis bears decussate striae. Further work should clarify the relationship of these large taxa.