Monographs Details: Calothrix simplex N.L.Gardner
Authority: Gardner, Nathaniel L. 1927. New Myxophyceae from Porto Rico. Mem. New York Bot. Gard. 7: 1-144. pl. 1-23.
Family:Rivulariaceae
Description:Species Description - Filaments 200-250 µ long, attached at the base, erect and straight or a few curved close to the base and erect, forming a continuous stratum with other Myxophyceae, tapering gradually and uniformly from the basal cell to the long apical hair, or in some of the oldest filaments, 2-4 basal cells somewhat larger, making a slight bulbous base, up to 18 µ diam. at the base 2-2.5 µ at the apex; trichomes 10-14 µ diam. at the base, aeruginous, not constricted at the dissepiments; cells one-third to one-fourth the diameter long, homogeneous; heterocysts single, all basal, hemispherical to elongated, hyaline; sheath thin, firm, smooth, homogeneous, hyaline; reproduction by small hormogonia formed in the upper part of the filament.

Species Description - Growing in a stream on stones in the vicinity of San Lorenzo, no. 501, type; in a pool about four kilometers north of Mayagüez, no. 1327 c; on stones in the Turabo River near Caguas, no. 481.

Discussion:

PLATE 13, FIGURE 19

The material of this collection is very clean and in excellent condition. Apparently every stage in the development is represented. There are many small hormogonia down at the base of the mature specimens. Between these small specimens and the old mature ones there are many gradations in size represented.

The species is associated with Lyngbya erecta, a species attached at one end and the filaments erect and parallel. Together these form a compact, velvety stratum on stones.