Monographs Details: Calothrix evanescens 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 erect or prostrate, straight or curved, rigid, 200-300 µ long, 7-8 µ diam.; trichomes cylindrical from the basal heterocyst throughout the larger portion of the length, then tapering to a very narrow, short hair, constricted at the dissepiments, 5.5-6.8 µ diam.; cells cylindrical to dolioform, quadrate to one-third the diameter long, mostly homogeneous, pale aeruginous to yellowish or honey-color, mostly showing a clear central area; cross-walls relatively thick and conspicuous; apical cell blunt and rounded, becoming conical in the young stage of growth; the apical portion soon prolonged into a short hair; heterocysts single, basal, spherical to subspherical, same diameter as the trichome; sheath thin, firm, smooth, homogeneous, hyaline, vanishing at about half way from the base to the apex.

Distribution and Ecology - Growing in water among other Myxophyceae and debris, Jayuya, no. 1776 a, type; on a wall, Coamo Springs, no. 411.

Discussion:

PLATE 13, FIGURE 22

In certain stages in the life cycle of this species it resembles the genus Microchaete. The hair dies back, the apical portion becomes dolioform, the terminal cell enlarges and becomes rounded, and a sheath is secreted. The whole trichome is then cylindrical with but a single basal heterocyst. When growth begins at the apex, the diameter begins to diminish, the apical cell becomes conical, and finally a short hyaline hair is produced. It is a very distinct species, related in some of its characters to C. linearis.