Monographs Details: Phormidium autumnale var. minus
Authority: Gardner, Nathaniel L. 1927. New Myxophyceae from Porto Rico. Mem. New York Bot. Gard. 7: 1-144. pl. 1-23.
Description:Species Description - Trichomes 3.6-4 µ diam., slightly tapering at the apices and slightly uncinate; cells quadrate to twice as long as broad; apical cell blunt-conical. This form marks the lowest limit of the species in diameter of the trichome. The cells average longer than in the species, and the apical cell is conical instead of rounded-capitate.

Distribution and Ecology - Growing among other algae in a water reservoir at the Experiment Station, Rio Piedras, no. 203, type. Growing in a waterfall between Arecibo and Utuado, no. 1460, type.