Monographs Details: Nostoc sphaerosporum N.L.Gardner
Authority: Gardner, Nathaniel L. 1927. New Myxophyceae from Porto Rico. Mem. New York Bot. Gard. 7: 1-144. pl. 1-23.
Description:Species Description - Thallus spherical or in part irregular in form when young, becoming more irregular with age; up to 600 µ diam.; trichomes moderately flexuous and intricate, not densely crowded, becoming straighter when spore formation begins, 3-3.6 µ diam., pale aeruginous; heterocysts spherical, 6-6.5 µ diam., hyaline; spores spherical, 4.7-5.5 µ diam., smooth, hyaline; tegument dirty white, moderately firm.

Distribution and Ecology - Growing on bark among other Myxophyceae near Utuado, no. 1506 a, type.

Discussion:The diminutive size of the colonies coupled with the spherical spores, heterocysts, and cells, constitute a combination of characters distinctive of this species.