Monographs Details: Nostoc ellipsoideum 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 without definite form, usually flattened and irregular, firm-gelatinous or cartilaginous up to 3 mm. diam.; trichomes moderately tortuous, not densely congested, pale aeruginous, deeply constricted at the dissepiments; cells cylindrical to narrowly ellipsoidal, 1.4-1.8 µ diam., quadrate to 2.2 times as long as the diameter, homogeneous; hetorocysts dolioform, 2.4-2.8 µ diam.; spores ellipsoidal, about 3 µ diam., about 6 µ long; tegument opalescent, changing to yellowish brown at maturity.

Distribution and Ecology - Growing on rocks in the vicinity of Jayuya, no. 1797, type.

Discussion:Nostoc ellipsoideum appears to have its nearest affinities in Humifusa section of the genus. The spores seem not to be quite mature.