TaxonomyRead full entry
Comments: Classification reviewed by B.L. Turner (1995, Phytologia 79: 10-12); Kartesz (1999) apparently follows this treatment. Turner treats this species in the genus Hedyotis as H. nigricans; it has also been called Houstonia nigricans. He recognizes six varieties, of which one is widespread in both the U.S.A. and in Mexico (var. nigricans), and five others are localized, and mutually allopatric but often generally sympatric with the widespread variety. Two of these varieties (var. floridana and var. pulvinata) occur in Florida, with var. floridana also in the Bahamas; two (var. austrotexana and var. papillacea) occur in Texas, with var. papillacea also in New Mexico; and one (var. gypsophila) is endemic to Mexico, known primarily from Nueva Leon.