3. Frailea Britton & Rose (1922: 208)

Type (designated by Britton & Rose 1922: 210):— Frailea cataphracta Britton & Rose.

Species richness:— Frailea comprises 19 species according to Gerloff (2001). Twelve are endemic, recognized only for Rio Grande do Sul State (Pontes et al. 2018).

General distribution:— Frailea has a restricted geographical distribution to southern Brazil, Paraguay, Uruguay, southeastern Bolivia, and northeast Argentina.

Distribution in Santa Maria river basin:— In SMRB occur nine species, Frailea albifusca, (Fig. 2C and Fig. 2F), F. castanea Backeberg (1936: 415) (Fig. 2D), F. lepida Buining & Brederoo (1973: 106), (Fig. 2E), F. mammifera, (Fig. 2G), F. pumila (Lemaire 1838: 21) Britton & Rose (1922: 209) (Fig. 2H), F. pygmaea (Spegazzini 1905: 497) Britton & Rose (1922: 210) (Fig. 2I), F. erythracantha R.Pontes, A.S.Oliveira & Deble (2018: 202) (Fig. 2J), in the study area, these species usually grow on rocky outcrops.

Morphologic notes:— They are tiny plants less than 4 cm in diameter, sometimes solitary, globular to cylindrical. Undeveloped ribs and very small straight or curved thorns. Flowers very ephemeral, l cleistogamous or casmogamous, yellow or cream-yellow, dense woolly floral bracts and many bristles. Dried fruit with many seeds up to 1.5 cm long. They usually bloom in summer and fruit soon after.