1. Cereus Miller (1754: 3088)

Type (designated by Britton & Rose 1920: 3):— Cereus hexagonus Miller (1768: Cereus no. 1).

Species richness:— The genus comprises circa 20 species (Taylor & Zappi: 269), of whick one are represented in Rio Grande do Sul, Cereus hildmannianus Schumann (1890: 202) .

General distribution:— Cereus is naturally distribuited in South America, ocurring in northern Argentina, Brazil, Bolivia, Colombia, French Guiana, Netherlands Antilles, Paraguay, Peru, Guyana, Suriname, Trinidad & Tobago, and Venezuela (Hunt et al. 2006).

Distribution in Santa Maria river basin:— In SMRB, Cereus hildmannianus is also present where (Fig. 2A), it widely distributed in the study area (Fig. 1), as well as throughout Rio Grande do Sul (Carneiro et al. 2016), which may occur in native grasslands, rocky outcrops and forests, sometimes behaving as epiphyte.

Morphologic notes:— This species characterized in having a shrubby habit (up to 8 meters high), columnar cylindrical branches, 8–12 ribbed with white-pink flowers, blooms from October to January, fruitin time shortly thereafter.