Two New Rare, Endangered Species of Stenandrium (Acanthaceae: Acantheae) Reinforce Proposed Centers of Endemism and Key Biodiversity Areas in the Serra do Espinhaço, Brazil

We describe and illustrate Stenandrium diamantinense and Stenandrium eustachyum, two new species from campos rupestres in a region of high endemism in southeastern Brazil. Stenandrium diamantinense is differentiated from other congeners by its unique indurate, small leaves with revolute margins. Stenandrium eustachyum is most similar to Stenandrium villosum, the only congener with which it shares the combination of oval bracts and caulescent habit; it can be distinguished from the latter species by its ovate to widely ovate leaves (vs. lanceolate in S. villosum). Stenandrium eustachyum differs from other species of Stenandrium from the Serra do Espinhaco by its oval (vs. linear in all other regional species) bracts. Photographs of living plants in the field are supplemented by scanning electron micrographs of pollen, seeds, and trichomes. A distribution map and a key to the Stenandrium species of the southern Serra do Espinhaco are provided. Stenandrium diamantinense is informally and provisionally assessed as Endangered and S. eustachyum as Critically Endangered. The distribution of Stenandrium in the Serra do Espinhaco supports proposed centers of endemism and key biodiversity areas.