Novelties in Dimerostemma (Asteraceae, Heliantheae) from Rio Grande do Sul, Brazil

Revisiting the Dimerostemma collection in Rio Grande do Sul, the southernmost state of Brazil, one new species of Dimerostemma is described and another is resurrected. Although previously synonymized under Dimerostemma arnottii , Dimerostemma oppositifolium is here resurrected based on its distinct opposite leaves, linear to lanceolate leaf limbs, and specific pappus scale measurements. Additionally, Dimerostemma ramboi is described as a new species endemic to the state of Rio Grande do Sul. It resembles D. arnottii but is distinguished by its opposite leaves (sometimes whorled at the apex), subcordate to rounded leaf bases, and shorter floral structures, such as the ray floret tube and pappus aristae. We provide morphological descriptions, photo plates, its distribution is mapped, and preliminary conservation status for both taxa. Furthermore, an identification key and an occurrence map for the seven species of Dimerostemma now recognized for Rio Grande do Sul are presented.