Reinterpreting the phylogenetic position, systematics and distribution of the Raddia-Sucrea lineage (Poaceae, Olyrinae), with a new monotypic and endangered herbaceous bamboo genus from Brazil

Herbaceous bamboos (tribe Olyreae) are typical components of Neotropical forests, with a great diversity in Brazil. Olyreae comprise three subtribes, of which Olyrinae are the most heterogeneous, with 19 genera widely distributed in Brazilian biomes but also occurring in Mexico, Central America and northern and western South America. One of the lineages of this group is composed of the genera Raddia and Sucrea, the relationships of which were recently studied. Although Raddia was clearly monophyletic, the three Sucrea spp. displayed incongruence between the plastid and nuclear genomes. In the present study, we increased taxon sampling and included additional DNA regions [ITS, rpl32-trnL, trnD-trnT and trnS-(psbZ)-trnG] and used macro- and micromorphological characters to investigate the relationships in this group. The analyses involved maximum parsimony, Bayesian inference and maximum likelihood estimation methods. The three species traditionally assigned to Sucrea are confined to the Brazilian Atlantic Forest and represent two lineages, one sister to Raddia and composed of S. monophylla (the type species) and S. maculata, with open panicles, microechinate-areolate pollen and a distribution from Bahia to Rio de Janeiro states. The other lineage, sister to Raddia + Sucrea, is composed of an unusual species with contracted panicles, microechinate-rugulate pollen and conspicuous tuberous roots; this is endemic to Rio de Janeiro and Espirito Santo states. This species, traditionally known as S. sampaiana, is here transferred to the new genus Brasilochloa (as B. sampaiana). It is a rare lineage, currently endangered with extinction, as is the case for a number of herbaceous bamboos occurring in the Atlantic Forest.