Poaceae Barnhart na serra do Cachimbo, Amazônia oriental, Brasil.

Abstract

Poaceae Barnhart is one of the largest families of monocotyledons, with 11,500 species, 700 genera and 12 subfamilies. In Brazil, 1490 species in 226 genera are recorded, of this total, 500 species and 122 genera occur in the Amazon. It is a family of economic and ecological importance, occurring in several ecosystems of the world, especially in open formations. In the Amazon, although forests are dominant, open areas are found, and their characterization is hindered by discrepancies in terminology and lack of studies on plant communities, especially in ecotonal regions. The Serra do Cachimbo is located in the Amazon-Cerrado transition, with specific soil and altitude characteristics, and a gradient rainforests, savannas and grasslands habitats, which are conducive to both richness and endemism of grasses, including bamboos. However, it is a poorly studied region and has suffered in recent decades with disordered population growth, illegal burning and advancing pastures. In this context, floristic-taxonomic studies are essential for systematizing knowledge on biodiversity and clarifying ecological and evolutionary processes. The aim of the dissertation was to carry out a floristic study of the Poaceae (focusing on the taxonomy of the subfamily Bambusoideae) in the Serra do Cachimbo. The study area is located between Pará and Mato Grosso states; it has three protected areas: Parque Estadual do Cristalino (MT), Reserva Biológica Nascentes da Serra do Cachimbo (PA) and Campo de provas Brigadeiro Velloso (PA). Two field expeditions are carried out in 2019 and 2021, covering the units in Pará. In addition to the samples collected, we examined the specimens of 18 national and international herbaria that have collections of grasses from Serra do Cachimbo. The dissertation is structured in two distinct chapters: the first presents a checklist with habitat data, along with comments on the geographic distribution of endemic and invasive species. 124 species was found, distributed in 54 genera and seven subfamilies. Panicoideae (93) and Bambusoideae (16) are the most diverse subfamilies, follow by Chloridoideae (9), Aristidoideae (3), Anomochlooideae (1), Micrairoideae (1) e Oryzoideae (1). The richest genera were Paspalum (19), Panicum (8), Trichanthecium (8) and Axonopus (7). Three species are recorded for the first time in the Mato Grosso state and 13 in the Pará, of these, eight are new occurrences for the Amazon. Two species are being analyzed and are possibly new species to science. The second chapter presents a taxonomic study of bamboos. 16 species and nine genera were found, four species constitute new state records and two are possibly new species. Morphological descriptions, identification keys, geographic distribution and habitat data, taxonomic comments and photographs are presented. Despite the high diversity of grasses when compared to other Amazon agrostological checklists, only a small part of the area was sampled. A more in-depth study is needed to uncover the knowledge gaps in the flora.