ABSTRACT
Inundations in Amazonian black-water river floodplain result in the selection of different tree lineages, thus promoting coexistence between species. We investigated whether Amazonian tree communities are phylogenetically structured and distributed along a flooding gradient from irregularly flooded forests along streams embedded within upland (terra-firme) forest to seasonally flooded floodplains of large rivers (igapós). Floristic inventories and hydrological monitoring were performed along the Falsino River, a black-water river in the eastern Amazon within the Amapá National Forest. We constructed a presence-and-absence matrix and generated a phylogeny using the vascular plant database available in GenBank. We calculated the standardized values of the metrics of phylogenetic diversity (ses.PD), average phylogenetic distance (ses.MPD), and average nearest-neighbor distance (ses.MNTD) to test whether the history of relationships between species in the community is influenced by inundation. We used the phylogenetic endemism (PE) metric to verify the existence of taxa with restricted distribution. Linear regressions were used to test whether phylogenetic metrics have a significant relationship with the variables: maximum flood height, maximum water table depth, and maximum flood amplitude. The results show that forests subject to prolonged seasonal flooding have reduced taxon richness, low phylogenetic diversity, and random distribution of lineages within communities. On the other hand, terra-firme riparian forests showed higher rates of taxon richness, diversity, and phylogenetic dispersion, in addition to greater phylogenetic endemism. These results indicate that seasonal and predictable soil flooding filters tree lineages along the hydrographic gradient. Different adaptations to root waterlogging are likely requirements for colonization in these environments and may represent an important factor in the diversification of tree lineages in the Amazon biome.
ABSTRACT
We carried out a comparative morphological study to evaluate the taxonomic value of seed and seedling traits of Entada polystachya and E. simplicata (Leguminosae, Mimosoideae, Mimoseae). Seeds of both species were collected from wild populations in Roraima State, Brazil. Our results show consistent quantitative and qualitative differences between these species regarding their seeds and seedlings. Testa fracture lines, funiculus impression, lens characters, radicle shape and length, and cotyledon lobes length, seedling morphology group, number of pinnae at first node, and hypocotyl length permit a straightforward distinction of E. polystachya from E. simplicata, supporting a recent treatment of the latter taxon as a distinct species, endemic to Roraima State, northern Amazonia, Brazil.
Este trabalho apresenta um estudo morfológico comparativo para avaliar o valor taxonômico de caracteres de semente e plântula de Entada polystachya e E. simplicata (Leguminosae, Mimosoideae, Mimoseae). As sementes de ambas as espécies foram coletadas de populações no Estado de Roraima, Brasil. Os resultados evidenciaram consistentes diferenças qualitativas e quantitativas entre estas espécies, com relação as suas sementes e plântulas. Linhas de fratura na testa, impressão do funículo, caracteres da lente, forma e comprimento da radícula e comprimento dos lobos dos cotilédones, grupo morfológico de plântula, número de pinas no primeiro nó eofilar e comprimento do hipocótilo permitem uma separação entre E. polystachya e E. simplicata, providenciando apoio a um recente reconhecimento do último táxon como uma espécie distinta, endêmica no Estado de Roraima, Norte da Amazônia, Brasil.
