Recent debates on the number of plant species in the vast lowland rain forests of the Amazon have been based largely on model estimates, neglecting published checklists based on verified voucher data. Here we collate taxonomically verified checklists to present a list of seed plant species from lowland Amazon rain forests. Our list comprises 14,003 species, of which 6,727 are trees. These figures are similar to estimates derived from nonparametric ecological models, but they contrast strongly with predictions of much higher tree diversity derived from parametric models. Based on the known proportion of tree species in neotropical lowland rain forest communities as measured in complete plot censuses, and on overall estimates of seed plant diversity in Brazil and in the neotropics in general, it is more likely that tree diversity in the Amazon is closer to the lower estimates derived from nonparametric models. Much remains unknown about Amazonian plant diversity, but this taxonomically verified dataset provides a valid starting point for macroecological and evolutionary studies aimed at understanding the origin, evolution, and ecology of the exceptional biodiversity of Amazonian forests.Amazonia | floristics | rain forests | seed plants | species diversity

The cataloging of the vascular plants of the Americas has a centuries-long history, but it is only in recent decades that an overview of the entire flora has become possible. We present an integrated assessment of all known native species of vascular plants in the Americas. Twelve regional and national checklists, prepared over the past 25 years and including two large ongoing flora projects, were merged into a single list. Our publicly searchable checklist includes 124,993 species, 6227 genera, and 355 families, which correspond to 33% of the 383,671 vascular plant species known worldwide. In the past 25 years, the rate at which new species descriptions are added has averaged 744 annually for the Americas, and we can expect the total to reach about 150,000.

Casearia (Salicaceae) is a pantropical genus of circa 200 species, around half of which dwell in the Neotropics. Despite the availability of phylogenetic studies that suggest that Casearia sensu Sleumer is not monophyletic, a strong phylogenetic framework was still lacking for this genus. We tested the monophyly of Casearia and examined the relationships of its species to other taxa of the tribe Samydeae, including Laetia, Samyda and Zuelania, which recently have been sunk into Casearia, as well as Euceraea, Lunania, Neoptychocarpus, Ryania and Tetrathylacium. We further put a focus on the Neotropical taxa since Casearia and allies are speciose both on the Caribbean islands and adjacent mainlands, thus providing an interesting group to address the origin of the Caribbean and Cuban flora. Our phylogenetic analyses based on four combined rapidly evolving plastid regions (petD, rpl16, rps4-trnT-L-F, trnK-matK-psbA) as well as nuclear ITS revealed Casearia as monophyletic with high support, including not only the former members of Laetia, Samyda and Zuelania but also Euceraea and Neoptychocarpus. Casearia is constituted by several major clades, mostly being entirely Neotropical, one of which exclusively comprises species endemic to the Caribbean islands. Another clade, which includes all Palaeotropical species, is nested among Neotropical lineages. Our divergence date estimates using the plastid dataset and fossil calibration points in Salicaceae indicate that the Casearia crown group started to diversify during the late Eocene, approximately 39 Ma. The stem of the Old World clade diverged from Neotropical ancestors around 27 Ma, in the Oligocene. We used BayesTraits to reconstruct the evolution of seven characters commonly used to define Casearia and allied genera. We found morphological characters, such as branched inflorescences (fasciculate, glomerulous, cymose) or uniseriate stamen series, that work well to circumscribe the genus, whereas dioecy, which was used to diagnose Neoptychocarpus, or higher stamen numbers (>12), found in Laetia and Zuelania, are homoplastic in Salicaceae, the latter character derived within Casearia from ancestors with 7-12 stamens. Pellucid dots appear to have evolved earlier than the divergence of the Casearia clade in Samydeae, and were lost in Ryania and Tetrathylacium, and thus are no synapomorphy for Casearia. In order to establish a monophyletic genus concept for Casearia, we propose to also merge Euceraea and Neoptychocarpus. Our reconstruction of ancestral areas using BioGeoBears indicate that South America is the ancestral area of Casearia. From there, multiple migrations occurred to Mesoamerica and the Caribbean islands. The Caribbean that comprises nearly all Caribbean endemics started to diversify around 9.5 Ma. Our trees depict C. corymbosa, which exhibits significant infraspecific phylogenetic structure for the sampled Mexican and Colombian individuals, as the sister to the Caribbean clade. The other clade, with Cuban endemics (C. ternstroemioides) but also Mesoamerican a...

The origin of Neotropical species diversity is strongly associated with the geological history of South America. Since the Miocene, a number of species radiations across different Neotropical lineages coincided with the rise of the Andes and the formation of the Isthmus of Panama. The species-rich genus Philodendron Schott (Araceae) is widely distributed across Neotropical rainforests, originating in the Late Oligocene and diversifying more intensely from the Miocene onward. It is likely that its diversification process and distribution patterns are associated with recent geological changes in the Americas. To test this hypothesis, we sampled the species diversity of Philodendron across its entire geographic range and used a combination of three non-coding plastid regions (petD, rpl16, and trnK/matK) to obtain a comprehensive time-calibrated phylogeny. We then inferred geographic range evolution and explored the impact of the Andean orogeny on speciation, extinction, and dispersal. The genus Philodendron originated ~29 million years ago (mya) and experienced the earliest diversification events ~25 mya in the Pan-Amazonian rainforests. From the Middle Miocene onward, multiple geographic range expansion events occurred from Amazonia to southeast Brazil and to the area which would become the Chocó and the northern Andes. From the Pliocene onward, Philodendron reached Central America and the Caribbean islands, and Andean lineages recolonized and diversified in Amazonia. In Philodendron, higher diversification rates are found in the adjacent lowland rainforests of the northern Andes compared with other regions in the Neotropics, demonstrating a potential indirect impact of the Andean uplift on species radiations in lowland regions.