No abstract

Aim Using the Acalyphoideae, we explore the origin and diversification of the Caribbean flora. This lineage of flowering plants constitutes an important component of the flora of the Caribbean islands with many endemics. Furthermore, because it is also diverse in adjacent Mexico, Mesoamerica and South America, it allows a representative analysis of possible migration routes into the Caribbean. Location Neotropics, Cuba, Hispaniola and the Caribbean region, Mexico and Mesoamerica. Methods We generated a well‐resolved and dated phylogenetic hypothesis based on a dense sampling, in particular of the New World taxa but also representing all remaining Acalyphoideae, and combined datasets of chloroplast spacers and introns. Bayesian divergence‐time estimation was applied to determine node ages. Ancestral states of distributional areas were reconstructed in a Bayesian framework to determine the geographical origin of the Caribbean ancestors. Results A Neotropical clade started to diversify 59.29 [50.41–68.44 95% highest posterior density (HPD)] Ma within the Acalyphoideae. The Caribbean islands then were reached several times independently from the Miocene onwards. The exclusively Caribbean Leucocroton–Lasiocroton–Garciadelia [9.1 (6.3–12.3 95% HPD) Ma] and Acidoton–Platygyna [9.3 (5.2–15.4 95% HPD) Ma] clades exhibit one of the most successful plant radiations in the region, and Caribbean subclades of Acalypha and Bernardia just date back to the Pliocene and Pleistocene, respectively. Main conclusions Our data show that Mexico and Mesoamerica have played a key role as a source for today's Caribbean Acalyphoideae. Their ancestors arrived from the mainland to the Caribbean islands during the Miocene when Caribbean land masses were completely separated and then diversified in situ. We postulate long‐distance dispersal to have played a major role for colonizing the Caribbean.

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...

Cubanthus (Euphorbiaceae) has traditionally been recognized as a small genus of three similar species restricted to Cuba and Hispaniola. In this study we used DNA sequence data from the nuclear ITS and chloroplast ndhF gene regions to investigate its systematic position and the position of four other shrubby Euphorbia species endemic to Cuba: E. cubensis, E. helenae, E. munizii, and E. podocarpifolia. The results demonstrate that all of these taxa belong to a well-supported Antillean clade nested within Euphorbia that also includes E. punicea and E. gymnonota. For that reason, we treat Cubanthus as a section of Euphorbia instead of a separate genus. Euphorbia sect. Adenorima is relegated to a synonym of sect. Cubanthus. New names are proposed for Cubanthus brittonii and Cubanthus linearifolius (Euphorbia millspaughii and E. scutiformis, respectively), and a new combination is made for Cubanthus umbelliformis (Euphorbia umbelliformis). Section Cubanthus belongs to clade C of Euphorbia and is part of a New World assemblage that includes members of sections Euphorbiastrum, Pteroneurae, Portulacastrum, Stachydium, and the former genus Pedilanthus. Based on both the molecular results and morphological differences, two subsections are proposed: subsect. Cubanthus and subsect. Moa. The molecular phylogeny supports the hypothesis that section Cubanthus radiated entirely within the Antilles and the nearby Bahamian archipelago.

The new genus Saxiloba is described with the two species S. firmula from the Caribbean and S. hawaiiensis from Hawaii. Saxiloba is characterized by a unique, placodioid thallus forming distinct lobes, growing on rock in shaded to exposed situations with a trentepohlioid photobiont and a fenestrate thallus anatomy with distinct surface lines. The material is often sterile, but Porina-like perithecia and ascospores had previously been described for the Caribbean taxon and were here confirmed for both species. Molecular sequence data also confirmed placement of this lineage in Porinaceae. Its position within that family supports the notion that Porinaceae should be subdivided into a larger number of genera than proposed in previous classification attempts. Compared to other Porinaceae, Saxiloba exhibits a unique morphology and anatomy that recalls taxa in the related family Graphidaceae and it substantially expands the known phenotypic variation within Porinaceae. The two recognized species are similar in overall morphology but, apart from their disjunct distribution and different substrate ecology, differ in lobe configuration, color and disposition of the crystal clusters and resulting surface patterns.