Character evolution and biogeography of Casearia (Salicaceae): Evidence for the South American origin of a pantropical genus and for multiple migrations to the Caribbean islands

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 and South American taxa, is not sufficiently resolved internally, to allow biogeographic conclusions. The Old World clade of Casearia provides another example for a late Laurasian migration starting in the Neotropics

Caracterización de la estructura poblacional de Phyllanthus orbicularis (Phyllanthaceae) en la Sierra de Cajálbana, La Palma, Pinar del Río, Cuba

Phyllanthus orbicularis Kunth is an endemic plant from Cuba of the Phyllanthaceae family, which lives on the serpentine soils from Pinar del Río to the surroundings of the city of Holguín and Antilla. In the xeromorphic shrubs on serpentine soils, it is a dominant species, which could indicate that it has achieved a great evolutionary success in the colonization of this habitat. In this work, the population structure of the Managed Floristic Reserve "Cuabales de Cajálbana", La Palma, Pinar del Río, was characterized. A systematic sampling consisted of 10 plots of 2m x 2m (4m2), arranged every 5m and changing direction every two plots was made. In each plot, the total number of individuals was recorded and each individual was measured for height, diameter of the base and coverage of the crown. State classes were established based on the values of the height and diameter of the base. The population density was of 5.25 (± 3.53) individuals/m2 and the pattern of spatial arrangement was clustered that is the characteristic of the shrub species. Individuals were observed in all state classes determined for the characterization of the population, which holds its stability in the study area and showed a high percentage of recruitment, which guarantees its maintenance over time.Phyllanthus orbicularis Kunth es una planta endémica de Cuba de la familia Phyllanthaceae, que habita sobre los suelos de serpentina desde Pinar del Río hasta los alrededores de la ciudad de Holguín y Antilla. En los matorrales xeromorfos sobre serpentinas, es una especie dominante, lo que podría indicar que esta ha alcanzado un gran éxito evolutivo en la colonización de este hábitat. En este trabajo se caracterizó la estructura poblacional de la Reserva Florística Manejada “Cuabales de Cajálbana”, La Palma, Pinar del Río. Se realizó un muestreo sistemático que constó de 10 parcelas de 2m x 2m (4m2), dispuestas cada 5m y cambiando de dirección cada dos parcelas. En cada parcela se registró el total de individuos y a cada individuo se le midió la altura, diámetro de la base y la cobertura de la copa. Se establecieron clases de estado a partir de los valores de la altura y el diámetro de la base. La densidad poblacional fue de 5,25 (± 3,53) individuos/m2 y el patrón de arreglo espacial resultó agregado que es el característico de las especies arbustivas. Se evidenciaron individuos en todas las clases de estado establecidas para la caracterización de la población, lo que demuestra que es estable en el área de estudio y que presenta un alto porcentaje de reclutamiento, lo que garantiza su mantenimiento en el tiempo