No abstract

The new Smilax provides first fossil evidence of the Havanensis group and proves that this group had a western Eurasian distribution during the Miocene. The age of the fossils is in good agreement with the (molecular-based) purported split between the Havanensis and Hispida groups within Smilax. The Miocene Smilax provides evidence that all four subclades within the "New World clade" had a disjunct intercontinental distribution during parts of the Neogene involving trans-Atlantic crossings (via floating islands or the North Atlantic land bridge) and the Beringia land bridge.

Los bosques secos se consideran uno de los ecosistemas más amenazados en el trópico por las actividades antrópicas que han fragmentado y reducido el hábitat. Este estudio documentó la composición florística del bosque seco del Valle de Agalta en Honduras, con énfasis en los sitios donde habita el colibrí esmeralda (Amazilia luciae), un ave endémica y en peligro de extinción. Se colectaron datos de la estructura y composición vegetal de 265 parcelas en 35 sitios. Se identificaron 316 especies distribuidas en 76 familias y 222 géneros, que incluyen 79% eudicotiledóneas, 15% monocotiledóneas, 8% monilófitas y 1% gimnospermas. Las distribuciones vertical y horizontal indican que el bosque está dominado por individuos jóvenes. Las asociaciones vegetales más dominantes, según el índice de valor de importancia,  fueron Acacia picachensis (Fabaceae), Eugenia hondurensis (Myrtaceae) y Lysiloma acapulcense (Fabaceae). Se concluye que el Valle de Agalta aún posee bosque seco, que representa un hábitat único y es el refugio de muchas especies nativas, raras y endémicas, enlistándose algunas especies de alta prioridad de conservación.

The impacts of the historical geologic and climatic events on the diversity and genetic structure of Neotropical taxa have recently become a subject of study. However, annual plants associated with tropical dry forests remain under‐studied. The exploration of additional taxa in contrasting environments will improve the current understanding of responses of the Neotropical biota to these events. Here, we explore the species distribution and geographic structure of the annual herb Tithonia rotundifolia. We sampled 175 individuals from 19 populations of T. rotundifolia. Species distribution modelling and six microsatellite chloroplast loci were used to infer its population history. We identified areas of historical climate suitability and then tested if there is genetic structuring among these areas. Haplotypes showed strong phylogeographic structure. Historical climatic suitability areas were found along the Pacific coast; however, a gap was found at the Isthmus of Tehuantepec (IT). Although Bayesian analysis showed population structuring, amova revealed that the IT is not its main driver. Instead, a subdivision into a higher number of regions had higher FCT values. Also, populations to the east of the IT showed evidence of recent population expansion and migration in a south–north direction. Pleistocene climate fluctuations partially explain the geographic structure of T. rotundifolia. However, life‐history characteristics such as limited seed dispersal and the patchy distribution of suitable habitats explain the high haplotype diversity and population sub‐structuring and diversity. Lastly, the absence of geographic structure of some haplotypes may indicate long‐distance dispersal, or hybridisation with the closely related T. tubaeformis.