Time-Calibrated Phylogenies of Hummingbirds and Hummingbird-Pollinated Plants Reject a Hypothesis of Diffuse Co-Evolution

Neotropical ecosystems house levels of species diversity that are unmatched by any other region on Earth. One hypothesis to explain this celebrated diversity invokes a model of biotic interactions in which interspecific interactions drive diversification of two (or more) lineages. When the impact of the interaction on diversification is reciprocal, diversification of the lineages should be contemporaneous. Although past studies have provided evidence needed to test alternative models of diversification such as those involving abiotic factors (e.g., Andean uplift, shifting climatological regimes), tests of the biotic model have been stymied by lack of evolutionary time scale for symbiotic partners. In this study, we infer timescales for diversification of hummingbirds and a species-rich plant lineage that is ~50% hummingbird pollinated, Ruellia (Acanthaceae). Results demonstrate that hummingbirds originated about 20 million years before New World Ruellia and that all but one major hummingbird clade was extant before the plant group originated. Thus, the classic model of “diffuse co-evolution” between hummingbirds and this group of plants is rejected by our data. However, together with the observation that the Neotropical clade of Ruellia (~350 species) is far more species rich than its Old World sister group (~75 species), our results are consistent with the hypothesis that plant diversification in the Neotropics has been facilitated in part by a pre-existing diversity of hummingbirds. This hypothesis may find support in other lineages of Neotropical plants that similarly exhibit asymmetrical partitioning of species diversity in the Paleo- vs. Neotropics

Nelsonioideae (Lamiales: Acanthaceae): Revision of Genera and Catalog of Species

A taxonomic account of Acanthaceae subfamily Nelsonioideae based on morphological and phylogenetic data treats five genera with 172 species: Anisosepalum (3), Elytraria (21), Nelsonia (2), Saintpauliopsis (1), and Staurogyne (145). Two other currently recognized genera, Gynocraterium and Ophiorrhiziphyllon, are included within Staurogyne, and the new combinations, Staurogyne guianensis and S. macrobotrya, are proposed. Probable apomorphic and other diagnostic macro- and micromorphological characters are discussed relative to the subfamily and genera. Characters of the inflorescence, androecium (especially pollen), and seed show important phylogenetic and diagnostic signal. A key to genera, generic descriptions and discussions, illustrations, and distribution maps are provided. Lists of currently recognized species for each genus include synonymies and distributions by country

Phylogeny of Dyschoriste (Acanthaceae)

The pantropical and poorly known genus Dyschoriste (Acanthaceae) is sister to Strobilanthopsis within subtribe Petalidiinae. The present study included 38 accessions of 28 species as sources of DNA data for one nuclear (nrITS) and four chloroplast (intergenic spacers: psbA-trnH, trnS-trnG, ndhF-rpl32, rpl32- trnL(uag)) regions to provide an estimate of the phylogeny of the genus. We found that Dyschoriste is strongly supported as monophyletic inclusive of Apassalus, Chaetacanthus, and Sautiera. Within Dyschoriste, three geographically cohesive lineages were recovered with moderate to strong support: a mainland African clade, a Caribbean and southeastern United States clade, and a South and Central America clade. A third New World clade composed of accessions from the south central through southwestern US to Mexico is weakly supported and corresponds to the D. linearis species complex recognized by previous researchers (six of the ten taxa putatively part of this complex were sampled). A second Old World clade unites taxa from across the Old World tropics (mainland Africa, Madagascar and southeast Asia). Some aspects of relationships among these main clades were unresolved or not strongly supported, and two Old World taxa, south Asian D. dalzellii and the wide-ranging D. nagchana, were not placed with confidence in any of these clades. The simplest explanation for the current distribution of the genus is that there was a single dispersal event of Dyschoriste from the Old to the New World, with a subsequent radiation in the New World

New Species, New Combinations and New Synonymies Towards a Treatment of Acanthaceae for the Manual de Plantas de Costa Rica

In preparation for the publication of the Manual de Plantas de Costa Rica, new species, names, combinations, and synonymies are provided in six genera of Acanthaceae: Anisacanthus, Chamaeranthemum, Dicliptera, Justicia, Ruellia and Stenostephanus. The new species are A. grace-woodiae, J. altior, J. lithophila and S. chavesii. A new name at the species level, R. leonardiana, is provided for R. tubiflora var. hirsuta. With Habracanthus, Hansteinia, Kalbreyeriella and Razisea being subsumed within Stenostephanus, the new combinations S. blepharorhachis, S. citrinus, S. leiorhachis (= Razisea spicata non S. spicatus), S. strictus, S. ventricosus, S. villosus and S. wilburii are formalized. Seven new synonymies are presented for species of Chamaeranthemum, Dicliptera, Justicia and Stenostephanus, as well as lectotypifications in the first and latter two genera

Three New Species of Aphelandra (Acanthaceae) from Central America

Volume: 69Start Page: 402End Page: 41

Systematics and Reproductive Biology of the Central American Species of the Aphelandra pulcherrima Complex (Acanthaceae)

Volume: 71Start Page: 104End Page: 16

Data from: A rich fossil record yields calibrated phylogeny for Acanthaceae (Lamiales) and evidence for marked biases in timing and directionality of intercontinental disjunctions

More than a decade of phylogenetic research has yielded a well-sampled, strongly supported hypothesis of relationships within the large (> 4,000 species) plant family Acanthaceae. This hypothesis points to intriguing biogeographic patterns and asymmetries in sister clade diversity but, absent a time-calibrated estimate for this evolutionary history, these patterns have remained unexplored. Here, we reconstruct divergence times within Acanthaceae using fossils as calibration points, experimenting both with fossil selection and effects of invoking a maximum age prior related to the origin of Eudicots. Contrary to earlier reports of a paucity of fossils of Lamiales (an order of ~23,000 species that includes Acanthaceae) and to the expectation that a largely herbaceous to soft-wooded and tropical lineages would have few fossils, we recovered 51 reports of fossil Acanthaceae. Rigorous evaluation of these for accurate identification, quality of age assessment, and utility in dating yielded eight fossils judged to merit inclusion in analyses. With nearly 10 kilobases of DNA sequence data, we used two sets of fossils as constraints to reconstruct divergence times. We demonstrate differences in age estimates depending on fossil selection and that enforcement of maximum age priors substantially alters estimated clade ages, especially in analyses that utilize a smaller rather than larger set of fossils. Our results suggest that long-distance dispersal events better explain present-day distributions than do Gondwanan or northern land bridge hypotheses. This biogeographical conclusion is for the most part robust to alternative calibration schemes. Our data support a minimum of 13 Old World to New World dispersal events but, intriguingly, only one in the reverse direction. Eleven of these 13 were among Acanthaceae s.s., which comprises > 90% of species diversity in the family. Remarkably, if minimum age estimates approximate true history, these 11 events occurred within the last ~20 million years even though Acanthaceae s.s is over three times as old. A simulation study confirmed that these dispersal events were significantly skewed towards the present and not simply a chance occurrence. Finally, we review reports of fossils that have been assigned to Acanthaceae that are substantially older than the lower Cretaceous estimate for Angiosperms as a whole (i.e., the general consensus that has resulted from several recent dating and fossil-based studies in plants). This is the first study to reconstruct divergence times among clades of Acanthaceae and sets the stage for comparative evolutionary research in this and related families that have until now been thought to have extremely poor fossil resources