Mike Thiv

Old-New World and trans-African disjunctions of Thamnosma (Rutaceae) : Intercontinental long-distance dispersal and local differentiation in the succulent biome

PREMISE OF THE STUDY The succulent biome is highly fragmented throughout the Old and New World. The resulting disjunctions on global and regional scales have been explained by various hypotheses. To evaluate these, we used Thamnosma, which is restricted to the succulent biome and has trans-Atlantic and trans-African disjunctions. Its three main distribution centers are in southern North America, southern and eastern Africa including Socotra. METHODS We conducted parsimony, maximum likelihood, and Bayesian phylogenetic analyses based on chloroplast and nuclear sequence data. We applied molecular clock calculations using the programs BEAST and MULTIDIVTIME and biogeographic reconstructions using S-DIVA and Lagrange. KEY RESULTS Our data indicate a weakly supported paraphyly of the New World species with respect to a palaeotropical lineage, which is further subdivided into a southern African and a Horn of Africa group. The disjunctions in Thamnosma are mostly dated to the Miocene. CONCLUSIONS We conclude that the Old-New World disjunction of Thamnosma is likely the result of long-distance dispersal. The Miocene closure of the arid corridor between southern and eastern Africa may have caused the split within the Old World lineage, thus making a vicariance explanation feasible. The colonization of Socotra is also due to long-distance dispersal. All recent Thamnosma species are part of the succulent biome, and the North American species may have been members of the arid Neogene Madro-Tertiary Geoflora. Phylogenetic niche conservatism, rare long-distance dispersal, and local differentiation account for the diversity among species of Thamnosma.

Evidence for a vicariant origin of Macaronesian–Eritreo/Arabian disjunctions in Campylanthus Roth (Plantaginaceae)

The numerous disjunct plant distributions between Macaronesia and eastern Africa-Arabia suggest that these could be the relicts of a once continuous vegetation belt along the southern Tethys, which has been fragmented by Upper Miocene-Pliocene aridification. We tested this vicariance hypothesis with a phylogenetic analysis of Campylanthus (Plantaginaceae), based on nuclear and plastid DNA sequence data. Our results indicate a basal split within Campylanthus giving rise to Macaronesian and Eritreo-Arabian lineages in the Pliocene/Upper Miocene. This is consistent with the vicariance hypothesis, thus obviating the need to postulate trans-Saharan long-distance dispersal. The biogeography of Campylanthus may parallel patterns in other plant groups and the implications for our understanding of the biogeography of northern and eastern Africa, and Arabia are discussed.

How to get off the mismatch at the generic rank in African Podostemaceae

The Podostemaceae are highly enigmatic plants which are restricted to submerged river-rock habitats. The availability of new material of nine taxa from continental Africa prompted this new study. Five species belonging to the genera Dicraeanthus, Leiothylax, Letestuella, Macropodiella, and Stonesia and another four species of the large genera Inversodicraea sensu stricto and Ledermanniella sensu stricto have been analysed for the first time. New anatomical and developmental data are described and illustrated by use of microtome sections and scanning electron microscopy. In parallel, phylogenetic analyses of all available sequence data of African Podostemaceae have been conducted using three plastid markers (matK, trnD-trnT, rpoB-trnC). Inversodicraea cf. bosii appears basal within the continental African clade. The remaining taxa are distributed in three, rather poorly supported, major clades which are consistent with their morphology: (1) the Inversodicraea clade is characterised by stem scales and contains members of the former Ledermanniella subg. Phyllosoma with either pollen-monads or dyads; (2) the Ledermanniella-Monad group consisting of Leiothylax, Letestuella, Macropodiella, Stonesia, and Ledermanniella species—all taxa without stem scales but showing pollen as single grains, with Monandriellalinearifolia being basal to this clade; (3) the Ledermanniella-Dyad clade including Djinga, Dicraeanthus, and Ledermanniella species without stem scales but with pollen dyads. To reduce the polyphyly of Ledermanniella sensu lato (i.e. sensu C. Cusset) we propose restricting Ledermanniella to the species of the former subgenus Ledermanniella, resurrecting Monandriella as monotypic genus, and accepting the genus name Inversodicraea for members of Ledermanniella subg. Phyllosoma.

Eritreo-Arabian affinities of the Socotran flora as revealed from the molecular phylogeny of Aerva (Amaranthaceae)

Abstract We investigated the colonization of the Indian Ocean archipelago of Socotra through phylogenetic analysis of Aerva (Amaranthaceae) based on nuclear and plastid DNA sequence data. The biogeographic history of the genus was tracked using ancestral area reconstructions and molecular dating. Three independent colonization lineages from the Eritreo-Arabian subregion of the Sudano-Zambesian Region were revealed: one endemic clade comprising Aerva revoluta/A. microphylla and once within A. lanata and A. javanica. Our results provide further support for the dominance of Eritreo-Arabian affinities in the flora of Socotra, in contrast to more rare affinities to Madagascar, the Mascarenes, southern Africa, and tropical Asia. Our data point towards colonization via dispersal, rather than a vicariance origin of the island elements. The overall biogeographic patterns of Aerva show only limited concordance with other taxonomic groups distributed on Indian Ocean islands.

Stonesia ghoguei, Peculiar Morphology of a New Cameroonian Species (Podostemaceae, Podostemoideae)

Abstract The traditional circumscription of the genus Stonesia G. Taylor (Podostemaceae, Podostemoideae) includes three species restricted to western tropical Africa. Here, a new species, S. ghoguei E. Pfeifer & Rutishauser, is described, which represents the first Cameroonian member of the genus. There are another three Stonesia species restricted to western tropical Africa (Guinea and Sierra Leone). The genus Stonesia is characterized by capsule valves with five or seven ribs each, with the ribs nearest the sutures shorter and not reaching the ends of valves. This unique pattern is shared with the two Madagascan genera Endocaulos C. Cusset and Paleodicraeia C. Cusset. Molecular (matK) data indicate that this capsule pattern is homoplastic, occurring in Madagascar and (with Stonesia) in tropical Africa. Various characters of Stonesia (including S. ghoguei) are also found in other African podostemoids. These include flower buds inverted in the sac-like spathella; crustose roots or broad ribbons with exogenous root lobes (daughter roots); stems usually simple (rarely branched), up to 10(–40) cm long; flowers arising primarily from endogenous buds inside the stem cortex in S. ghoguei and S. fascicularis G. Taylor; and leaves repeatedly forked into narrow segments, with epiphyllous flowers arising from the clefts of these forks in S. ghoguei and S. heterospathella G. Taylor. Unlike the western African Stonesia species, S. ghoguei has pollen mainly released in monads (not only dyads), one stamen per flower with two lateral tepals (not two stamens with three tepals), and unilocular ovaries (not bilocular ones).

Molecular phylogeny and taxonomic revision of the Philippine endemic Villaria Rolfe (Rubiaceae)

The little known Rubiaceae genus Villaria is endemic mostly to the coastal forests of the Philippines. Traditionally, it has been placed in the tribe Gardenieae. Later it was transferred to Octotropideae sensu Robbrecht and Puff. Villaria was placed among the “primitive” genera of the tribe, which are essentially characterized by large fruits, horizontal ovules and numerous seeds. Parsimony and Bayesian analyses of the combined plastid (rps16 and trnT-F) dataset strongly support the inclusion of Villaria in Octotropideae as well as monophyly of the genus. However, our molecular results do not conform to the current informal groups of the tribe delimited by fruit size, ovule position, number of seeds and exotesta thickenings. Instead, a close relationship between Villaria and two “central genera” (Hypobathrum and Pouchetia) is revealed for the first time. This clade is sister to a group comprising “primitive” (Fernelia), “advanced” (Kraussia and Polysphaeria) and “central” (Feretia) representatives. In addition, our combined tree strongly supports a sister taxa relationship between Canephora and Paragenipa. Villaria is characterized by unilocular ovaries, parietal placentation and strictly horizontal ovules. These features are unique within the Octotropideae. We recognize a total of five Villaria species, one new species (V. leytensis) is described here, and two species (V. philippinensis and V. rolfei) are transferred into synonymy with V. odorata. Each species is fully described, and a key to the species, a distribution map and illustrations are provided.

A phylogenetic study of Echidnopsis Hook. f. (Apocynaceae-Asclepiadoideae) - taxonomic implications and the colonization of the Socotran archipelago

We investigated the phylogeny, taxonomy and biogeography of the Eritreo-Arabian genus Echidnopsis Hook. f. (Apocynaceae-Asclepiadoideae). Phylogenetic reconstructions based on nrITS sequence data were obtained using maximum likelihood and parsimony analyses. The results reveal two weakly supported clades, each with a mix of African and Arabian taxa, including the genus Rhytidocaulon, and with four Socotran species forming a subclade of their own. Rather than a vicariance origin of these island elements, our data suggest a single dispersal event from eastern Africa. Echidnopsis thus parallels biogeographic patterns found for other Socotran endemic plants. Our revised taxonomy recognizes 28 species and 4 subspecies in the genus. Two new combinations, E. planiflora subsp. chrysantha and E. sharpei subsp. bavazzani are proposed.

A Morphological Cladistic Analysis of Gentianaceae-Canscorinae and the Evolution of Anisomorphic Androecia in the Subtribe

Abstract We investigated cladistic relationships among the genera and species of paleotropical Gentianaceae-Canscorinae using morphological characters. Twenty-five characters were scored across all 23 species of the subtribe plus four outgroup species representing the closely related Coutoubeinae and Chironiinae. The maximum parsimony analysis resulted in one most parsimonious tree of 91 steps. The seven genera of Canscorinae fall into two major clades. These comprise Cracosna, Hoppea, Schinziella, and Canscora (clade I), and Microrphium, Phyllocyclus, and Duplipetala ined. (clade II). Intergeneric relationships were highly congruent with earlier molecular analyses in which, however, not all genera were included. Phylogenetic relationships among genera imply that the two different types of anisomorphic androecia found in Canscorinae evolved independently. An ancestral area analysis showed that Canscorinae are likely to have originated in SE Asia. From there India was colonized by the Canscora, Hoppea, Schinziella clade. The presence of some species of this clade in Africa/Madagascar is considered to be the result of independent long-distance dispersal events. Communicating Editor: Gregory M. Plunkett

Spatial and ecological population genetic structures within two island-endemic Aeonium species of different niche width

Abstract The Crassulacean genus Aeonium is a well‐known example for plant species radiation on oceanic archipelagos. However, while allopatric speciation among islands is documented for this genus, the role of intra‐island speciation due to population divergence by topographical isolation or ecological heterogeneity has not yet been addressed. The aim of this study was to investigate intraspecific genetic structures and to identify spatial and ecological drivers of genetic population differentiation on the island scale. We analyzed inter simple sequence repeat variation within two island‐endemic Aeonium species of La Palma: one widespread generalist that covers a large variety of different habitat types (Ae. davidbramwellii) and one narrow ecological specialist (Ae. nobile), in order to assess evolutionary potentials on this island. Gene pool differentiation and genetic diversity patterns were associated with major landscape structures in both species, with phylogeographic implications. However, overall levels of genetic differentiation were low. For the generalist species, outlier loci detection and loci–environment correlation approaches indicated moderate signatures of divergent selection pressures linked to temperature and precipitation variables, while the specialist species missed such patterns. Our data point to incipient differentiation among populations, emphasizing that ecological heterogeneity and topographical structuring within the small scales of an island can foster evolutionary processes. Very likely, such processes have contributed to the radiation of Aeonium on the Canary Islands. There is also support for different evolutionary mechanisms between generalist and specialist species.

A taxonomic revision of Canscora, Cracosna, Duplipetala, Hoppea, Microrphium, Phyllocyclus and Schinziella (Gentianaceae–Canscorinae)

A taxonomic revision of all genera belonging to Gentianaceae–Canscorinae, i.e., Canscora, Cracosna, Duplipetala, Hoppea, Microrphium, Phyllocyclus and Schinziella is presented, including keys to the taxa, distribution maps and seed coat descriptions. One new genus, one new species and seven new combinations are described. In total seven genera and 23 species are recognized. All taxa are of palaeotropical distribution with centres in India and SE Asia.