J.S. Boatwright

Causes of Plant Diversification in the Cape Biodiversity Hotspot of South Africa

The Cape region of South Africa is one of the most remarkable hotspots of biodiversity with a flora comprising more than 9000 plant species, almost 70% of which are endemic, within an area of only ± 90,000 km2. Much of the diversity is due to an exceptionally large contribution of just a few clades that radiated substantially within this region, but little is known about the causes of these radiations. Here, we present a comprehensive analysis of plant diversification, using near complete species-level phylogenies of four major Cape clades (more than 470 species): the genus Protea, a tribe of legumes (Podalyrieae) and two speciose genera within the iris family (Babiana and Moraea), representing three of the seven largest plant families in this biodiversity hotspot. Combining these molecular phylogenetic data with ecological and biogeographical information, we tested key hypotheses that have been proposed to explain the radiation of the Cape flora. Our results show that the radiations started throughout the Oligocene and Miocene and that net diversification rates have remained constant through time at globally moderate rates. Furthermore, using sister-species comparisons to assess the impact of different factors on speciation, we identified soil type shifts as the most important cause of speciation in Babiana, Moraea, and Protea, whereas shifts in fire-survival strategy is the most important factor for Podalyrieae. Contrary to previous findings in other groups, such as orchids, pollination syndromes show a high degree of phylogenetic conservatism, including groups with a large number of specialized pollination syndromes like Moraea. We conclude that the combination of complex environmental conditions together with relative climatic stability promoted high speciation and/or low extinction rates as the most likely scenario leading to present-day patterns of hyperdiversity in the Cape.

Extinction risk and diversification are linked in a plant biodiversity hotspot

Plant extinction risks in the Cape, South Africa differ from those for vertebrates worldwide, with young and fast-evolving plant lineages marching towards extinction at the fastest rate, but independently of human effects.

Symbiotic diversity, specificity and distribution of rhizobia in native legumes of the core Cape Subregion (South Africa)

Rhizobial diversity and host preferences were assessed in 65 native Fynbos legumes of the papilionoid legume tribes Astragaleae, Crotalarieae, Genisteae, Indigofereae, Millettieae, Phaseoleae, Podalyrieae, Psoraleeae and Sesbanieae. Sequence analyses of chromosomal 16S rRNA, recA, atpD and symbiosis-related nodA, nifH genes in parallel with immunogold labelling assays identified the symbionts as alpha- (Azorhizobium, Bradyrhizobium, Ensifer, Mesorhizobium and Rhizobium) and beta-rhizobial (Burkholderia) lineages with the majority placed in the genera Mesorhizobium and Burkholderia showing a wide range of host interactions. Despite a degree of symbiotic promiscuity in the tribes Crotalarieae and Indigofereae nodulating with both alpha- and beta-rhizobia, Mesorhizobium symbionts appeared to exhibit a general host preference for the tribe Psoraleeae, whereas Burkholderia prevailed in the Podalyrieae. Although host genotype was the main factor determining rhizobial diversity, ecological factors such as soil acidity and site elevation were positively correlated with genetic variation within Mesorhizobium and Burkholderia, respectively, indicating an interplay of host and environmental factors on the distribution of Fynbos rhizobia.

Phylogenetic Relationships of Tribe Crotalarieae (Fabaceae) Inferred from DNA Sequences and Morphology

Abstract Tribe Crotalarieae is a large and diverse group of papilionoid legumes that largely occur in Africa. A systematic study of generic relationships within the tribe was undertaken using nucleotide sequences from the internal transcribed spacer (ITS) of nuclear ribosomal DNA, the plastid gene rbcL, and morphological data. The Crotalarieae are supported strongly as monophyletic and sister to the tribe Genisteae. Lebeckia, Lotononis, and Wiborgia are all paraphyletic in the molecular analyses and morphological data support the division of Lebeckia into three more natural genera (one of which includes the monotypic North African Spartidium). Four major lineages were identified within the tribe based on sequence data: the “Cape” group, comprising Aspalathus, Lebeckia, Rafnia, Spartidium, and Wiborgia; the Lotononis group, comprising Lotononis pro parte, Pearsonia, Robynsiophyton, and Rothia; a group comprising Lotononis section Leptis, L. section Listia, and allies; and the Crotalaria group, comprising Bolusia, Crotalaria, and Lotononis hirsuta (Lotononis section Euchlora). Morphological analysis yields a similar topology, except that Lotononis is monophyletic if L. hirsuta were excluded. When the molecular and morphological data sets are combined, the same major clades are retrieved as in the molecular analysis, with the notable exception that Lotononis and Lebeckia senso stricto are supported as monophyletic. The results from this study have important implications for the classification of the tribe Crotalarieae and present an important step towards a natural and phylogenetic generic classification for the tribe.

Hitting the right target: taxonomic challenges for, and of, plant invasions.

Taxonomic resources are essential for the effective management of invasive plants because biosecurity strategies, legislation dealing with invasive species, quarantine, weed surveillance and monitoring all depend on accurate and rapid identification of non-native taxa, and incorrect identifications can impede ecological studies. On the other hand, biological invasions have provided important tests of basic theories about species concepts. Modern taxonomy therefore needs to integrate both classical and new concepts and approaches to improve the accuracy of species identification and further refine taxonomic classification at the level of populations and genotypes in the field and laboratory.

Systematic Position of the Anomalous Genus Cadia and the Phylogeny of the Tribe Podalyrieae (Fabaceae)

Abstract Tribe Podalyrieae is a group of papilionoid legumes that are largely endemic to the Cape Floristic Region of South Africa, possessing fire survival strategies with both nonsprouting and sprouting species. A phylogenetic study of the tribe was undertaken using gene sequences obtained from the internal transcribed spacer (ITS) of nuclear ribosomal DNA as well as the plastid rbcL gene (107 species). Several clades were identified within the tribe. Subtribe Xiphothecinae consists of the genera Amphithalea and Xiphotheca. Subtribe Podalyriinae was paraphyletic. Based on the results of this study, Liparia (except L. calycina) and Podalyria are sister genera with Stirtonanthus sister to both of these. While Podalyria and Stirtonanthus are monophyletic, the monophyly of Liparia is still uncertain. Virgilia and Calpurnia are closely related and Cyclopia retains an isolated, monophyletic position within the tribe. Cadia is monophyletic and sister to the rest of the Podalyrieae. The placement of this genus has, until now, been uncertain due to their actinomorphic flowers that are unusual among papilionoid legumes. The data from this study indicate that actinomorphic flowers may be interpreted as an apomorphy for Cadia and it shares many characters with Podalyrieae. We therefore propose that Cadia be transferred to Podalyrieae from the paraphyletic tribe Sophoreae. The age of the root node of the tribe Podalyrieae s.s. was estimated at 30.5 ± 2.6 million years (Ma) using nonparametric rate smoothing (NPRS) and 34.7 Ma (confidence intervals: 25.1–44.1 Ma), using a Bayesian relaxed clock, indicating that a major radiation has taken place during the middle to late Miocene and early Pliocene. Finally, we found that nonsprouting species have a higher rate of molecular evolution than sprouting species.

A Molecular Phylogeny and Generic Classification of Asphodelaceae subfamily Alooideae: A Final Resolution of the Prickly Issue of Polyphyly in the Alooids?

Abstract Phylogenetic analysis of plastid (rbcLa, matK, trnH-psbA and the trnL intron) and nuclear (ITS1) sequence datasets in a wide sampling of species of Asphodelaceae: Alooideae provides a generally well-resolved phylogeny. Among traditionally accepted genera only Astroloba and Gasteria are supported as monophyletic. Species of Haworthia are distributed among three clades corresponding to the current subgenera. Aloe s. l. (including Chortolirion) segregates into six, well-supported clades corresponding respectively to sections Dracoaloe (= Aloidendron), Kumara + Haemanthifoliae, Macrifoliae, Aristatae, Serrulatae, and the remainder of the genus. The first three clades are retrieved as early branching lineages, whereas A. sects. Aristatae and Serrulatae are strongly supported as members of a clade including Astroloba + Haworthia subg. Robustipedunculatae. We examine possible options for recircumscribing the genera of Alooideae as reciprocally monophyletic entities. Although morphological and molecular data are consistent with expansion of Aloe to include all members of Alooideae, we accept and implement an alternative option maintaining historical usage in the group as far as possible. Astroloba and Gasteria are retained as currently circumscribed; Haworthia is restricted to H. subg. Haworthia; the genus Tulista is accepted for members of H. subg. Robustipedunculatae, with the new combination T. minima; and H. subg. Hexangulares is treated as the genus Haworthiopsis with the new combinations H. koelmaniorum, H. pungens, and H. tessellata. The genus Aloe is restricted to the clade comprising the ‘true aloes’, with Aloidendron, Aloiampelos, and Kumara accepted as segregates, the latter broadened to include A. haemanthifolia as K. haemanthifolia. Aloe aristata is segregated in the monotypic genus Aristaloe as A. aristata and Aloe sect. Serrulatae is treated as the new genus Gonialoe with the species G. dinteri, G. sladeniana, and G. variegata.

A global infrageneric classification system for the genus Crotalaria (Leguminosae) based on molecular and morphological evidence.

Crotalaria is a large genus of 702 species with its centre of diversity in tropical Africa and Madagascar and secondary radiations in other parts of the world. The current infrageneric classification system is based on morphological and morphometric studies of the African taxa only and is here re-evaluated using a phylogenetic approach. DNA sequences derived from the nuclear ITS and the plastid matK, psbA-trnH and rbcLa markers were analyzed using parsimony and model-based (Bayesian) approaches. The resultant molecular phylogeny allowed for a new interpretation of diagnostically important morphological characters, including specialisations of the calyx, keel, standard petal and style, which are variously convergent in several unrelated infrageneric groups. Of particular interest is the congruence between the new phylogeny and the distribution of standard petal callosity types. A sectional classification system for the entire genus is proposed for the first time. The new system that is formalised here comprises eleven sections: Amphitrichae, Calycinae, Crotalaria, Geniculatae, Glaucae, Grandiflorae, Hedriocarpae, Incanae, Schizostigma, Borealigeniculatae and Stipulosae. Sectional limits of the Geniculatae, Calycinae and Crotalaria are modified. The subsections Stipulosae, Glaucae and Incanae are raised to sectional level, while some groups previously recognized as subsections are abandoned due to non-monophyly (subsections Chrysocalycinae, Hedriocarpae, Macrostachyae and Tetralobocalyx). Two new sections are recognized, Amphitrichae and Borealigeniculatae.

A taxonomic revision of the genus Rothia (Crotalarieae, Fabaceae)

Rothia Pers. is a genus of papilionoid legumes that consists of two species, R. indica (L.) Druce and R. hirsuta (Guill. & Perr.) Baker. The genus is a member of the tribe Crotalarieae and is widely distributed in Africa, Asia and Australia. Recent molecular systematic studies have shown the genus to be closely related to Robynsiophyton Wilczek and Pearsonia Dummer; however, it is easily distinguished from these by its 10 small, rounded anthers and subequally lobed calyx (as opposed to the large, elongate anthers of Pearsonia or the 9 stamens of Robynsiophyton). These three genera share characters such as uniform anthers, straight styles and the presence of angelate esters of lupanine-type alkaloids. Leaf and fruit anatomy of Rothia and Robynsiophyton were also studied but revealed no informative differences. Both genera have dorsiventral leaves with mucilage cells in the epidermis and thin-walled fruits. A taxonomic revision of Rothia is presented, including a key to the species, correct nomenclature, descriptions, illustrations and distribution maps.

Taxonomy of Wiborgiella (Crotalarieae, Fabaceae), a Genus Endemic to the Greater Cape Region of South Africa

Abstract A taxonomic revision of the recently described genus Wiborgiella is presented. Nine species are recognized within the genus, two of which are newly described, W. dahlgrenii and W. vlokii . The genus is endemic to the Cape region of South Africa and most species are highly localized and rare. Wiborgiella species can be distinguished from other genera in the tribe Crotalarieae by a combination of brown young branches (early formation of bark in the stems of the perennial species), laminar trifoliolate leaves, glabrous petals, a 4 + 6 anther arrangement, and oblong, wingless, inflated fruit. Anatomical studies revealed that all species of the genus have dorsiventral leaves (mesophyll differentiated into palisade parenchyma adaxially and spongy parenchyma abaxially) with mucilage cells in the epidermis which distinguishes Wiborgiella from other closely related genera, such as Calobota which has isobilateral leaves without mucilage cells. The fruits of Wiborgiella species are all thin-walled, have highly sclerified mesocarps and mucilage cells are present in some species. These fruit character states are also present in other genera of the Crotalarieae. The taxonomic treatment of the genus includes a key to the species, descriptions, illustrations, nomenclature, typification, and geographical distribution of each species.