Systematics of Crabbea Harv. (Acanthaceae) in southern Africa
De Gouveia, Nelson Alexander Mendes
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The purpose of this study is to provide an updated taxonomic revision and a molecular phylogenetic investigation of Crabbea Harv. (Acanthaceae) in southern Africa. The taxonomic component of this study entailed a detailed analysis of anatomical, macromorphological and micromorphological data and appropriate descriptions. Updated distribution maps of each southern African Crabbea species is presented and detailed habitat and ecological information is also provided. Four different identification keys were constructed using leaf anatomy, leaf micromorphology, pollen micromorphology and macromorphology. Type literature, type material and nomenclature for each investigated Crabbea species is critically reviewed. In cases where holotype material could not be located and/or identified, appropriate isotypes, lectotypes, syntypes and/or neotypes were assigned and/or confirmed. Additional herbarium specimens, on loan and electronic scans, from various European and South African herbaria were studied to construct identification keys, species descriptions, distribution maps and obtain ecological and habitat information. Fresh material was collected for each investigated species. The investigated Crabbea species are all small to medium-sized herbs with cymose inflorescences and corolla being two-lipped, zygomorphic, funnel-shaped with paired, raised bosses. The corolla tube is largely creamish-white but light pink corolla tubes are occasionally found. Growth form, root appearance, stem orientation, position, texture and leaf shape and indumentum are important for species-level identification. Leaf micromorphological characters are both significant on species level. The occurrence of both amphistomatic and hypostomatic leaves among the investigated species are characteristic of Acanthaceae and could be effectively used to distinguish the investigated Crabbea species from each other. This study provides a first detailed analysis of Crabbea cystoliths. Cystolith attachment width on the adaxial leaf surface proves to be the best character state to split the southern African Crabbea into two groups. The groupings obtained were similar to that of the leaf micromorphology groupings. Pollen micromorphology divided Crabbea into two groups based on the absence or presence of murus and lumin. However, this character set yielded a different grouping from the leaf micromorphology and anatomy character sets. Pollen grain morphology for certain Crabbea species either remained constant over a geographic range, or varied between and within populations. Macromorphology could key-out all species, except C. cirsioides and C. nana. This character set displays a similar grouping to that of the pollen micromorphology character set. The molecular phylogenetic component of this study resulted in the first molecular investigation of the phylogeny for the southern African Crabbea species. The phylogeny is primarily based on the two chloroplast DNA sequences trnL-trnF and rps16; however, anatomical and morphological characters are also included in the phylogeny to increase the resolution of the tree in absence of the ITS sequences. Molecular phylogenetic results suggest that C. velutina is the first diverging southern African Crabbea species, from the larger Crabbea clade, consisting of C. acaulis, C. angustifolia, C. cirsioides, C. galpinii, C. ovalifolia and C. pedunculata. Within the larger Crabbea clade, C. acaulis forms a distinct clade as well as C. galpinii and C. pedunculata. The molecular results confirm the close relationship between C. galpinii and C. pedunculata. Moreover, within the larger Crabbea clade, molecular data could not clearly resolve and group the sprawling Crabbea species into distinct clades, as in the case of C. angustifolia, C. cirsioides and C. ovalifolia. The end result of this systematic study provides a new insight into the classification of the southern African Crabbea species and the genus Crabbea. Crabbea galpinii and C. pedunculata are confirmed as two separate, sister species and C. nana is now regarded as a synonym of C. cirsioides. Seven Crabbea species are recognised in southern Africa.