Trevor J. Edwards

Effect of burning and mowing on grass and forb diversity in a long-term grassland experiment

Abstract Disturbance may be an important determinant of plant community composition and diversity owing to its effects on competitive interactions, resources, dominance and vigour. The effect of type, timing and frequency of disturbance on grass and forb species richness was examined using data from a long-term (> 50 yr) grassland burning and mowing experiment in KwaZulu-Natal, South Africa. Grass species richness declined considerably (> 50%) in the absence of disturbance, whereas forb species richness was unaffected. Annual burning in sites not mown in summer tended to increase grass species richness relative to triennial burning (22% increase) with the reverse being true in sites mown twice in summer (37% decline). Forb species richness declined by 25% in sites mown twice in summer relative to sites mown in early summer only. Disturbance was necessary to achieve maximum grass species richness presumably by removing litter and increasing the availability of light. The interaction of time of mowing in summer (early versus late) and time of burning during the dormant period (spring versus winter) had the most dramatic effect on species richness. Time of burning had no effect on richness in sites mown in early summer, but winter burning resulted in a dramatic decline (27–42%) in richness in sites mown in late summer. This effect may be related to possible greater soil desiccation with this combination of disturbances. Nomenclature: Arnold & De Wet (1993). Abbreviation: AGP = Above-ground phytomass production.

Refugia, dispersal and divergence in a forest archipelago: a study of Streptocarpus in eastern South Africa

We describe a scenario of plant speciation across a relict forest archipelago in South Africa involving Pleistocene habitat expansion‐contraction cycles, dispersal and adaptation to lower temperatures. This is the first population level study using molecular data in South African forests and has significant implications for conservation efforts in this area. Populations of the mesophytic forest floor herbs Streptocarpus primulifolius sensu lato and Streptocarpus rexii were sampled throughout their range in the naturally fragmented forests of eastern South Africa in order to investigate population genetic and phylogenetic patterns within the species complex, using nuclear microsatellites, nuclear ribosomal ITS (internal transcribed spacer) sequences and chloroplast genome sequences. S. primulifolius harbours high levels of genetic diversity at both the nuclear (mean HE = 0.50) and the chloroplast level (each population fixed for a unique haplotype). This is consistent with populations of these coastal species being Pleistocene relicts. In contrast, populations of S. rexii in cooler habitats at higher altitudes and lower latitudes harbour little or no nuclear genetic diversity (mean HE = 0.09) and most share a common chloroplast haplotype. The split of S. rexii from populations intermediate between the two species (S. cf. primulifolius) occurred between 0 and 0.44 million years ago according to the calibrated ITS phylogeny of the taxa. The low genetic diversity and homogeneity of S. rexii is congruent with this species having reached its current range during the Holocene. We found no evidence of monophyly of any of the taxa in this study, which we consider a consequence of recent evolution in a fragmented habitat.

Figs of Southern and South-Central Africa

‘Figs of Southern and South-Central Africa’ is anachronistic! The modern world, with its hectic lifestyle and overambitious goals, propagates reams of beautiful, rehashed texts. The Achilles heel of descriptive sciences, such as plant taxonomy, is that they accumulate inaccurate baggage which is perpetuated by this mindless rehashing of information. How refreshing to encounter a book which has been meticulously researched from its foundations. Such an approach is costly in effort, finance and time; however, the product speaks for itself. The authors have unravelled nomenclatural puzzles, come to terms with species boundaries, geographic and environmental variation and produced convincing species accounts, an achievement which escapes many similar popular books. While uncompromising in its scientific accuracy, the book is sympathetic to the layperson (and many a scientist averse to using botanical keys) in being liberally illustrated. The colour photography has been contributed from various sources and documents habitat, habit and morphology of flowering and fruiting material. The family is without doubt photogenic but it takes talent to capture the artistic images which liberally adorn the text. Line drawings are too seldom used in modern literature because, when executed with skill, they are peerless in conveying information. The pen-and-ink drawings complement the photographic record superbly. Figs have great horticultural appeal and the book provides useful information for nurseries and indigenous gardeners in the chapters entitled ‘Figs, birds and other wildlife’ by Duncan Butchart, and ‘Growing figs’ by Geoff Nicholas. Simon van Noort outlines the obligate mutualisms that exist between figs and fig wasps in a fascinating chapter. Scanning electron micrographs illustrate the micromorphological evolution of wasp body parts and colour photographs depict the remarkable ovipositors of parasitoid wasps. A comprehensive geographic table is provided, outlining figs and their associated wasp fauna. In all, the book covers 88 species, 48 indigenous and 17 exotic fig species. The remaining species are allied genera of the Moraceae, including mulberries (Morus), breadfruit (Artocarpus) and the delightful herbs of Dorstenia. It is an excellent buy for the professional botanist and layperson alike.

The impact of pollination syndrome and habitat on gene flow: a comparative study of two Streptocarpus (Gesneriaceae) species

Gene flow through pollen and seed dispersal is important in terms of population differentiation and eventually speciation. Seed and pollen flow are affected in turn by habitats and pollen vectors. We examined the effect of different pollinators and habitats on gene flow by comparing two species of Streptocarpus, using microsatellite and chloroplast RFLP markers. Populations of the forest-dwelling S. primulifolius were highly differentiated according to nuclear microsatellite data and had mutually exclusive chloroplast haplotypes. This result is congruent with infrequent seed dispersal and limited between-population foraging by the long-tongued fly pollinator Stenobasipteron wiedemanni. In contrast, populations of S. dunnii growing in exposed crags had lower levels of population differentiation according to both nuclear and chloroplast data, congruent with a hypothesis of more effective between population seed dispersal and greater pollen-mediated gene flow due to the sunbird pollinator Nectarinia famosa. The population genetic behavior of these species is reflected in their taxonomy and phylogenetic position; S. primulifolius belongs to a taxonomically complex clade in which recent speciation is evident, while the clade containing S. dunnii is characterized by taxonomically well-defined species on longer phylogenetic branches. Our study shows that pollinator movements and seed dispersal patterns are a major determinant of the evolutionary trajectories of these species.

Phylogeny of Bonatea (Orchidaceae: Habenariinae) based on molecular and morphological data

The genus Bonatea is widely distributed throughout southern and eastern Africa. Considerable debate surrounds the generic status of Bonatea, but there have been neither previous studies of evolutionary relationships among Bonatea species, nor any tests of the monophyly of the genus in relation to its close relative Habenaria. We investigated phylogenetic relationships between Bonatea and selected Habenaria species using morphology, as well as sequences of the chloroplast gene matK and the internal transcribed spacer (ITS) regions of nuclear ribosomal DNA. A fully resolved cladogram was obtained using morphological data, but neither the ITS, matK, nor combined data sets yielded well-resolved and well-supported phylogenetic structure for Bonatea. There is poor congruence between ITS and matK data for interspecific relationships in Bonatea, whilst the morphological results are largely congruent with the ITS analysis. Relative to Habenaria, there is little sequence variation between Bonatea species, which could indicate a recent and rapid radiation of Bonatea. Although the sampled Bonatea species form a distinct clade, more extensive sampling of Habenaria would be required to establish unambiguously whether or not Bonatea is monophyletic.

Breeding system of a plesiomorphic floral type: an investigation of small flowered Streptocarpus (Gesneriaceae) species

Six different floral morphologies can be found among the ca. 146 species of Streptocarpus occurring in Africa and Madagascar. One of these, a simple, small pouch type, was found to be plesiomorphic for the genus after mapping these floral types onto a molecular phylogeny. The breeding systems and population structure of three species possessing the plesiomorphic small floral morphology, S. micranthus, S. ibityensis and S. lanatus, have been investigated using nuclear microsatellite markers. Significant deviations from panmixia were found both at the between and within population level (S. micranthus θ = 0.708, f = 0.786; S. ibityensis, θ = 0.173, f = 0.138; S. lanatus, θ=0.539, f = 0.646). As a florally diverse genus, Streptocarpus is unusual in having a predominantly selfing, mixed mating breeding system as a plesiomorphic condition.

A synopsis of Argyrolobium (tribe Genisteae, Papilionoideae) in South Africa

A synopsis and key to South African species of Argyrolobium Eckl. & Zeyh. are presented. South Africa constitutes the centre of diversity for the genus and 47 species are recognised. Full synonymy and typification of the South African species are provided, with diagnostic characters, distribution maps and illustrations.

Drimia flagellaris (Hyacinthaceae): a new discovery from KwaZulu-Natal

A new species, D. flagellaris, is described and illustrated. This species appears to be closely allied to D. calcarata and shares semiepigeal bulbs and evergreen, terete leaves distinguished by their much larger size. No intermediates occur between D. flagellaris and sympatric individuals of D. calcarata. The new species is endemic to the Krantzkloof Gorge system of KwaZulu-Natal.