Abraham E. van Wyk

Documented Utility and Biocultural Value of Aloe L. (Asphodelaceae): A Review

Documented Utility and Biocultural Value ofAloeL. (Asphodelaceae): A Review. The genus Aloe L. (Asphodelaceae) comprises 548 accepted species, of which at least one-third are documented as having some utilitarian value. The group is of conservation concern due to habitat loss and being extensively collected from the wild for horticulture and natural products. Cultural value is increasingly important in the effective conservation of biodiversity. The present study evaluated the biocultural value of the known uses of Aloe, excluding the domesticated and commercially cultivated A. vera. Over 1,400 use records representing 173 species were collated from the literature and through personal observation; this paper presents a synopsis of uses in each of 11 use categories. Medicinal uses of Aloe were described by 74% of the use records, followed by social and environmental uses (both 5%). Species yielding natural products, notably A. ferox and A. perryi, were most frequently cited in the literature. Consensus ratios indicate that the most valued uses of Aloe are in medicine and pest control against arthropods and other invertebrates.

Pollen morphology of Adenandra (Rutaceae: Diosminae) and its taxonomic implications

The pollen morphology of Adenandra Willd. (Rutaceae: Diosminae) was investigated to determine its taxonomic significance. Pollen of 27 of the 30 infrageneric taxa (representing 16 of the 18 species) was investigated by LM, SEM and TEM. Adenandra differs from all other Diosminae in having 4-colporate rather than 3-colporate pollen grains. This supports the alleged monophyletic status of the genus. Exine morphology and structure, however, is extremely diverse considering the size of the genus, with eight distinct pollen types and four subtypes being discerned. In some members the grains have uniform macroreticulate, striate or striato-reticulate sculpturing, whereas in others the poles have striate, striato-reticulate or reticulate-perforate sculpturing with various types of reticulate or rugulate sculpturing at the mesocolpia. Taxonomic groupings revealed by the pollen characters suggest elationships between taxa that were not previously apparent. It is suggested that evolutionary diversification among spe...

Evolutionary history and leaf succulence as explanations for medicinal use in aloes and the global popularity of Aloe vera

BackgroundAloe vera supports a substantial global trade yet its wild origins, and explanations for its popularity over 500 related Aloe species in one of the world’s largest succulent groups, have remained uncertain. We developed an explicit phylogenetic framework to explore links between the rich traditions of medicinal use and leaf succulence in aloes.ResultsThe phylogenetic hypothesis clarifies the origins of Aloe vera to the Arabian Peninsula at the northernmost limits of the range for aloes. The genus Aloe originated in southern Africa ~16 million years ago and underwent two major radiations driven by different speciation processes, giving rise to the extraordinary diversity known today. Large, succulent leaves typical of medicinal aloes arose during the most recent diversification ~10 million years ago and are strongly correlated to the phylogeny and to the likelihood of a species being used for medicine. A significant, albeit weak, phylogenetic signal is evident in the medicinal uses of aloes, suggesting that the properties for which they are valued do not occur randomly across the branches of the phylogenetic tree.ConclusionsPhylogenetic investigation of plant use and leaf succulence among aloes has yielded new explanations for the extraordinary market dominance of Aloe vera. The industry preference for Aloe vera appears to be due to its proximity to important historic trade routes, and early introduction to trade and cultivation. Well-developed succulent leaf mesophyll tissue, an adaptive feature that likely contributed to the ecological success of the genus Aloe, is the main predictor for medicinal use among Aloe species, whereas evolutionary loss of succulence tends to be associated with losses of medicinal use. Phylogenetic analyses of plant use offer potential to understand patterns in the value of global plant diversity.

Conserving Acacia Mill. with a conserved type. What happened in Vienna

This note documents the events and conduct that led to the acceptance of Report 55 of the Permanent Committee for Spermatophyta concerning the conservation of Acacia Mill. with a new type. The procedures followed by the Nomenclature Section of the XVII th International Botanical Congress (IBC) held in Vienna, Austria, in July 2005, are also outlined and briefly described in accordance with the provisions of the International Code of Botanical Nomenclature (ICBN) for dealing with committee reports. This controversial proposal to retypify Acacia Mill. from an African to an Australian type was accepted by the Committee for Spermatophyta, the General Committee, and the Nomenclature Section, a recommendation ratified by the final closing plenary session of the IBC. The ICBN emanating from the XVII th IBC will include Acacia Mill., with a conserved type, in Appendix IIIA Nomina generica conservanda et rejicienda. For those who choose to follow the traditional classification system that applies the name Acacia in a broad sense to a heterogeneous assemblage of species comprising a number of subgenera, this decision holds no implications at generic level. However, should the alternative classification which segregates a broadly defined Acacia into a number of genera be followed, then the name Acacia would apply in a strict sense to the mainly Australian wattles (previously Acacia subg. Phyllodineae-now A. subg. Acacia-of the traditional system.).

Pollen morphology of Canthium, Keetia and Psydrax (Rubiaceae: Vanguerieae) in southern Africa

Pollen of all the southern African members of Canthium, Keetia and Psydrax was studied by means of LM, SEM and TEM. Palynologically these three genera can easily be distinguished from one another, exine structure and sculpturing being the most useful characters. The sexine is essentially perforate with short columellae not usually distinguishable in SEM in the Canthium type, coarsely reticulate with long columellae in the Keetia type and more finely reticulate with short columellae in the Psydrax type. Palynologically Canthium sensu stricto (used here to refer to the Canthium complex excluding Psydrax, Keetia and Pyrostria) is clearly distinct from Keetia and Psydrax, but similar to the other members of the Vanguerieae. This supports the proposed subdivision of Canthium sensu lato in southern Africa into these three genera. Differences amongst the various Canthium sensu stricto species suggest at least three different pollen sub‐types. Bridsons placement of C. inerme and C. suberosum in the subgenus Lyci...

Bark Structure and Intergeneric Relationships of Some Southern African Cassinoideae (Celastraceae)

At present Cassine in southern Africa is treated in a wide sense (s.l.), including amongst others Allocassine p. p., Cassines. str., Crocoxylon, Elaeodendron, Lauridia, and Mystroxylon. A comparative anatomical study was made of mature bark representing 16 southern African species of Cassine s.l., and the monotypic Allocassine, Hartogiella and Maurocenia (all members of the subfamily Cassinoideae). Six bark types are distinguished on the basis of the type of sclerenchymatous elements in the secondary phloem; presence or absence of styloid crystals, e1astic threads, and sclerified phelloderm; stratified homogeneous phellem; and degree of rhytidome development. These correlate to a considerable extent with the generic subdivision of Cassine s.l. proposed by Loesener (1942) and Robson (1965). On the basis of bark anatomy and other evidence, it is proposed that the circumscription of Cassine be restricted to include only the southern African species C. peragua and C. parvifolia, and possibly Hartogiella. Crocoxylon, Elaeodendron, Lauridia and Mystroxylon should be reinstated or maintained, although with some modification of the originally defined generic limits.

Palynology of the Genus Passerina (Thymelaeaceae): Relationships Form and Function

Abstract Pollen of the genus Passerina L. differs markedly from that of other southern African members of the Thymelaeaceae. Grains of most members of the Thymelaeaceae are characterised by a typical croton pattern, comprising rings of more or less trihedral sexine units mounted on an underlying reticulum of circular muri. In Passerina, however, the supratectal subunits are fused completely to form a continuous reticulum, which replaces the underlying reticulum. The reticulum in Passerina is therefore secondary in origin and not homologous with the basal reticulum of typical crotonoid grains in the family. The croton pattern has often been used as indication of a possible relationship between the Euphorbiaceae and Thymelaeaceae. Pollen of Passerina is adapted to anemophily. Grain sculpturing clearly demonstrates secondary derivation of a reticulate pattern from the typical croton pattern, through reduction, aggregation and fusion. Pollen of Passerina represents a climax of a continuum of variation in the ...

Wood Structure and Generic Status of Some Southern African Cassinoideae (Celastraceae)

Opinions differ on whether to treat Cassine in southern Africa in a wide sense, or to recognise several segregate genera, such as Elaeodendron, Crocoxylon, Lauridia, Mystroxylon and Cassine s. str. A comparative anatomical study was made of mature wood representing 17 southern African species of Cassine s.l., Pleurostylia and the three monotypic genera, Allocassine, Hartogiella and Maurocenia (all members of the subfamily Cassinoideae). The wood structure is described with emphasis on the taxonomic value of quantitative and qualitative characters. Various features were found to be diagnostic at supraspecific level. The presence or absence of scalariform perforation plates, septate fibres, various ray types, and additional quantitative characters could be useful for taxonomic application, especially for generic delimitation. Three principal wood types, of which one encompasses three subtypes, are recognised among the species examined. Wood anatomical evidence tells against a wide generic concept for Cassine, and favours the recognition of segregate genera.

Palynology of southern African Boraginaceae: The genera Lobostemon, Echiostachys and Echium

The tribe Echieae of the subfamily Boragineae (Boraginaceae) is represented in southern Africa by the genera Lobostemon Lehm, and Echiostachys Levyns, endemic to the south‐western Cape region, and two species of Echium L., E. plantagineum L. and E. vulgare L., both introduced weeds of cultivation. Pollen of all these genera was studied and only one pollen type is recognized. Grains are tricolporate, heteropolar and triangular in equatorial view; ora more or less circular and situated towards the broader pole; tectum reticulate with densely spaced lumina; suprateetal nodules are situated at margins of lumina. The P/E ratio varies from 1.08 to 1.63. Genera of the Echieae are sometimes placed in the tribe Lithospermeae. A comparison of the pollen of the studied genera with that of Lithospermum, confirms that the tribe Echieae should be retained. Pollen of Lithospermum is 6–8‐zonocolporate, usually more or less isopolar and with colpi rhombic in outline. The presence of zygomorphic flowers and absence of calc...

Bark Structure and Preferential Bark Utilisation by the African Elephant

Bark fracture properties are thought to influence the debarking of selected trees by the African elephant. This hypo thesis was tested for large riverine tree species in the Northern Tuli Game Reserve, Botswana. An index of bark breakage strength and pliability of secondary phloem tissue was compiled for 11 common riverine species, and the bark anatomy of these species was investigated to determine relative fibrosity. The majority of species preferred by elephants have strong and pliable barks, associated with a high proportion of fibres. However, not all preferred species have these characteristics, which indicates that factors other than bark fracture properties affect species preference. Bark structure influences the way pieces of bark are stripped from a tree trunk during debarking. It is hoped that this paper will stimulate further studies on the effects of bark structure on the preferential feeding behaviour of the African elephant.