Alvaro M Viljoen

Phenolic variation in wild populations of Aspalathus linearis (rooibos tea)

Abstract Rooibos tea, a herbal tea derived from Aspalathus linearis (Fabaceae—tribe Crotalarieae) has become increasingly popular as a health drink. The beneficial properties are partly ascribed to the phenolic constituents in the plant, which are enzymatically modified during processing. Within the species, distinct geographical forms can be recognised, differing in habit, fire-survival strategy, vegetative and reproductive morphology, enzyme patterns and flavonoids. Several phenolic compounds are known to occur in A. linearis . The main constituent of the commercial tea type (also known as the Rocklands type or the red tea type) is the dihydrochalcone aspalathin, but the presence of other flavonoids such as nothofagin, orientin, isoorientin, vitexin, rutin and isoquercetrin has been reported. These compounds are found in the processed product, as well as the dried leaves. The relative quantities of phenolic compounds show large qualitative and quantitative differences between populations and provenances of the wild tea types. Within populations, however, the patterns are remarkably uniform. Aspalathin was found to be the main compound in processed (“fermented”) tea and also in dried leaves of several tea types. The compound is absent in some wild tea populations, where other flavonoids occur as the main phenolics, notably orientin, isoorientin and rutin. Rutin is invariably the main compound in Aspalathus pendula , a close relative of A. linearis that is rarely used to make tea. An overview of natural variation in phenolic compounds of the main wild tea types is presented.

Distribution and chemotaxonomic significance of flavonoids inAloe (Asphodelaceae)

A chemotaxonomic study of practically all the species of the genusAloe showed that flavonoids occur as major compounds in 31 out of a total of 380 species investigated. Flavanones and dihydroflavonols are present in the exudate of species inAloe ser.Rhodacanthae andSuperpositae and also in a number of the endemic species from Madagascar. Flavones occur as the only major compound in the leaf extracts of the sects.Leptoaloe andGraminialoe. In ser.Macrifoliae and inLomatophyllum, the sister genus ofAloe, isovitexin co-occurred with theC-glucosylanthrone aloin. The chemotaxonomic implication of these results are discussed together with the significance of the taxonomic and chemogeographical distribution of flavonoids inAloe. With a few rare exceptions, the leaf compounds from two different biogenetic pathways (polyketide pathway and flavonoid pathway) are mutually exclusive. Since flavonoids are restricted to the basal groups inAloe, we conclude that flavonoids are plesiomorphic characters inAloe reflecting ancient phylogenetic and biogeographic links.

The occurrence and taxonomic distribution of the anthrones aloin, aloinoside and microdontin in Aloe

A chemotaxonomic survey of 380 species of Aloe indicated the presence of the anthrone isomers aloin A and B together with the aloinoside isomers and microdontin A and B in 36 (10%) species of Aloe. This group, referred to as the microdontin chemotype, is thus characterised by a combination of exudate compounds and not merely a single phytochemical marker, implying taxonomic significance of leaf exudate compounds. The 36 representatives of the group occupy disparate taxonomic positions in the largely artificial hierarchy of the present classification system. Although many of the species have previously been considered as related (based on macromorphology only), a large number of species have not been associated with one another before. The chemical profiles and leaf exudate compositions of the species are presented, followed by a brief summary of the morphological diversity. Whilst conceding the possibility of convergent evolution, the geographical distribution of the species and thoughts on possible relationships between the taxa are discussed.

The chemotaxonomic significance of the phenyl pyrone aloenin in the genus Aloe

The phenyl pyrone, aloenin was positively identified in 16 species in a greater chemotaxonomic study on 380 species of Aloe. A large number of species have previously been suggested to be related on the basis of their macromorphological characters. The leaf exudate composition of the 16 species are presented together with a summary of the salient morphological characters. The possible taxonomic relationships between aloenin producing species, not previously thought to be associated with one another are discussed and illustrates the need to explore additional characters of taxonomic value in this large genus of ca. 420 species where no natural classification system exists.

Plicataloside in Aloe - a chemotaxonomic appraisal

In a chemotaxonomic survey of 380 taxa of Aloe, 20 species were found to contain the naphthalene derivative plicataloside as the major phenolic in the leaf exudate. Most of these species are restricted to East Africa (Kenya, Uganda and Tanzania). Only three species (A. chabaudii, A. palmiformis, A. plicatilis) in southern Africa contained this compound while the Malagasy endemics studied were found to be devoid of plicataloside. Macromorphology of the species was examined to search for other characters common to the species, and taxonomic affinities are assessed. Previous studies have suggested some of the taxa defined by this unique chemical compound to be taxonomically related, while many of the taxa have not previously been associated together.

Aloeresins E and F, two chromone derivatives from Aloe peglerae

Abstract The structures of two new aloesin derivatives isolated from Aloe peglerae, viz. , 2- acetonyl -8-(2-O- cinnamoyl -β- d -glucopyranosyl) -7-β- d -glucopyranosyloxy-5-methylchromone (aloeresin E) and 2- acetonyl -8-(2-O- cinnamoyl -β- d -glucopyranosyl)-7-methylchromone (aloeresin F) were determined by spectroscopic methods.

Anthrones from Aloe microstigma

5-Hydroxyaloin A and a new anthrone, named as microstigmin A, were isolated from the leaf exudate of Aloe microstigma. The structure of microstigmin A was determined by spectroscopic techniques as well as by conversion into 5-hydroxyaloin A.

A chemotaxonomic and morphological appraisal of Aloe series Purpurascentes, Aloe section Anguialoe and their hybrid, Aloe broomii.

Evidence is presented to suggest the hybrid origin of Aloe broomii, with the one putative parent belonging to Aloe series Purpurascentes and the other a member of Aloe series Anguialoe. A chemotaxonomic and morphological assessment is presented for both infrageneric groups and their hypothesised hybrid. Four of the species belonging to the series Purpurascentes display a characteristic leaf exudate profile containing the chemotaxonomic marker microstigmin. Aloe gariepensis and A. succotrina lack the diagnostic leaf exudate compounds. The distinct morphological apomorphies for Aloe section Anguialoe are supported on the chemical level reinforcing the monophyly of this group.

The chemotaxonomic value of the diglucoside anthrone homonataloside B in the genus Aloe

Abstract The chemotaxonomic value of the only known diglucoside anthrone from Aloe , homonataloside B, is discussed. This compound has been detected in only 14 species in a chemotaxonomic survey of 380 Aloe species. The homonataloside B-accumulating species are only found in Africa with none of the Malagasy endemics producing this compound. A summary of the morphological variation is presented together with the taxonomic distribution of this unique anthrone. The representatives of this distinct chemotype occupy disparate positions in the largely artificial hierarchy of the present classification system. Species included in this chemotype provide chemical evidence of hybridisation in Aloe .