Ph.D. / This chemotaxonomic study of the leaf phenolic compounds in the genus Aloe is introduced by presenting a review of Aloe taxonomy, followed by a second review of all known leaf compounds. A chemotaxonomic study of virtually all species of Aloe has made it possible to define several chemical groups in the genus of 420 species. The chemical groups are either identified by a single marker compound or by a series of unique compounds. The following groups have been identified and the chemotaxonomic value of each group is discussed: • An aloin / aloinoside / microdontin group, comprising 36 species, mostly of tropical origin. This group includes species not previously associated with one another. • An 8-O-methyl-7-hydroxyaloin group. Here the co-occurrence of some leaf compounds suggests that 8-O-methyl-7-hydroxyaloin is not homologous in the 18 species where it has been detected. Evidence is presented illustrating that 8-O-methyl-7-hydroxyaloin is an 'hybrid compound' which forms when two chemically divergent species (aloin- and homonataloincontaining parents) are crossed. • An aloenin group, comprising 16 species which are believed to be a monophyletic group. • A microstigmin group, indicating a taxonomic alliance between series Purpurascentes and series Anguialoe, with A. broomii an intermediate between the two. • A 10-hydroxyaloin B group, represented by series Asperifoliae and related species, which appears to be a drought adapted Glade of tropical origin. • A homonataloside group, comprising 14 species, suggesting a biochemical link between the aloes of north Africa and southern Africa. • An aloeresin E and F group, indicating a taxonomic alignment between series Mitriformes and five anomalous species. • A plicataloside group, with its single marker compound indicating a taxonomic relationship between 20 mostly tropical east African species. • A flavone group. The large number of species with flavones (sections Leptoaloe Graminialoe, Lomatophyllum and series Macrifoliae) are suggested to be basal in the genus. • A flavanone group. A few anomalous species produce flavanones but it is unlikely that they form a monophyletic group. A concluding review of leaf exudate compounds (not mentioned above) is also presented which includes hypotheses on the chemotaxonomic value of chromones and anthrones in general. A chemical re-arrangement of species is presented in the form of a new 'chemical classification' for Aloe based on chemotypes. These chemical groups have lead to an improved understanding of natural relationships in a genus where no satisfactory infrageneric classification has hitherto been available.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:3199 |
| Date | 27 August 2012 |
| Creators | Viljoen, Alvaro |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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