The southern African species of Leonotis (Pers.) R. Br. are revised. Nine taxa
are recognised including a new species and two new subspecies.
A multidisciplinary approach was adopted involving: floral, vegetative,
seedling and fruit morphology, karyology, palynology, pollination biology,
phytogeography, phytochemistry and cladistics. Of these characters the most
important in delimiting species is leaf morphology.
Phytochemistry revealed qualitative and quantitative differences in essential
oils between taxa. Germacrene is the dominant essential oil in seven species,
particularly in L. dubia E. Mey. and L. nepetifolia (L.) R. Br. Caryophyllene
dominates in L. randii S. Moore. Although certain species have characteristic
aromas, no inter-specific differences are apparent in the levels of α-copaene,
the dominant volatile essential oil extracted with Tenax. Essential oil data is in
partial agreement with the phylogeny and species concepts presented in this
document.
Omithophily accounts for most fruit set in perennial species but in the annual
species (L. nepetifolia) autogamy prevails. Neither omithophily nor
entomophily improved nutlet vigour which was gauged from nutlet
germination. Leonotis species are predominantly pollinated by a variety of
sunbirds, although bees are also involved. Nectar is sucrose-dominant in
perennial species but hexose-dominant in the annual.
The majority of species are concentrated along the eastern seaboard with the
eastern Cape forming the centre of diversity. The widespread distribution and
tropical affinities of L. leonurus (L.) R. Br., suggest an origin for the genus in
tropical Africa. Migration to southern Africa and subsequent speciation are
suggested. Habitat diversity and edaphic conditions probably played an
important role in the evolution of narrowly distributed xerophytic species. A cladistic analysis re-emphasised that Leonotis is a monophyletic group of
closely related species. The lack of floral divergence in perennial species
indicates the constraints imposed by ornithophily. The annual, L. nepetifolia, is
highly derived and displays numerous autapomorphies. The morphology,
distribution and tropical affinities of L. leonurus are interpreted as
pleisiomorphic. The proposed phylogeny is reasonably compatible with
phytogeographic data. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1995.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/10332 |
| Date | January 1995 |
| Creators | Vos, Wayne Thomas. |
| Contributors | Edwards, Trevor J., Van Staden, Johannes., Smith, Michael Trevor. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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