The morphology, anatomy and pollination biology of Mystacidium Lindl., a small,
epiphytic genus of orchids, was investigated within a phylogenetic context.
Morphological and anatomical studies were carried out in order to obtain characters for a
cladistic analysis of the genus using Cyrtorchis arcuata (Lindl.) Schltr. as an outgroup.
The phylogenetic analysis indicated that the genus may not be monophyletic. Two
species of the closely related genus Diaphananthe Schltr., D. caffra (H.Bol.) Linder and
D. millarii (H.Bol.) Linder, appear to be nested within Mystacidium. Mystacidium species
grow in habitats varying from mistbelt forest to dry savanna. Analysis of stable isotope
composition (Ȣ¹³C values) of leaves and roots showed that all Mystacidium species, as
well as D. caffra and the outgroup C. arcuata, employ CAM photosynthesis. The Ȣ¹³C
values were significantly negatively correlated with mean annual rainfall at the collection
sites. Breeding system experiments revealed that Mystacidium is dependent on
pollinators for fruit set, and that self-pollination results in substantially reduced seed set
due to either inbreeding depression or partial self-incompatibility. Field observations
revealed that M. venosum Harv. ex Rolfe and M. capense (L.f.) Schltr. are hawkmoth-pollinated,
and that M. gracile Harv. and M. pusillum Harv. are pollinated by settling
moths. The spurs of the flowers contain dilute, sucrose-dominant nectar. Mystacidium
venosum and M. capense showed evidence of nectar reabsorption. Nocturnal emission of
scent occurred in all species except M. aliceae H. Bolus and M. brayboniae Summerh.,
which are unscented, and was composed largely of a combination of monoterpenes and
benzoids. Despite substantial variation in spur length (1 - 4.7 cm) among species, no
evidence for directional selection on spur length was found in M. venosum, M. capense or
M. gracile. Hand pollinations significantly increased fruit set in M. capense in two
consecutive seasons at different sites, indicating pollen limitation. Although pollen
removal was greater than pollen receipt in M. venosum, M. capense and M. gracile,
suggesting transport loss or insufficient visitation, a remarkably high percentage of removed pqllen reached stigmas (35 - 50%). Experiments on M. venosum revealed that
flower longevity is reduced by pollination, and that pollinia removed from flowers
remained viable for up to 20 days under field conditions. The phylogeny indicated that
long-spurred, hawkmoth-pollinated species are basal within the genus, and that shorter-spurred species pollinated by noctuid moths are derived. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2002.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/10209 |
| Date | 11 December 2013 |
| Creators | Luyt, Robyn P. |
| Contributors | Johnson, Steven D. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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