Disa draconis

Abstract: Field studies in South Africa showed that floral spur length in the Disa draconis complex (Orchidaceae) varies enormously between populations in the southern mountains (means = 32-38 mm), lowland sandplain (mean = 48 mm), and northern mountains (means = 57-72 mm) We tested the hypothesis that divergence in spur length has resulted from selection exerted through pollinator proboscis length Short-spurred plants in several southern mountain populations, as well as long-spurred plants in one northern mountain population, were pollinated by a horsefly, Philoliche rostrata (Tabanidae), with a proboscis length that varied from 22 to 35 mm among sites Long-spurred plants on the sandplain were pollinated by the tanglewing fly, Moegistorynchus longirostris (Nemestrinidae), which has a very long proboscis (mean = 57 mm) Selection apparently favors long spurs in sandplain plants, as artificial shortening of spurs resulted in a significant decline in pollen receipt and fruit set, although pollinaria removal was not significantly affected Fruit set in the study populations was limited by pollen availability, which further suggests that selection on spur length occurs mainly through the female component of reproductive success

Abstract: The systematic status of Disa draconis (L.f.) Sw. is revised following extensive field studies of population variation in the Western Cape, South Africa. Principal component and cluster analyses revealed clear distinctions between populations from sandplain, semi-arid and montane environments. Diagnostic characters were found in each of the population clusters indicating the existence of a species complex, rather than a single taxon as in the current taxonomy. We propose, therefore, that the name D. draconis (L.f.) Sw. be restricted to the individuals of the sandplain populations from which the type was collected. We reinstate an earlier name, Disa harveiana Lindl., to describe the montane populations which possess several autapomorphic characters. We also show that the geographical variation in spur length and flowering time within this species can be partitioned into two geographically distinct subspecies: D. harveiana subsp. harveiana and D. harveiana subsp. longicalcarata Johnson & Linder. The populations from the semi-arid Karoo region were recognized as a distinct new species, Disa karooica Johnson & Linder, on the basis of their peculiar petal structure. A cladistic analysis indicated that the three species forming the D. draconis complex form a monophyletic and relatively specialized lineage within Disa sect. Coryphaea. The revised classification also has important conservation implications as D. draconis, previously considered a common species, is now restricted to a few highly threatened populations on the west coast near Cape Town.

Abstract: Long-proboscid flies have been documented as the primary pollinators in several long-tubed floral guilds in southern Africa. These specialized pollination systems have become models for studying floral mimicry, adaptation, and coevolution. In this study we document a previously unknown pollinator of Pelargonium stipulaceum (L.f.) Willd. (Geraniaceae) and Disa karooica Johnson & Linder, a species within the Disa draconis complex (Orchidaceae), and propose the occurrence of a new floral model-mimic system in the semiarid interior of South Africa. We find that Philoliche gulosa Wiedemann (Tabanidae) is a pollinator of the putative floral model, Pelargonium stipulaceum and its floral mimic, Disa karooica. We document similarities in floral spur/tube length, spectral reflectance, absence of scent, presence of nectar guides, and overlapping phenology and distribution in these two sympatric plant species. We use colour spectrum analyses to test the idea that divergence in flower colour in the D. draconis complex is driven by adaptation to model Pelargonium species of different colours. © 2009 SAAB. Published by Elsevier B.V. All rights reserved.

Abstract: The systematic status of Disa draconis (L.f.) Sw. is revised following extensive field studies of population variation in the Western Cape, South Africa. Principal component and cluster analyses revealed clear distinctions between populations from sandplain, semi-arid and montane environments. Diagnostic characters were found in each of the population clusters indicating the existence of a species complex, rather than a single taxon as in the current taxonomy. We propose, therefore, that the name D. draconis (L.f.) Sw. be restricted to the individuals of the sandplain populations from which the type was collected. We reinstate an earlier name, Disa harveiana Lindl., to describe the montane populations which possess several autapomorphic characters. We also show that the geographical variation in spur length and flowering time within this species can be partitioned into two geographically distinct subspecies: D. harveiana subsp. harveiana and D. harveiana subsp. longicalcarata Johnson & Linder. The populations from the semi-arid Karoo region were recognized as a distinct new species, Disa karooica Johnson & Linder, on the basis of their peculiar petal structure. A cladistic analysis indicated that the three species forming the D. draconis complex form a monophyletic and relatively specialized lineage within Disa sect. Coryphaea. The revised classification also has important conservation implications as D. draconis, previously considered a common species, is now restricted to a few highly threatened populations on the west coast near Cape Town.