Wild orchids The winter rainfall species

Fire is an important element in orchid ecology. Most orchids flower profusely in the first season after a fire when competition for sunlight and moisture is reduced, writes Cameron McMaster.
Issue date : 29 August 2008

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The winter rainfall region in SA is confined to the southwestern part of the country, but some rain falls in summer along the southern coast and especially in the eastern extremity of the region. The vegetation types consist of sand-plain vegetation along the west and south coast, and fynbos on sandstone-derived soils along the mountain chains and alkaline soils derived from marine deposits on the Agulhas plain and the southern coast.

Lowland plains between the mountains consist mostly of clay soils derived from shale and support Renosterveld vegetation which is particularly rich in geophytes (bulbous plants including orchids). W ith such a diversity of soil types and topography it’s not surprising the winter rainfall region has by far the largest number of orchid species of any region in SA. Most are endemic, occurring exclusively in the winter rainfall region, but a few extend into the eastern and northern parts of SA. Within each vegetation type there are many microhabitats supporting local species with highly restricted distribution – species that are vulnerable and in danger of extinction should their habitat be destroyed or degraded. he vast majority of orchids are terrestrial and deciduous, well adapted to winter growth and a spring to mid-summer flowering cycle.

However, some are evergreen, particularly species adapted to wetland areas, seepages and streams. F ire is an important natural phenomenon in both fynbos and Renosterveld and it’s a very important element in orchid ecology. Fires can occur at variable intervals with an average interval of 10 to 15 years. Most orchids are stimulated to flower profusely in the first season after a fire when competition for sunlight and moisture from surrounding vegetation is reduced.

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A mythical association
The genus Satyrium also contains a number of spectacular and colourful orchids. Satyriums have prominent spikes of many small flowers, each with two spurs which are the feature the genus is named after – the satyr is a Greek mythical character with a human body and head, two horns and the hips and feet of a goat. The large, dark-pink Satyrium carneum which occurs commonly in the Strandveld on the Agulhas plane in spring, is one of the most spectacular. A similar, but rarer and more localised scarlet species, Satyrium princeps, occurs near Knysna and is severely threatened by urban sprawl and alien invaders.

Satyrium neglectum is another showy pink species widespread in Renosterveld, but more than 90% of its original habitat has been transformed by agriculture. Satyrium coriifolium is an orange species that’s adapted well to habitat transformation and has been able to colonise disturbed areas along roadsides. Its range extends eastwards as far as Port Elizabeth. It’s particularly evident along the N2 between Grabouw and the Bot River in spring. Acrolophia is a genus of evergreen orchid with persistent tough, leathery leaves and spikes of rather dull, small flowers. While surveying sites near Natures Valley last year CREW discovered three plants of one of the most striking members of the genus, Acrolophia lunata. Originally described from the Langeberge this elusive species, with a tall inflorescence of small white flowers, had not been seen for many years (see the June 2008 issue of Veld and Flora, published by the Botanical Society of SA).

When so much attention is focused on only three particularly rare species, the role farmers and landowners play in conservation becomes understandable. The few species mentioned in this article are a tiny sample of the many hundreds of beautiful wild orchids, many populations of which have already disappeared forever. – Cameron McMaster ([email protected]) |fw