Carolinea 76

W irth et al .: Biota in a Renosterveld vegetation habitat 53 Galenia africana , Gymnosporia heterophylla , Oederia squarrosa , Olea europaea, Searsia reh­ manniana . The lichen vegetation on soil is not very rich in species; it is confined to rather stable patches of naked loamy soil. Quite frequent are a species of the Psora crenata- group (Fig. 8), Xanthoparme­ lia amphixanthoides (Fig. 12) with its cushions of very small lobed thalli, X. molliuscula (Fig. 22) the very broad-lobed X. leonora (20) and the brown X. cafferensis (Fig. 13). In the vicinity of rocks some of the species, especially Xanthoparmelias may spread from rock to soil (as X. phaeophana ) and vice versa, or from bark to rock, as in Usnea rubicunda or Parmotrema cooperi . The quartz rocks are usually coloured by the pale greenish thalli of Xanthoparmelia species, such as X. marroninipuncta . On top of the rocks, one often encounters X. capensis , together with X. phaeophana , the latter being the most frequent representative of the genus in southern Africa according to H ale (1990). Associated with typical foliose Xanthoparmelia -species are species from the same genus with thalli which resemble placo- dioid crustose lichens strongly appressed to the rock surface, which formerly were assigned to the genus Paraparmelia ( X. condyloides, X. pro­ lata ). Steeper faces bear Caloplaca haematodes which colours the corresponding areas deep red. Most crustose species are inconspicuous and of a greyish to brownish color, as in the quite com- mon Buellia cf. stellulata, Lecidea terrena, Diplo­ schistes euganeus. Usually parts of the quartz rocks are naked, showing that colonisation of that hard, nutrient-poor substrate is also difficult for lichens. The colonisation by foliaceous lichens in semi-arid environments may occasionally be interrupted by fires (which form a natural part of the cycle in this region). Similarly, parts of the carpet-like covers of some fast growing species such as Xanthoparmelia phaeophana may drop during storms and heavy rainfalls. The epiphytic vegetation houses also some fruti- cose species which are typically associated with twigs, such as beard lichens of the genus Usnea , and Teloschistes ( T. flavicans, Usnea rubicunda ) and species with flattened to strap-shaped lobes, such as the greenish Ramalina celastri and the Golden-eye lichen ( Teloschistes chrysophthal­ mus ) with its yellow-grey thalli and orange fruiting bodies. The thicker stems are covered mainly by grey foliose species of the genera Parmotrema, Hypotrachyna, Heterodermia , together with the yellowish Flavoparmelia soredians and Flavopar­ melia rutidota and crustose species as Haema­ tomma persoonii , easily recognizable by its deep red fruiting bodies with white margins. All these species may also colonize small twigs. 6 Discussion Habitually the lichen vegetation of Haarwegkloof Renosterveld Reserve on soil and on rock sur- faces is dominated by foliaceous thalli of the ge- nus Xanthoparmelia s.str., which is characterized by the pale yellowish green to grey green color of the upper thallus surface. Fourteen species were identified in the small study area. Some species may cover several square meters. The genus (sensu stricto, H ale 1990) which is most abundantly represented in semi-arid regions has an evolution center in South Africa containing ca. 250 species. A taxonomical concept of the genus on a molecularphylogenetic basis also in- cludes brown species of the former genus Neo­ fuscelia which is represented by three species in the Renosterveld reserve and Paraparmelia which is represented by four species. It is pre- dicted that several additional species will be found on forthcoming visits to the reserve. The dominance of Xanthoparmelia within the in- vestigated area is not a peculiar characteristic of renosterveld vegetation; it is equally characteri- stic to fynbos vegetation, even for that in the Ce- derberg mountains or in Namaqualand. However, the species composition is considerably different in the Overberg-region. Other foliose genera do not play any considerable role on rock surfaces. Occasionally Parmotrema species from mainly epiphyte habitats also oc- cur on rock surfaces. Apart from Xanthoparmelia the epilithic communities are built up by crustose species, mainly from the genera Buellia , Leci­ dea , Diploschistes and Acarospora . Characte- ristic for dry habitats are yellow representatives of the latter genus, which is well represented in South Africa ( M agnusson 1933). As trees with thick stems are missing in the renosterveld vegetation, epiphytes are confined to twigs and the relatively thin stems of shrubs. Consequently the spectre/amplitude of ecological potentials is quite limited with regard to substrate and climatic quality.Thick bark with deep crevices which guarantee microhabitats protected against rain are missing, as are bark types with spongy, water storing properties. Only the bright yellow to yellow-green powdery crusts of Chrysothrix xanthina represents the ombrophobous life type.