It is Sugar Loaf Mountain in Rio de Janeiro. Everybody knows it and he shares its typical biological elements with thousands of other inselbergs around the globe.
Inselbergs consist of large expanses of rocky slopes which on the first look seem to be bare. However, they comprise an astonishing diversity of life. Globally inselbergs are characterized by a typical set of habitat types and plant communities. The extent of their presence on individual inselbergs varies between tropical and temperate regions. In the following a brief description of selected inselberg specific habitat types and plant communities is given.
Looking at inselbergs from a distance they usually have a greyish or brownish colour. This colouration is due to cryptogams which form a nearly continuous biofilm on all exposed rocks. They form an epilithic and partly also endolithic cryptogamic crust that consists of cyanobacteria, lichens and fungi. These organisms are extremely tolerant to heat, high rates of irradiation and survive complete desiccation.
Solutional processes on mostly flat rocky surfaces have caused the development of depressions of various sizes and depths. Rock pools can be filled with water for several days up to many weeks during the rainy season. They may contain highly specialized aquatic plants. Rock pool specialists are adapted to cope with the unpredictability of prolonged droughts. Among rock pool specialists there are members of various angiosperm families such as Aponogetonaceae (Aponogeton), Cyperaceae (Cyperus), Haloragaceae (Myriophyllum), Linderniaceae (Lindernia), Lythraceae (Rotala) and Scrophulariaceae (Dopatrium). Moreover, the fern-like genus Isoetes (Isoetaceae) contains a number of species that exclusively occur in rock pools. These only seasonally available aquatic habitats show a large degree of spatial and temporal dynamics (i.e. species turnover) making it difficult to predict their inventory over longer periods. In tropical Africa so-called grinding holes are widespread on inselbergs which originated in the past due to human activities (i.e. grinding of cereals). Grinding holes often have an oval shape with a length of 20-30cm. Nowadays they form man-made habitats that are colonized by aquatic plants, amphibians and insect larvae.
On many tropical inselbergs mat-forming monocots occur. The mats formed by them are literally glued to the underlying rock and can be lifted (with the use of force) like a carpet. Often mats are circular in outline and reach a diameter of a few meters. Many prominent mat-formers are desiccation-tolerant and possess a shrub or tree-let like habit. Particularly important are members of Cyperaceae (Trilepideae: Afrotrilepis, Coleochloa, Microdracoides, Trilepis) and Velloziaceae (Vellozia, Xerophyta). Remarkably they show a Gondwanan type of distribution with southeastern Brazil, east Africa and Madagascar being centers of their diversity. Their stems mainly consist of adventituous roots that possess a velamen radicum (a tissue consisting of dead rhizodermis cells). Its function is the rapid absportion of water during rainfall. Both in South America and Africa the stems of desiccation-tolerant Cyperaceae and Velloziaceae offer growth sites for highly specialized epiphytic orchids. Only recently it could be shown that certain Poaceae are desiccation-tolerant mat-formers on inselbergs too. In different parts of India the genus Tripogon forms mats on rock outcrops and research on them is currently underway. One of the most important mat-formers on Malagasy inselbergs is Styppeiochloa hitchcockii. It had been overlooked up to now that this species is desiccation-tolerant too. Likewise desiccation-tolerant and mat or cushion forming (but not glued to the underlying rock) are different species of Borya (Boryaceae) on Australian inselbergs. They too have stems mainly consisting of adventitious roots with a velamen radicum. On South American inselbergs numerous bromeliads (e.g. species of Alcantarea, Encholirium, Pitcairnia, Tillandsia, Vriesea) are very prominent mat-formers. They are not desiccation-tolerant but possess succulent leaves (e.g. Encholirium) or store water externally in tanks (e.g. Alcantarea). Frequently, the bromeliads occur in multi-species mats in which they grow together with desiccation-tolerant species and cacti (e.g. Coleocephalocereus spp.). Certain members of Vriesea exclusively colonize steep vertical rocky slopes and are not to be found on only gently inclined slopes. Despite not belonging to the angiosperms it is worth mentioning that the fern-ally Selaginella (Selaginellaceae) is present with desiccation-tolerant mat-formers on inselbergs in temperate (e.g. southeastern USA) and tropical regions (both in the neotropics and paleotropics). Well known examples from Brazil are S. convoluta and S. sellowii.
On slightly inclined rocky slopes an EFV community is present during the rainy season. This community develops over very shallow substrates where seepage water is available for several weeks or months. Typically the substrate is not only shallow but nutrient poor. The floristic richness of EFV can be very high (in parts of tropical Africa and Madagascar). Particularly typical are families such as Eriocaulaceae, Xyridaceae and the carnivorous Droseraceae and Lentibulariaceae. Most of their species are short-lived annuals which form a seed bank in the dry season. In addition, geophytes can be richly represented. Most of all EFV communities on Malagasy inselbergs are very rich in geophytic orchids. On the peak of the rainy season numerous species of e.g. Disa, Cynorkis and Habenaria offer a rich display of colourful flowers. Frequerntly overlooked are members of the fern-like genera Isoetes (Isoetaceae) and Ophioglossum (Ophioglossaceae). Members of the Lentibulariaceae (Genlisea spp., Utricularia spp.) possess highly sophisticated subterranean traps for attracting, catching and digesting prey. Of particular interest is the fact, that certain species of Genlisea (e.g. G. margaretae) and Utricularia (e.g. U. gibba) are known to have the smallest genomes within angiosperms, i.e. even smaller than the genome of Arabidopsis thaliana.