Open Access

Jan-Peter Frahm

• The are three groups of islands in the Indian Ocean east of Africa, which are very different regarding their size, elevation, geological age and number of mosses and liverworts. Mauritius is situated 900 km E of Madagascar on 21°S and consists of volcanic rocks which originated about 8 million years ago. The island is relatively small, about 60 km from W to E and 80 km from N to S, and also relatively low with only a few mountains reaching 800 m altitude. Due to massive habitat destruction and deforestation, the natural forest is almost totally destroyed. Already Renauld (1897) stated "l'extension des cultures a forcément diminué la richesse de la vegetation spontanée". The lower altitudes are almost totally converted to sugar cane plantations. The largest semi-natural part of the island is the Black River National Park in the SW of the island, a high plateau with partial swampy forests, which is eroded by deep gorges. The SE flanks face the wind clouds and receive precipitation of up to 4000 mm or more. The NW parts are distinctly drier, particularly the higher mountains in the NW part of the Island (Le Pouce and Pieter Botha). The vegetation in the higher parts consists of a secondary growth of Sideroxylon bush which is partially forested with Pinus and Eucalyptus. A bryophyte flora of Mauritius was published by Tixier & Guého (1997), which is unfortunately no more available. The moss flora was treated by Frahm et al. (2009) and Een (2009). It consists of 238 species, as compared with 158 species of liverworts included in the checklist of the East African Island by Grolle (1995), updated by Wigginton (2009). (For comparison: Madagascar has 372, Réunion 260, Rodriguez 27, the Seychelles 108, the Comores 143 liverwort species). Réunion is situated 170 km E of Mauritius at the same latitude (between 20° and 21°S). It is with 2511 km2 only slightly larger as Mauritius but with 3069 m much higher. It is with 2 mya also much younger than Mauritius. Due to the steepness, natural habitats in the interior of the island are in a good state of conservation with the only exception of the coastal and lowland regions, which are densely populated. A checklist of the mosses and liverworts of Réunion was published by Ah-Peng & Bardat (2005), additional notes on the mosses by Frahm (2010). Mauritius and Réunion are comprised as the Mascarenes Islands. Further north are the Seychelles, which reach 4° S and thus almost the equator. They consists of 115 Islands, which are dispersed within 400.00 m2 in the Indian Ocean north of Réunion and Mauritius. They are usually divided into the Inner and Outer Islands. The Outer Islands comprise of the Amirantes; Alphonses; Farquhar Islands and Aldabra Islands. Only six species of mosses are known from some of the Aldabra Islands. The Inner Islands consists of 42 granitic islands and two coral islands (Bird Island, Denis Island). The granitic islands are part of the former Gondwana continent and have never been submerged during their geological history. After the split of the Gondwana continent, the Seychelles remained attached to India until 65 mya. Amongst the granitic islands, Mahé, Praslin, Silhoutte and La Digue are the largest and the most visited ones by bryologists, the others are much smaller.