A NEW ENDEMIC SPECIES OF BEGONIA ( BEGONIACEAE ) FROM THE SOCOTRA ARCHIPELAGO

The new species Begonia samhaensis, in section Peltaugustia ( Warb.) Barkley, is described from the island of Samha in the Socotra archipelago. It differs from the only other species in the section, B. socotrana Hook.f., in a number of gross morphological characters and is likely to be a relict taxon rather than the result of more recent dispersal and divergence. A revision of sect. Peltaugustia is presented. Detailed surveys have been carried out on both species. The new species has a restricted distribution and a total population of fewer than 1000 individuals, and is recommended to be placed in the IUCN category VU D1, 2. Begonia socotrana has been found in new sites, and is locally common in parts of its range. Its current placing in the IUCN ‘Vulnerable’ category is considered to be unwarranted, and it is recommended that the species should be listed as ‘Least Concern’.

of which it differs chiefly in the male perianth having four segments, in the shorter filaments, rounded top of the anther, the six lobes of the female perianth (instead of five), and the intwisted arms of the style, characters all of which, except the last, occur in the Natal B. geranioides, to which B. socotrana is unquestionably closely allied' (Hooker, 1881).Warburg (1894: 140) considered the species to be distinct enough to warrant the creation of a subsection within Augustia to accommodate it: (translated from German) 'B.socotrana has been placed in a separate subsection Peltaugustia due to it having peltate leaves, one-winged fruit and bulbils on a swollen rootstock.This subsection is transitional with section Reichenheimia'.Although Peltaugustia was not recognized by Irmscher in his monograph of Augustia (Irmscher, 1961), it was elevated to sectional status by Barkley (1972), reflecting its unusual anatomy and isolated position within the genus.
A second species of Begonia from the archipelago was discovered on the island of Samha by an expedition from the Royal Botanic Garden Edinburgh (RBGE) in 1996.Until more recently (1999) the species was known only from a single plant found on the northern side of the highest point of the island, which is a limestone outcrop approximately 50m2.Only bulbils were seen as the plant had died back for the dry season, and it was thought to be B. socotrana.The bulbils were cultivated at RBGE, where it became apparent that the collection represented a new species.Samha could be considered an even less likely place than Socotra in which to find a Begonia, as it reaches an altitude of only 779m.It therefore attracts a reduced amount of moisture in the form of mist and lacks the lush montane vegetation associated with B. socotrana.The new species has been placed in sect.Peltaugustia with B. socotrana as it possesses bulbils and peltate leaves which are the definitive characters of the section, although it is distinct from B. socotrana in a number of gross morphological characters, summarized in Table 1.The morphological differences and the marked divergence in nuclear ribosomal ITS sequences (M.Hughes, unpublished data) suggest the species is relict on the island rather than the result of more recent dispersal and divergence.The distribution of both species is shown in Fig. 1.Observations during RBGE expeditions in 1989, 1990, 1992, 1993, 1996 and 1998 suggested that B. socotrana was more common than the previous publications state, and this prompted detailed surveys of both Begonia species in spring 1999 and 2000.These surveys confirmed that B. socotrana is locally common and has a far wider distribution in the Haggier than stated by Lavranos & Radcliffe-Smith (1969), and still occurs in sizeable populations on the limestone plateaux of Reiged and Rewged, as found by Popov (1957).Part of the reason for the apparent scarcity of the species in 1967 is likely to be the timing of the trip, which occurred in March and therefore coincided with the start of the dry season and the die-back of low altitude populations of Begonia.The threat of grazing seems to have been overstated, given the large size of some of the populations found growing within potential reach of livestock.Goats will eat the leaves, but they are quite acidic and during the wet season there is plenty of other more palatable fodder, which is eaten in preference.Even if grazing pressure were to increase, many of the populations of B. socotrana grow on inaccessible cliffs and outcrops, making it less vulnerable than many other Socotran endemics.Although the area of occupancy for the species is less than 50km2, given the negligible impact of livestock and of collecting by locals and the fact that many populations are inaccessible, it is not especially 'prone to the effects of human activities (or stochastic events whose impact is increased by human activities) within a very short period of time in an unforeseeable future' (IUCN, 1994).Thus, B. socotrana does not meet the criteria for 'Vulnerable' as defined in either the current (IUCN, 1994) or the recommended changed version (IUCN/SSC Criteria Review Working Group, 1999) of the IUCN red list criteria, and we recommend that it should therefore be placed in the 'Least Concern' category.
Begonia samhaensis was also surveyed in detail during spring 1999, and was found to be growing in quite dense groups where conditions were suitable at the original collection site (i.e.north to north-east facing vertical limestone faces or more southern aspects with shading overhangs), and possibly numbering up to 200 individuals.The increase in the number of plants compared with the single specimen seen in 1996 is due in part to the earlier timing of the 1999 trip, which managed to catch the end of the wet season.Approximately 30 more plants were found growing in two new sites on the northern edge of the island's limestone plateau at an altitude of 650m, over 100m lower than the original collection site.This raised the possibility that the vertical cliffs on the northern side of the island might also harbour B. samhaensis, though these are very difficult to survey.However, during the January 2000 expedition, an examination of these cliffs using binoculars failed to reveal any new sites, and it now seems likely that the total area of occupancy is restricted to the three known sites, in an area of 2km by 500m, which probably harbour fewer than 1000 plants.This small total population size and the fact that B. samhaensis exists only in a specific microclimate at the very highest parts of Samha do make the plant prone to the effects of human activities (e.g.livestock herders chewing the leaves) and stochastic events such as those due to climate change.This species should therefore be listed under the IUCN red list criterion VU D1, 2.
R  B .P A revision of sect.Peltaugustia is presented here, in order to include a modified description of the section and to allow comparison to be made between the two species.

A
We thank Vanessa Plana for discovering B. samhaensis, Steve Scott, Fiona Inches and Andrea Fowler for their expertise in maintaining the living collections, Lizzie

323) described the populations as at a 'critically low level'. Both cite overgrazing by goats as the main threat. The latest IUCN Red List of Threatened
Peltaugustia on the Socotra archipelago.Begonia socotrana has been rumoured to be very rare in the wild since an expedition to Socotra in 1967 by Lavranos and Radcliffe-Smith.In their list (Lavranos & Radcliffe-Smith, 1969: 3) the plant was recorded only from two of the highest peaks of the Haggier mountains, and was described as 'not common, but not in immediate danger owing to virtual inaccessibility to man and goat'.In the 1978 IUCN Plant Red Data Book(Lucas & Synge, 1978: 79)it is listed as 'Endangered', based largely upon the information from the 1967 expedition but stating 'the population of this island endemic has reached critically low levels', and citing grazing as the probable cause of its decline.The fact that it was found on only two high peaks in 1967 is highlighted, although reference is made to an earlier expedition by Popov (1957) who found B. socotrana on the Reiged limestone plateau to the west of the Haggier.
F. 1.The distribution of Begonia sect.The listing of B. socotrana in theIUCN Red Data Book (1978)has caused it to be highlighted in other publications on threatened plants.Koopowitz & Kaye (1983:  63)suggested that 'the population of begonias has steadily eroded', and Belousova  & Denisova (1992: Plants ( Walter & Gilliet, 1998: 73)lists the species as 'Vulnerable', a category one step below the 'Endangered' status that the species was awarded in 1978.