The orchids of Mauritius have not been well studied and little is known about their reproductive biology. Eighty-nine species have been described of which nine are endemic: however, twenty-four species have been extirpated or have become extinct (Strahm & Bosser, 1996).

These figures will undoubtedly change as we learn more about these orchids. Recent studies I have been conducting suggest there are other taxa to be described from Mauritius and a number of species are in decline. The main focus of my studies is on the reproductive biology and conservation of Mauritian orchids.

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The rarest of the orchids on Mauritius is the epiphytic Angraecum cadetii, which is reduced to only thirteen known individuals, of which four are flowering plants, none of which have produced seed in the last two seasons. Angraecum cadetii Bosser belongs to the section Hadrangis, whose members are endernic to the Mascarene Islands. It was described in 1987 and named after the Reunion botanist Th. Cadet, having been confused with the Reunion endemic A. bracteosum for many years.

On Reunion, A. cadetii occurs in the humid forests around St. Philippe from 300-1000m, where it is described as rare (Bosser, 1987). The situation on Mauritius is much more critical. 11 were once found in the South-West of Mauritius in and around an area called Les Mares. This region was once covered in Pandanus marsh, heathland and patches of Sideroxlon thicket, which supported numerous species of orchids, many of which were found only in these vegetation types. Unfortunately, much of this area in the wet uplands was cleared for the planting of softwoods beginning in 1967, and during the early 1970s, extended to les Mares, the last known stronghold for A. cadetii. Between 1973 and 1981, 30.6km2 of Les Mares was cleared for softwood forestry under the auspices and finance of the World Bank.

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Fortunately much of what little remains is found within the boundaries of the Black River Gorges National Park. However, the region has been invaded by aggressive exotic plant species, particularly the Strawberry Guava Psidium cattleianum, which srnothers out the native vegetation and prevents regeneration, resulting in monotypic stands of guava. As a result of this habitat destruction and degradation, only 13 individuals of A. cadetii are now known, making it probably the rarest of the Mauritian orchids.

Fruit success has been non-existent since I started my studies but there is some hope that the species can reproduce without human intervention, since pollinia removal has been observed. However, flower and plant density is so low that the probability of the pollinator removing pollinia and then depositing them successfully is very slim. Studies on artificial pollination and micro-propagation have begun. Collecting of native orchids is cornparatively rare.

Since A. cadetii is not showy, poaching is not a threat to its survival. Clearly however, without some urgent intervention this species could well become ex tinct on Mauritius in a few years.

Les inflorescences apparaissent à l'aisselle des feuilles, elles sont déclinées (nutantes), longues de 5 à 15 cm. Le pédoncule, flexueux, robuste est long de 2 à 5 cm et est recouvert de 4 à 6 gaines. A l'extrémité de cette hampe florale se trouvent 2 à 5 fleurs (en général 2) verdâtres. Des bractées engainantes recouvrent la majeure partie de l'ovaire. Lorsqu'elles vieillissent, les extrémités des pièces florales deviennent blanches. Les sépales (1 à 1,3 cm de longueur, 0,8 à 0,9 cm de largeur à la base) sont recurvés et épais. De plus, les sépales latéraux sont ornés d'une carène. Les pétales sont plus petits (0,9 à 1 cm de longueur et 0,7 à 0,8 cm de largeur). Le labelle vert sacciforme (1cm x 0,8 cm) se présente sous la forme d'une coupelle dont le fond est prolongé par un éperon vert court et charnu. L'ovaire à six côtes est aussi grand que le limbe (long de 1 à 1,2 cm). Cette espèce, décrite tardivement, est néanmoins assez commune dans des forêts hygrophiles de basse et moyenne altitude (de 3OO à 1200 m). Elle est également présente à Maurice (au centre). Elle est donc indigène des Mascareignes. Les trois espèces principales de la section ne sont pas faciles à distinguer lorsqu'elles ne sont porteuses ni de fleurs ni de hampes florales défleuries. L'observation attentive des feuilles (aspect, forme, stries) permet néanmoins de les distinguer. A. Jubault

References

Bosser, J. 1987. Cuntribution à l'etude des Orchidaceae de Madagascar et des Mascareignes. XXII. Adansonia 3: 249-254.

Strahm. W, and JM Bosser 1996. Mascarene Islands pp. 107-108 in Higsater. E. and V. Dumont. (Eds). Orchids -- Status Survey. and Conservation Action Plan IUCN, Gland, Switzerland and Cambridge, UK.

Cadet,Th. Fleurs et Plantes de la Réunion et l'ile Maurice, Papeete-Tahiti 1983, 132 pp.

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