The genus Rhizophora in Suriname

The peculiar distribution of the species of Rhizophora (Rhizophoraceae) is wellknown. Floras and manuals usually mention one western species — R. mangle L. — that occurs both in the coastal regions of tropical and subtropical America and in the corresponding habitats of west tropical Africa, and an eastern species — R. mucronata Lam. — occurring both in tropical Asia and in east tropical Africa. It is also well-known that a few other species occur in tropical Asia; a recent revision has been given by Hou (1958). G. F. W. Meyer (1818) described from British Guiana a second American species, R. racemosa, differing in the inflorescence which is forked and 2-flowered in R. mangle and much-branched in R. racemosa. Enoler (1876) regarded this species as a variety of R. mangle; most botanists, however, considered it synonymous with the latter. Leechman (1918) published an investigation of the Rhizophoras of Georgetown, British Guiana. He found not only the two species of Meyer but also a third species, R. harrisonii Leechm., provided with a much-branched inflorescence as in R. racemosa. The hypocotyls (also considered radicles) of both R. mangle and R. harrisonii reach a length of up to 30 cm, that of R. racemosa a length of up to 65 cm. The opinion of most botanists, however, remained unchanged: namely that the material of the genus Rhizophora from both America and West-Africa belongs to one species, R. mangle L. In treating the Rhizophoraceae for the Flora of Suriname I shared this opinion (Jonker, 1942). In 1953, however, Keay published his revision of the West-African Rhizophoras based on field observations. He concluded that the three species recognized by Leechman also occurred in West-Africa. Savory (1953) studied the ecology of Rhizophora in Nigeria and found that the most common species is R. racemosa, a pioneer at the outer border of the Rhizophora zone. R. harrisonii is dominant in the middle region and R. mangle in the interior part of the zone. The latter has the highest salt tolerance and occurs in the habitats with the highest salt concentration in the dry season. The other species obtain, especially in the wet season, more fresh water.