Leaf thickness of mangroves (Rhizophora mangle) growing in different salinities

Leaf thickness and fresh-weight to dry-weight ratio of leaves of Rhizotphora mangle L. were higher in plants growing at sites of constant high salinity than at sites of fluctuating salinity. Thick leaves had more water storage tissue than thin leaves. It is hypothesized that water storage tissue play a role in osmoregulation. MANGROVES GROW IN DIFFERING SALINITY regimes, from marine to fresh water. Those of the genus Avicennia have salt-excreting glands on the leaves (Mullan 1931) whereas in Rhizophora, which does not have salt-excreting glands, the amount of salt entering the vascular system seems to be regulated by a mechanism located in the roots (Scholander et al. 1962). The ability to store water is widespread among mangroves (Mullan 1931). Uphof (1941) listed six genera containing water storage tissue in the leaves. The function of this tissue in mangroves is unknown, although in species with salt-excreting glands it seems to be less developed than in species without salt glands (Macnae 1968). We can speculate, therefore, that the water storage tissue of mangroves may play a role in osmoregulation. If this is true, we would expect the degree of succulence to be different in plants derived from places of different salinities. In this paper, leaves from trees of Rhizophora mangle growing in areas with different salinity regimes are compared.