Biodiversity among West African Rhizophora: Foliar wax chemistry

Foliage from 21 red mangroves (Rhizophora mangle, R. racemosa and R. x harrisonii) from different ecogeographic conditions in Gabon, West Africa, was analyzed for epicuticular wax composition using CC, GC and GC-MS. Aliphatic hydrocarbons ranging from C-23 to C-34 and some triterpenoids were identified. Alkanes were the major constituents (46.7-99.9%), with triterpenoids also accounting for up to 53.3% of the wax extract. High contents of octacosane (27.2%) and lower amounts of nonacosane (14.9%) and hentriacontane (9.8%) distinguished R. mangle from the other two species. R. hizophora x harrisonii was exceptionally rich in nonacosane (45.3%) with moderately high concentrations of hentriacontane (25.4%), whereas R. racemosa was intermediate between the two former species in its content of these three alkanes. Inclusion of the less abundant constituents in principal components analysis provided a good separation of R. x harrisonii, whereas the two other species showed some degree of overlap. Although major alkane patterns can be used to discriminate among the Rhizophora species examined, we do find substantial intra-specific variation that may be attributable to population genetic variation; this was least for R. x harrisonii. The hybrid status of this latter species could not be confirmed from the biochemical analyses carried out.