Molecular identification of natural mangrove hybrids of Rhizophora in Peninsular Malaysia

Natural hybridization is common in plants. Very often, the identity of a putative hybrid is inferred based on the observation of morphological features intermediate between two possible parental species occurring in a specific location. However, due to plasticity of morphological features and the co-occurrence of more than two possible parental species, molecular markers would be most useful to establish the origin of a putative hybrid. In mangroves, three Rhizophora species (Rhizophora apiculata, Rhizophora mucronata, and Rhizophora stylosa) and two putative hybrids (Rhizophora × lamarckii and Rhizophora × annamalayana) are distributed in the Indo-West Pacific region. Leaf samples of Rhizophora were obtained from two locations in Peninsular Malaysia, namely, Bagan Lalang and Pulau Burung, where all three species grow in sympatry. We analyzed sequences of one chloroplast and six nuclear DNA regions. Our results confirmed earlier claims that the morphologically identified putative hybrids growing in Pulau Burung are R. × lamarckii, a cross between R. apiculata and R. stylosa. Our data also pointed to the possible discovery of a new Rhizophora hybrid—a cross between R. mucronata and R. stylosa—the identification of which would have been difficult based on morphological features alone. The directions and the stages of hybridization are also discussed.