Bruguiera (Rhizophoraceae) in the Indo-West Pacific: a morphometric assessment of hybridization within single-flowered taxa

The first putative hybrid tree species of the genus Bruguiera (Rhizophoraceae), B. × rhynchopetala, is reported from mangrove forests of China and Australia. It was described from China previously as a variety of B. sexangula. The hybrid is acknowledged as B. gymnorhiza × B. sexangula with parent species restricted to different parts of the Indo-West Pacific. The hybrid is recognised at north-eastern and south-eastern parts of the overlap area between parent distributions, but it appears absent in western parts. Further local assessments are needed across the range. Hybrid status is supported by: 1) intermediate and shared morphological characters; 2) distribution limited to areas of co-occurrence of B. gymnorhiza and B. sexangula; and 3) molecular studies. However, compared with other mangrove genera with naturally occurring hybrids, this occurrence is unusual since this intermediate usually has functional flowers and fruits. Full descriptions are given for the new hybrid taxon and three larger, single-flowered Bruguiera taxa, along with distribution maps and a key.