We present the first report on somatic chromosome numbers and morphology in eight of 13 recorded species ofCrossostylis, one of inland genera of Rhizophoraceae. The chromosome number ofCrossostylis is 2n=28 in all species examined; therefore, the genus hasx=14, a number which is the smallest and unknown elsewhere in the family. Based onCrossostylis raiateensis, we further present that 24 of 28 chromosomes at metaphase have centromeres at median position, and the remaining four at submedian or subterminal position. The chromosome morphology seems to imply thatCrossostylis might be a tetraploid with the original base numberx=7, but an extensive study in the other inland genera is needed to find such a small chromosome number.