Common name. Mangroves. Family Rhizophoraceae.
Habit and leaf form. Trees. Leaves cauline. Stem internodes hollow. Helophytic (coastlines, estuaries and tidal swamps). Leaves opposite; decussate (A), or not decussate (C); leathery; petiolate; simple. Leaf blades entire; elliptic, or obovate (usually elliptic to obovate); pinnately veined (midrib extended into a caducous point). Leaves with stipules (interpetiolar, lanceolate, reddish). Stipules interpetiolar (sheathing the terminal bud); with colleters (secreting mucilage), or without colleters; caducous (leaves an annular scar). Leaf blade margins entire; revolute (sometimes). Leaf anatomy. Hairs absent. Extra-floral nectaries absent. Stem anatomy. Secondary thickening developing from a conventional cambial ring. Roots. Aerial roots present (aerial roots, stilt roots usually branching and several metres from the trunk).
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Plants viviparous.
Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in cymes (simple or di- or trichasial). The terminal inflorescence unit cymose, or racemose. Inflorescences axillary; inflorescence pedunculate. Flowers ebracteate; bracteolate (broadly ovate, connate at the base forming a cup below the flower); regular; usually 4 merous, or 5 merous. Free hypanthium present (very short and hidden by the bracteoles). Perianth with distinct calyx and corolla; 6–32; 2 -whorled; isomerous. Calyx present; 4; 1 -whorled; gamosepalous; blunt-lobed; valvate; tubular; regular; commonly fleshy (or leathery); persistent. Calyx lobes ovate (to narrowly ovate). Corolla present; 4; 1 -whorled; alternating with the calyx; polypetalous; involute; commonly fleshy. Petals ovate; sessile. Corolla members entire. Fertile stamens present, or absent (rarely — when flowers female, and then there are epipetalous staminodes). Androecial members definite in number. Androecium 8–12. Androecial members free of the perianth (generally inserted on the outer edge of the perigynous or epigynous disk); markedly unequal (subequal in length); free of one another; generally 1 -whorled. Androecium exclusively of fertile stamens. Stamens 8–12 (usually); all more or less similar in shape; diplostemonous (often paired opposite the petals), or triplostemonous, or polystemonous; filantherous, or with sessile anthers. Anthers connivent; dorsifixed; dehiscing by longitudinal valves (large adaxial longitudinal valve); introrse; bilocular (B), or many locular (many small locules); tetrasporangiate. Fertile gynoecium present, or absent (rarely, when flowers male). Gynoecium 2–5(–6) carpelled. The pistil 2 celled. Carpels reduced in number relative to the perianth, or isomerous with the perianth. Gynoecium syncarpous; eu-syncarpous; partly inferior (at least one half inferior). Ovary plurilocular; 2 locular. Gynoecium when G2, median. Epigynous disk present, or absent. Gynoecium stylate. Styles 1; apical. Stigmas 1; 2 - lobed. Placentation usually axile to apical. Ovules 2 per locule; pendulous; epitropous; with ventral raphe; arillate, or non-arillate; hemianatropous, or anatropous.
Fruit and seed features. Fruit coriaceous; indehiscent; a capsule (rarely), or a berry, or a drupe; 1 celled; 1 seeded (usually 1 fertile). Seeds copiously endospermic. Endosperm oily (and fleshy). Embryo well differentiated. Cotyledons 2. Embryo straight. Micropyle zigzag.
Special features. Mangroves.
Geography, cytology, number of species. World distribution: pantropical and subtropical, concentrated in the Old World. 120 species.
Economic uses, etc. Some yield wood used for underwater construction and piling, and tannins are obtained from the bark.
Etymology. From the Greek for "root" and "to bear"; the plant sends down aerial roots from the branches, which act as stays.