1. COMBRETACEAE R. Brown
White Mangrove Family
Walter S. Judd
Trees, shrubs, or lianas, monoecious, dioecious, or polygamous, terrestrial, amphibious, or aquatic, sometimes with erect, monopodial trunk supporting a series of horizontal, sympodial branches, armed or unarmed, not clonal; mucilaginous cells or canals often present in parenchymatous tissues; hairs various, some long, straight, sharp-pointed, eglandular, unicellular, and very thick-walled, with conic internal compartment at base (combretaceous), sometimes hairs also short-stipitate, glandular; roots occasionally with pneumatophores. Stems erect, horizontal, spreading, or prostrate; bud scales absent. Leaves persistent or deciduous, alternate and spiral, or opposite or subopposite and decussate, simple; stipules usually absent, sometimes present and minute; petiolate, petiole or base of blade often with 2 circular to elliptic and flat structures or flask-shaped nectariferous cavities; blade papery to leathery, venation pinnate, secondary veins often forming loops or smoothly arching toward margin, margins entire, surfaces glabrous or hairy; domatia often present as pits, pouches, or hair tufts. Inflorescences terminal and/or axillary, spikes or panicles [racemes]; bracts present (each flower in axil of a usually caducous bract); bracteoles 0 or 2, adnate to hypanthium. Flowers bisexual or unisexual, staminate and pistillate on same or different plants, or bisexual and staminate on different plants, or all bisexual, usually actinomorphic; perianth and androecium borne on hypanthium; hypanthium cupulate, cylindric, or tubular, slightly to conspicuously prolonged beyond ovary and differentiated into 2 parts—proximally adnate to ovary, distally free; sepals 4 or 5, distinct or connate basally, imbricate to valvate; petals (0 or)5, distinct, imbricate or valvate; nectary present, usually a lobed or unlobed disc on top of ovary, often hairy; stamens [4 or]5–10[–16], inflexed in bud; filaments distinct, included to long-exserted; anthers dorsifixed, dehiscent by 2 longitudinal slits; pollen grains 3-colporate, often also with poreless furrows; pistil 2–5-carpellate, carpels connate; ovary inferior [semi-inferior], 1-locular; placentation apical; style 1; stigma 1, punctate to capitate; ovules 2–5[or 6], pendulous on elongate funiculi from apex of locule, anatropous, bitegmic, crassinucellate. Fruits drupes, ribbed and/or winged, dry to spongy or fleshy. Seed 1 per fruit, relatively large, outer portion of seed coat fibrous; embryo with usually 2 folded or spirally twisted cotyledons; endosperm absent.
Genera 11, species ca. 500 (5 genera, 8 species in the flora): s United States, e Mexico, West Indies, Central America, South America, Asia, Africa, Australia; pantropical, warm temperate areas.
Combretaceae are clearly placed within Myrtales, a major angiosperm order whose monophyly is well supported by anatomy, embryology, and morphology (L. A. S. Johnson and B. G. Briggs 1984), as well as by plastid and nuclear DNA sequences (M. W. Chase et al. 1993; E. Conti et al. 1996, 1997; V. Savolainen et al. 2000, 2000b; D. E. Soltis et al. 2000, 2001; K. W. Hilu et al. 2003; Wang H. et al. 2009; O. Maurin et al. 2010, 2017). Morphological characteristics of Combretaceae supporting this placement include vessel elements with vestured pits, stems with internal phloem, stipules absent or present as very small lateral structures, flowers each with a short to elongate hypanthium, stamens incurved in bud, and a single style (W. S. Judd et al. 2008).
C. A. Stace (2007) recognized two subfamilies within Combretaceae: Strephonematoideae Engler & Diels (only Strephonema Hooker f. of western tropical Africa) and Combretoideae Burnett (all remaining genera); DNA-based phylogenetic analyses have supported this distinction (Tan F. X. et al. 2001, 2002; O. Maurin et al. 2010). Within the latter subfamily, two tribes are distinguished: Laguncularieae Engler & Diels (Dansiea Byrnes, Laguncularia, Lumnitzera, Macropteranthes F. Mueller) and Combreteae de Candolle [Combretum, Conocarpus, Finetia Gagnepain, Getonia Roxburgh, Guiera Adanson ex Jussieu, Terminalia]. Phylogenetic relationships within the family are imperfectly understood, and problems of generic circumscription exist (Stace).
Combretaceae are distributed pantropically, with extensions into warm temperate regions; within the geographical coverage of this flora, the species here treated are usually considered to be restricted to Florida; however, Conocarpus erectus and Laguncularia racemosa likely have become established on South Padre Island (Willacy County), Texas (B. L. Turner et al. 2003; Texas Non-Native Plants Group, http://www.texasnonnatives.org). The family is ecologically significant in coastal regions of southern and central Florida due to the presence of the mangrove species Laguncularia racemosa and the mangrove-associate C. erectus. Both occur in extensive coastal stands [along with Avicennia germinans and Rhizophora mangle]. Lumnitzera racemosa is also a mangrove species; it occurs in southern Florida only in a single naturalized population and shows potential to be an invasive species (J. W. Fourqurean et al. 2010). Combretum indicum, Terminalia catappa, T. muelleri, and, probably, T. buceras are also non-native; only the first two are considered invasive. Fruit dispersal in Conocarpus, Laguncularia, and Lumnitzera is by floating in water; the fruits of Terminalia are eaten by mammals and birds; they float and may be secondarily water-dispersed.
Combretaceae are not of great economic importance, although Terminalia buceras, T. catappa, and T. molinetii are widely used as shade trees and/or ornamentals in southern Florida due to their distinctive growth architecture, and cultivars of Conocarpus erectus with densely pubescent leaves are widely used as ornamental shrubs or small trees because of their distinctive coloration and salt tolerance. Terminalia catappa has fruits with edible kernels. Combretum indicum is often grown as an ornamental vine because of its showy flowers, which open white and change to pink and then red as the day progresses.
SELECTED REFERENCES Exell, A. W. 1931. The genera of Combretaceae. J. Bot. 69: 113–128. Exell, A. W. and C. A. Stace. 1966. Revision of the Combretaceae. Bol. Soc. Brot., ser. 2, 40: 5–25. Graham, S. A. 1964. The genera of Rhizophoraceae and Combretaceae in the southeastern United States. J. Arnold Arbor. 45: 285–301. Stace, C. A. 1965. The significance of the leaf epidermis in the taxonomy of the Combretaceae. Bot. J. Linn. Soc. 59: 229–252. Stace, C. A. 2004. Combretaceae. In: N. P. Smith et al., eds. 2004. Flowering Plants of the Neotropics. Princeton. Pp. 110–111. Stace, C. A. 2007. Combretaceae. In: K. Kubitzki et al., eds. 1990+. The Families and Genera of Vascular Plants. 15+ vols. Berlin etc. Vol. 9, pp. 67–82. Stace, C. A. 2010. Combretaceae. In: Organization for Flora Neotropica. 1968+. Flora Neotropica. 121+ nos. New York. No. 107.