The families of flowering plants.
Habit and leaf form. Trees, or shrubs, or lianas (with stilt- or aerial roots); laticiferous (rarely, the laticifer system restricted to the bark), or non-laticiferous and without coloured juice. Self supporting, or epiphytic, or climbing. Leaves alternate; simple, or compound (or almost so). Lamina deeply dissected to entire; when dissected, pinnatifid, or palmatifid; pinnately veined, or palmately veined; cross-venulate. Leaves stipulate; becoming compound from primordial lobes.
Leaf anatomy. Stomata present; anisocytic (Poikilospermum).
Adaxial hypodermis commonly present. Cystoliths present (e.g. Poikilospermum), or absent (?). The mesophyll containing calcium oxalate crystals. The mesophyll crystals often druses.
Stem anatomy. Nodes bilacunar, or penta-lacunar (?). Secondary thickening developing from a conventional cambial ring. Xylem with vessels. Vessel end-walls simple. Vessels without vestured pits. Primary medullary rays mixed wide and narrow. Wood parenchyma paratracheal.
Reproductive type, pollination. Fertile flowersfunctionally male and functionally female. Plants monoecious. Pollination anemophilous, or entomophilous.
Inflorescence, floral, fruit and seed morphology. Flowers small; regular; 2–4 merous; cyclic. Free hypanthium absent.
Perianthsepaline; 2–4; 1 whorled. Calyx 2–4; 1 whorled; polysepalous, or gamosepalous.
Androecium 2–4. Androecial members free of the perianth; free of one another; 1 whorled. Androecium exclusively of fertile stamens. Stamens 2–4; isomerous with the perianth; erect in bud (the filaments straight). Anthers dehiscing via longitudinal slits; tetrasporangiate. Pollen grains aperturate; 2 aperturate; porate.
Gynoeciumostensibly 1 carpelled. Carpels reduced in number relative to the perianth. The pistil 1 celled. Gynoecium monomerous (ostensibly), or syncarpous (supposedly pseudomonomerous); of one carpel (ostensibly), or eu-syncarpous (if presumed to be pseudomonomerous); superior. Carpel stylate; apically stigmatic; 1 ovuled. Placentation of the single carpel, if so interpreted, basal (or almost so). Ovary 1 locular. Gynoecium stylate. Styles 1; apical. Stigmas 1. Placentation basal. Ovules in the single cavity 1; ascending;more or less orthotropous; bitegmic; crassinucellate.
Fruit fleshy to non-fleshy. The fruiting carpel indehiscent; nucular, or drupaceous. Fruit if viewed as syncarpous, indehiscent; a drupe, or a nut. Gynoecia of adjoining flowers commonly combining to form a multiple fruit (cf. Moraceae). Embryo well differentiated. Cotyledons 2. Embryo straight.
Physiology, biochemistry. Proanthocyanidins present; cyanidin. Flavonols absent. Ellagic acid absent (Cecropia). Saponins/sapogenins absent.
Geography, cytology. Neotropical. Sub-tropical to tropical. Tropical America. X = 7.
Taxonomy.Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Malviflorae; Urticales. Cronquist’s Subclass Hamamelidae; Urticales. APG 3 core angiosperms; core eudicot; Superorder Rosanae; fabid; Order Rosales (as a synonym of Urticaceae).
Species 275. Genera 6; Cecropia, Coussapoa, Myrianthus, Musanga,Poikilospermum, Pourouma.