The families of flowering plants.
Habit and leaf form. Bitter trees, or shrubs. Leaves evergreen; small to medium-sized; opposite; simple. Lamina entire; conspicuously asymmetric; cross-venulate. Leaves exstipulate. Lamina margins entire, or dentate.
Leaf anatomy. Stomata present; mainly confined to one surface (abaxial); anomocytic.
Adaxial hypodermis present. Lamina dorsiventral. The mesophyll containing calcium oxalate crystals. The mesophyll crystals druses.
Stem anatomy. Cork cambium present; initially deep-seated. Nodes unilacunar (with one trace). Xylem with tracheids. Vessel end-walls oblique; scalariform.
Reproductive type, pollination. Plants hermaphrodite.
Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; when aggregated, in cymes (few flowered). The ultimate inflorescence unit cymose. Inflorescences terminal. Flowers two bracteolate; somewhat irregular; somewhat zygomorphic; cyclic; tetracyclic. Free hypanthium present.
Perianth with distinct calyx and corolla; (8–)10(–16); 2 whorled; isomerous. Calyx (4–)5(–8); 1 whorled; somewhat gamosepalous, or polysepalous; persistent; slightly imbricate, or valvate; with the median member anterior. Corolla (4–)5(–8); 1 whorled; gamopetalous. Corolla lobes markedly longer than the tube (the tube very short). Corolla imbricate; almost rotate; sub-irregular; yellow.
Androecium 2. Androecial members adnate (attached near the base of the corolla); markedly unequal; free of one another; 1 whorled. Androecium exclusively of fertile stamens. Stamens 2; reduced in number relative to the adjacent perianth; oppositisepalous (alternate with the posterior and lateral lobes); alternating with the corolla members; filantherous (with short, stout filaments). Anthers connivent; with a broad connective; dehiscing via longitudinal slits; bilocular (large, the pollen sacs undulately plicate and twisted). Pollen grains aperturate; 3 aperturate; colporate.
Gynoecium 2 carpelled. Carpels reduced in number relative to the perianth. The pistil 1(–2) celled. Gynoecium syncarpous; eu-syncarpous; inferior. Ovary1 locular (incompletely partitioned). Gynoecium median. Epigynous disk absent. Gynoecium stylate. Styles 1 (short, thick); apical. Stigmas 2 lobed, or 4 lobed (broad). Placentation parietal (the the intruded placentas almost meeting, constituting partial partitions). Ovules in the single cavity 20–50 (‘many’); ascending; anatropous; unitegmic; tenuinucellate.
Fruit non-fleshy; dehiscent; a capsule. Capsules septicidal and valvular. Seeds copiously endospermic. Embryo well differentiated (though small). Cotyledons 2. Embryo straight.
Physiology, biochemistry. Not cyanogenic. Iridoids not detected. Proanthocyanidins absent. Aluminium accumulation not found.
Geography, cytology. Neotropical. Tropical. Northwestern South America.
Taxonomy.Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Corniflorae; Dipsacales (re-assigned). Cronquist’s Subclass Rosidae; Rosales. APG 3 core angiosperms; core eudicot; Superorder Asteranae; campanulid; Order Bruniales.
Species 8. Genera 1; only genus, Columellia.