Family Bixaceae

Bixaceae Link

Excluding Cochlospermaceae, Diegodendraceae

Habit and leaf form. Small trees, or shrubs; with coloured juice (red or yellow). Leaves alternate; long petiolate; simple. Lamina entire; palmately veined. Leaves stipulate.

Leaf anatomy. Stomata mainly confined to one surface (abaxial); anomocytic.

Lamina dorsiventral; with secretory cavities. Secretory cavities with dark, refractive contents; schizogenous. Minor leaf veins without phloem transfer cells.

Stem anatomy. Secretory cavities present (in the pith). Cork cambium present; initially superficial. Nodes tri-lacunar. Secondary thickening developing from a conventional cambial ring. The secondary phloem stratified into hard (fibrous) and soft (parenchymatous) zones. Xylem with fibre tracheids; with vessels. Vessel end-walls simple. Vessels with vestured pits. Wood storied; parenchyma apotracheal.

Reproductive type, pollination. Plants hermaphrodite.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’. The ultimate inflorescence unit cymose. Inflorescences terminal; terminal thyrses. Flowers medium-sized (showy); regular. Hypogynous disk absent.

Perianth with distinct calyx and corolla; 10; 2 whorled; isomerous. Calyx 5; 1 whorled; polysepalous; regular; not persistent; contorted. Corolla 5 (the petals large, with no basal scale); polypetalous; imbricate; regular.

Androecium 50–150 (‘many’). Androecial members branched (from five trunk bundles); maturing centrifugally; free of the perianth; free of one another. Androecium exclusively of fertile stamens. Stamens 50–150 (‘many’); polystemonous; filantherous (the filaments elongated). Anthers dehiscing via pores to dehiscing via short slits (the horseshoe-shaped anther interpreted as folded, so that the morphologically central opening, being on the bend, is ostensibly terminal); tetrasporangiate (but ostensibly octosporangiate, through folding). Endothecium developing fibrous thickenings. Anther epidermis persistent. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral (usually), or decussate. Anther wall initially with one middle layer, or initially with more than one middle layer. Tapetum glandular. Pollen grains aperturate; 3 aperturate; colporate; 2-celled.

Gynoecium 2–4 carpelled. Carpels reduced in number relative to the perianth. The pistil 1 celled. Gynoecium syncarpous; eu-syncarpous; superior. Ovary 1 locular. Gynoecium stylate. Styles 1 (elongate, recurved in the bud); apical. Stigmas 1. Placentation parietal. Ovules in the single cavity 30–150 (‘many’); arillate, or non-arillate (?—the seeds ‘with fleshy red papillae forming an arilloid mass); anatropous; bitegmic; crassinucellate. Outer integument contributing to the micropyle. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; ephemeral. Synergids hooked. Hypostase present (weak). Endosperm formation nuclear. Embryogeny irregular.

Fruit non-fleshy; dehiscent; a capsule. Capsules loculicidal. Seeds endospermic. Endosperm not oily. Seeds with starch (starchy). Cotyledons 2 (spathulate). Embryo achlorophyllous (1/1); straight. Testa red (rather fleshy). Micropyle zigzag, or not zigzag (?).

Seedling. Germination phanerocotylar.

Physiology, biochemistry. Not cyanogenic. Alkaloids absent (one species). Iridoids not detected (?). Proanthocyanidins present; cyanidin. Flavonols absent. Ellagic acid present. Saponins/sapogenins absent.

Geography, cytology. Neotropical. Sub-tropical to tropical. Tropical America and West Indies. X = 6–8.

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Malviflorae; Malvales. Cronquist’s Subclass Dilleniidae; Violales. APG (1998) Eudicot; core Eudicot; Rosid; Eurosid II. APG 3 (2009) Order: Malvales.

Species 4. Genera 1; only genus, Bixa.

Economic uses, etc. Orange dye for foodstuffs is obtained from the outer layer of the testa (annatto, arnotto, roucou).

Illustrations.
• Technical details: Bixa.
• Technical details: Bixa (Lindley).

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