| # The Families of Angiosperms |

L. Watson and M.J. Dallwitz

### 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. The leaf lamina dorsiventral. Stomata mainly confined to one surface (abaxial); anomocytic. Hairs present; eglandular. Complex hairs present; tufted or peltate. Adaxial hypodermis absent. Lamina with secretory cavities, or without secretory cavities. Secretory cavities containing mucilage, or containing resin (with dark, refractive resinous contents); schizogenous. The mesophyll containing mucilage cells, or not containing mucilage cells; without sclerenchymatous idioblasts; containing crystals. The crystals druses (these abundant). Minor leaf veins without phloem transfer cells.

Axial (stem, wood) anatomy. Secretory cavities present (canals in the pith, and secretory cells in the cortex). Cork cambium present; initially superficial. Nodes tri-lacunar. Primary vascular tissues in a cylinder, without separate bundles; collateral. Internal phloem absent. Cortical bundles absent. Medullary bundles absent. Secondary thickening developing from a conventional cambial ring. Primary medullary rays narrow (broadening as they traverse the phloem).

The wood diffuse porous. The vessels small to medium; solitary, radially paired, and in radial multiples. The vessel end-walls horizontal to oblique; simple. The vessels without vestured pits; without spiral thickening. The axial xylem with fibre tracheids; without septate fibres. The fibres without spiral thickening. The parenchyma apotracheal (diffuse). The secondary phloem stratified into hard (fibrous) and soft (parenchymatous) zones. The wood partially storied.

Reproductive type, pollination. Unisexual flowers absent. Plants hermaphrodite.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’. The ultimate inflorescence units 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, phytochemistry. Not cyanogenic. Alkaloids absent (one species). Iridoids not detected (?). Saponins/sapogenins absent. Proanthocyanidins present; cyanidin. Flavonols absent. Ellagic acid present.

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 III core angiosperms; core eudicot; Superorder Rosanae; malvid. APG IV 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. • Le Maout and Decaisne: Bixa. • Le Maout and Decaisne: Bixa orellana: Lindley. • Bixa orellana: R. Wight (1840). • Bixa orellana: © Zoya Akulova (2016). • Bixa orellana, fruiting: © Zoya Akulova (2018).

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 8th June 2026. delta-intkey.com’.

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