The families of flowering plants

L. Watson and M.J. Dallwitz

Begoniaceae C.A. Agardh.

Habit and leaf form. Herbs (mostly), or shrubs, or lianas. Plants succulent (mostly), or non-succulent. Perennial; with a basal aggregation of leaves, or without conspicuous aggregations of leaves. Self supporting, or climbing; climbers root climbers. Mesophytic. Leaves small to medium-sized; alternate; spiral, or distichous; flat; ‘herbaceous’, or fleshy; petiolate; non-sheathing; simple (usually), or compound; when compound, palmate. Lamina entire (usually), or dissected; generally conspicuously asymmetric; often more or less trapezoid or ‘elephant’s ear’ shaped; sometimes palmatifid; palmately veined; cross-venulate. Leaves stipulate. Stipules intrapetiolar; free of one another; scaly, or leafy (often large); caducous, or persistent. Lamina margins entire, or crenate, or serrate. Leaf development not ‘graminaceous’.

Leaf anatomy. The leaf lamina dorsiventral (nearly always, the upper surfaces often exhibiting silvery areas representing air-filled spaces between epidermis and palisade). Leaves commonly with ‘pearl glands’ (these deciduous). Hydathodes present (occasionally), or absent. Stomata mainly confined to one surface (abaxial, often grouped); anisocytic, or paracytic, or diacytic, or cyclocytic (usually with 3–6 subsidiaries, these often in two rings). Hairs of diverse forms present (mostly multicellular, non-capitate and capitate, uniseriate and multiseriate, shaggy, etc.); nearly always eglandular (?). Adaxial hypodermis commonly present (often of large cells, often of more than one layer, sometimes on both leaf surfaces), or absent. Cystoliths present (commonly), or absent. The mesophyll with sclerenchymatous idioblasts (these sometimes crystalliferous), or without sclerenchymatous idioblasts; containing crystals. The crystals druses and solitary-prismatic. Minor leaf veins without phloem transfer cells (Begonia).

Axial (stem, wood) anatomy. Pith with diaphragms, or without diaphragms. Cork cambium present; initially superficial. Nodes tri-lacunar, or penta-lacunar. Primary vascular tissues comprising a ring of bundles (the bundles usually widely separated, but sometimes constituting an almost closed ring); collateral. Internal phloem absent. Cortical bundles present (commonly), or absent. Medullary bundles present (commonly), or absent. Secondary thickening developing from a conventional cambial ring (the resulting ground tissue of the wood composed chiefly of delicately septate prosenchymatous elements with simple pits). The axial xylem with vessels.

The vessels in radial rows, increasing in diameter towards the periphery of the stem. The vessel end-walls simple, or scalariform and simple. The axial xylem without fibre tracheids; with libriform fibres. ‘Included’ phloem absent. Tyloses present (occasionally seen), or absent.

Reproductive type, pollination. Fertile flowers functionally male and functionally female. Plants monoecious (the first inflorescence axes usually ending in male flowers, the last and sometimes the penultimate ones in females). Female flowers with staminodes, or without staminodes (androecium very small or lacking). Gynoecium of male flowers absent.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in cymes. The ultimate inflorescence units cymose. Inflorescences axillary (usually), or epiphyllous (two species); dichasia, with bostryx tendency. Flowers small, or medium-sized; somewhat irregular, or very irregular. The floral irregularity involving the perianth, or involving the androecium, or involving the perianth and involving the androecium. Flowers cyclic. Free hypanthium absent.

Perianth petaline; 2, or 4 (commonly), or 2–5, or 10 (rarely — Hillebrandia); free (usually), or joined; 1 whorled (in females and some males, then imbricate), or 2 whorled (in some males, then valvate); when 2, isomerous; more or less different in the two whorls (the outer members larger and covering the inner); white, or cream, or orange, or red, or pink. Corolla 2, or 4, or 5; 1 whorled, or 2 whorled; polypetalous (usually), or gamopetalous; imbricate, or valvate; unequal but not bilabiate.

Androecium (4–)50–100 (usually ‘many’). Androecial members branched, or unbranched; usually many and maturing centripetally; free of the perianth; free of one another, or coherent (connate); when joined, variously 1 adelphous; 2–5 whorled (‘usually many whorls’). Androecium exclusively of fertile stamens. Stamens (4–)50–100; diplostemonous to polystemonous. Anthers adnate; dehiscing via pores, or dehiscing via longitudinal slits; extrorse (usually), or latrorse; tetrasporangiate; appendaged (by the elongated connective), or unappendaged. Endothecium developing fibrous thickenings. Anther epidermis persistent. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral. 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 2–3(–6) carpelled (often longitudinally winged). Carpels isomerous with the perianth, or increased in number relative to the perianth. The pistil 2–3(–6) celled. Gynoecium syncarpous; synovarious; inferior. Ovary 2–3(–6) locular. Styles 2–3(–6); free (usually), or partially joined (at the base). Stigmas dry type; papillate; Group II type. Placentation axile. Ovules 15–50 per locule (‘many’); non-arillate; 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 pear-shaped. Endosperm formation nuclear. Embryogeny onagrad.

Fruit non-fleshy (usually), or fleshy; dehiscent (usually), or indehiscent; a capsule (usually, usually more or less winged), or a berry. Capsules usually loculicidal. Fruit 25–100 seeded (‘many’). Seeds non-endospermic; small. Embryo weakly differentiated to well differentiated (tiny). Cotyledons 2. Embryo straight.

Seedling. Germination phanerocotylar.

Physiology, phytochemistry. C3. C3 physiology recorded directly in Begonia. Not cyanogenic. Alkaloids absent (2 species). Iridoids not detected. Saponins/sapogenins present, or absent. Proanthocyanidins present, or absent; when present, cyanidin. Flavonols present, or absent; quercetin. Ellagic acid absent (5 Begonia species). Aluminium accumulation not found. Plants accumulating free oxalates.

Geography, cytology. Sub-tropical and tropical. Pantropical, concentrated in America. X = 10–21(+).

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Violiflorae; Violales. Cronquist’s Subclass Dilleniidae; Violales. APG III core angiosperms; core eudicot; Superorder Rosanae; fabid. APG IV Order Cucurbitales.

Species 920. Genera 3–5; Begonia, Hillebrandia, Symbegonia (Begoniella, Semibegoniella).

Economic uses, etc. Over 130 cultivated ornamental species of Begonia are commercially available.

Illustrations. • Le Maout and Decaisne: Begonia. • Le Maout and Decaisne: Begonia. • Begonia homonyma, as B. favargeri: Thonner. • Begonia carhcartii: Hooker’s Illustrations of Himalayan plants (1855). • Begonia hirtella: Bot. Reg. 1252, 1829. • Begonia adenopoda, as verticillata: Hook. Ic. Pl. 9 (1852). • Begonia heracleifolia: Bot. Reg. 1668, 1835. • Leaf hairs (Solereder, 1908).

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: 5th March 2018.’.