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The families of flowering plants.                                                                                                                                                                

Begoniaceae C.A. Agardh.

                       

 

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Habit and leaf form. Herbs (mostly), or shrubs, or lianas. Plants succulent (mostly), or non-succulent. Perennial; with a basal aggregation of leaves, or with neither basal nor terminal 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. Leaves without a persistent basal meristem.

Leaf anatomy. Leaves 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).

Adaxial hypodermis commonly present (often of large cells, often of more than one layer). Cystoliths present (commonly), or absent. The mesophyll with sclerencymatous idioblasts, or without sclerenchymatous idioblasts. Minor leaf veins without phloem transfer cells (Begonia).

Stem anatomy. Cork cambium present; initially superficial. Nodes tri-lacunar, or penta-lacunar. Primary vascular tissue comprising a ring of bundles. Cortical bundles present (commonly), or absent. Medullary bundles present (commonly), or absent. Internal phloem absent. Secondary thickening developing from a conventional cambial ring. ‘Included’ phloem absent. Xylem with libriform fibres; with vessels. Vessel end-walls simple, or scalariform and simple. Pith with diaphragms, or without diaphragms.

Reproductive type, pollination. Fertile flowersfunctionally 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 unit 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.

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

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 3 core angiosperms; core eudicot; Superorder Rosanae; fabid; 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.

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