1. Begonia Linnaeus, Sp. Pl. 2: 1056. 1753.
秋海棠属 qiu hai tang shu
Perennial succulent herbs, rarely subshrubs. Stem erect, frequently rhizomatous, or plants tuberous and either acaulescent or shortly stemmed, rarely lianoid or climbing with adventitious roots, or stoloniferous. Leaves simple, rarely palmately compound, alternate or all basal; blade often oblique and asymmetric, rarely symmetric, margin often irregularly serrate and divided, occasionally entire, venation usually palmate; petiole long, weak; stipules membranous, usually deciduous. Flowers unisexual, plants monoecious, rarely dioecious, (1 or)2-4 to several, rarely numerous, in dichotomous cymes, sometimes in panicle, with pedicels and bracts. Staminate flower: tepals 2 or 4 and decussate, usually outer ones larger, inner ones smaller; stamens usually numerous; filaments free or connate at base; anthers 2-celled, apical or lateral; connectives extended at apex, sometimes apiculate. Pistillate flower: tepals 2-5(-10); pistil composed of 2-5(-7) carpels; ovary inferior, 1-3(-7)-loculed; placentae axile or parietal; styles 2 or 3(or more), free or fused at base, forked once or more; stigma turgid, spirally twisted-tortuous or U-shaped, capitate or reniform, setose-papillose. Capsule dry, sometimes berrylike, unequally or subequally 3-winged, rarely wingless and 3- or 4-horned; seeds very numerous, pale brown, oblong, minute, testa reticulate.
More than 1400 species: widely distributed in the tropical and subtropical regions of the world, with ca. 150 species in Africa, more than 600 species in Central and South America, and more than 600 species in Asia; 173 species (141 endemic) in China.
Begonia species in China are mostly distributed S of the Chang Jiang, particularly concentrated in SE Yunnan and SW Guangxi, with only a few extending into N China.
The authors learned of two additional, recently described species as this volume was going to press. Begonia guaniana H. Ma & H. Z. Li (Ann. Bot. Fenn. 43: 466. 2006) was described from NE Yunnan (Yanjin), where it grows on moist cliffs under bamboo forest at ca. 500 m. Its chromosome number is 2n = 24*. It resembles B. labordei, especially in its tuberous, stemless habit. Begonia coelocentroides Y. M. Shui & Z. D. Wei (Acta Phytotax. Sin. 45: 86. 2007) was described from W Yunnan (Yingjiang), where it grows on cliffs often in forests or near streams at ca. 1300 m, flowering in August and fruiting in October. It resembles B. oreodoxa in having parietal placentae at the upper part of the ovary, differing mainly in the female flowers with 5 tepals and the largest wing of the capsule being 20-22 mm and ligulate.
The records of Begonia balansana Gagnepain from Guangxi and Yunnan in FRPS (52(1): 212. 1999) are possibly errors and require confirmation. The second author has seen no specimens from China that would substantiate these records. This species is believed to be endemic to N Vietnam. See also Tebbitt (Edinburgh J. Bot. 60: 1-9. 2003).
It can be difficult to key out the sections of Begonia, because sectional distinctions rely heavily on the placentation structure, which is either unavailable on specimens or difficult to analyse (many Begonia specimens are poorly prepared). Information on sections to which Begonia species belong may be desirable to specialists, although it should be noted that there are disagreements about the placement of some species. Please refer to Y. M. Shui, C.-I Peng & C. Y. Wu, Synopsis of the Chinese species of Begonia (Begoniaceae), with a reappraisal of the sectional delimitation (Bot. Bull. Acad. Sin. 43: 313-327. 2002).
In China, all species are perennial herbs (rarely subshrubs). All species with basal tubers are described as deciduous, although living material is not available for all tuberous species. The aerial parts of the plants wilt in winter or in the dry season. Most species are monoecious with cymose, dichasial inflorescences. The inflorescences are usually protandrous (staminate flowers open before pistillate flowers) and gynaeandrous (staminate flowers basal and pistillate flowers distal).