Description from Flora of China
Trees or shrubs. Young stems terete to frequently 4-angled or subalate, glabrous, puberulous, pubescent, or tomentose, often glabrescent. Leaves variably subopposite to subalternate or alternate, rarely opposite or truly alternate, subsessile or petiolate; stipules minute, caducous. Inflorescences terminal and axillary paniculate cymes. Flowers actinomorphic, campanulate to turbinate, flexibly 5-7-merous. Floral tube leathery, smooth walled with 6-12(-14) veins visible as dark lines, or with broad to narrow ribs or ridges; sepals narrowly to broadly deltate, sometimes subtended within by a narrow annulus; epicalyx segments alternating with sepals, small to prominent, or absent. Petals 6(-12), rose, purple, or white, crinkled, slenderly clawed. Stamens (6-)12-100+, inserted at or near base of floral tube, exserted, dimorphic in most species, 6 solitary in front of sepals with thick filaments and large anthers, 12-100+ in clusters in front of petals with thin filaments and small anthers, rarely monomorphic, then all filaments thin, subequal. Ovary globose to oblong, 3-6-loculed; style long-exserted; stigma capitate. Fruit dry, indurate capsules, surrounded at base by persistent floral tube, loculicidally dehiscent, 3-6-valved. Seeds numerous, obpyramidal, unilaterally winged from raphe; cotyledons rolled.
Lagerstroemia is in need of more extensive gatherings and study in order better to understand the extent of variability among and within the species.
The flowers are typically 6-merous, but can be 5-7-merous on the same plant. The floral tubes contract ± abruptly below the base of the ovary (campanulate) or taper gradually to the paired bracteoles of the pedicel (turbinate). The length of the floral tube is measured from the base of the ovary to the apex of the sepals; the pedicellate base (epipodium) extending from the base of the ovary to the bracteoles is not included.
A specimen of Lagerstroemia micrantha Merrill (J. Arnold Arbor. 21: 378. 1940, described from Vietnam) was reported by Furtado and Montien (Gard. Bull. Singapore 24: 276. 1969) from Taiwan (Faurie 8076, A) but without further information. One of us (Graham) saw this specimen, and another so named, at US from Hong Kong, but without collector or further data. Inclusion of L. micrantha in this Flora is deferred until the taxonomic status of the species is better understood.
In addition to the species mentioned below as being cultivated in China, the following have also been recorded as cultivated: Lagerstroemia siamica Gagnepain (native to Malaysia, Myanmar, and Thailand) in Taiwan (1950, no further data, A); L. reginae Roxburgh (native to India, Myanmar, and New Guinea) in Guangzhou (Hooker s.n., E); and L. floribunda var. brevifolia Craib (native to Cambodia and Thailand) without locality (Macartney s.n., BM).
About 55 species: tropical and subtropical Asia to Australia, north to Japan; 15 species (eight endemic) in China.
(Authors: Qin Haining (覃海宁); Shirley Graham)