Description from Flora of China
Lagerstroemia subcostata var. hirtella Koehne; L. unguiculosa Koehne.
Trees or shrubs, to 14 m tall. Branchlets glabrous to gray puberulous or pubescent. Petiole 2-4 mm; leaf blade oblong, ovate-lanceolate, elliptic, obovate-elliptic, or infrequently obovate, 2-9(-11) × 1-5 cm, papery, abaxially glabrous or slightly pubescent, lateral veins 3-10 pairs, base broadly cuneate to subrounded, apex acuminate. Panicles pyramidal, 7-16(-30) cm, gray-brown pubescent, densely flowered. Floral tube 6-merous, 3.5-4.5 mm, with (10 or)12(or 14) dark veins or obscurely (10 or)12(or 14)-ribbed, glabrous to densely gray pubescent; sepals 1-2 mm, adaxially glabrous; annulus thin or apparently absent; epicalyx absent. Petals white, pink, or purple, broadly ovate with obtuse base, 7-10 mm including claw 3.5-6 mm, claw ca. as long as blade. Stamens 15-30, dimorphic. Ovary glabrous. Capsules globose to mostly oblong, 6-9(-11) mm, 3-6-valved. Seeds including wing ca. 4 mm. Fl. Jun-Aug, fr. Jul-Oct.
It is difficult to separate the following two species, Lagerstroemia glabra (including L. stenopetala) and L. caudata, from the widespread L. subcostata. Further knowledge about the degree of development of indumentum and variability of leaf shape and size is needed. More abundant gatherings may erase apparent differences between the species.
Forest margins, streamsides; low to medium elevations. Anhui, Fuian, Guangdong, Guangxi, Hunan, Hubei, Jiangsu, Jiangxi, Qinghai, Sichuan, Taiwan, Zhejiang [Japan, Philippines].