Description from Flora of China
Lagerstroemia subcostata Koehne var. glabra Koehne, Bot. Jahrb. Syst. 4: 20. 1883; L. stenopetala Chun.
Trees, small, 7-10 m tall. Branchlets 4-angled, glabrous. Petiole 2-5 mm; leaf blade ovate-elliptic or elliptic-lanceolate, 4.5-6.5(-11.5) × 2.2-3(-4) cm, papery, glabrous, lateral veins 5-7 pairs, base cuneate to subrounded, apex shortly to long acuminate. Panicles pyramidal, 5-12 cm. Floral tube (4 or)5 or 6-merous, 4-5 mm, smooth walled, with 12 dark veins or obscurely 12-ribbed; sepals 1.5-2 mm, adaxially glabrous; annulus present, thin, scarcely developed; epicalyx absent. Petals white, oblong-lanceolate to elliptic, 6-7 mm including claw 1.5-3 mm. Stamens ca. 20, dimorphic. Ovary glabrous. Capsules ellipsoidal, 6-8 × 4-5 mm. Seeds including wing ca. 6 mm. Fl. Jul, fr. Oct.
No consistent and taxonomically useful differences were found between Lagerstroemia stenopetala and L. glabra, although the lectotype of L. stenopetala was studied. The longer acuminate-caudate tip of the leaves of L. stenopetala seems to be the primary difference between the entities, and this condition can be found in some leaves of L. glabra. Given the variability of leaf shape generally found in Lagerstroemia, it is questionable whether this is significant at the species level. Petals of L. glabra and L. stenopetala are also similar and unusual for the genus, being lanceolate and not wrinkled in the proximal half. Furtado and Montien (Gard. Bull. Singapore 24: 185-334. 1969) also treated L. stenopetala as a synonym of L. glabra.
● Guangdong, Guangxi, Hubei.