Description from Flora of China
Rubus conduplicatus Duthie ex Hayata; R. incisus Thunberg var. conduplicatus (Duthie ex Hayata) Koidzumi; R. incisus var. formosanus (Cardot) Masamune; R. incisus subsp. koehneanus (Focke) Koidzumi; R. koehneanus Focke; R. koehneanus var. formosanus Cardot; R. retusipetalus Hayata.
Shrubs scandent, 0.5–2 m tall. Branchlets brown or dark purplish to purplish black, terete, slender, glabrous, with few prickles to 5 mm and glaucous bloom. Leaves simple; petiole 1–3(–4) cm, glabrous, with sparse, minute prickles; stipules lanceolate or linear, 7–9 mm, glabrous; blade ovate-lanceolate to oblong-lanceolate, 4–9 × 2–5 cm, papery, both surfaces glabrous, abaxially usually pale or whitish, base cordate, rarely subtruncate, margin 3-lobed or not, usually deeply 3-lobed on sterile branchlets, terminal lobe ovate-lanceolate, unevenly incised-serrate to doubly serrate, apex acuminate. Inflorescences terminal or axillary, flowers in clusters of 3 or in short few flowered racemes, 3–5 cm; bracts lanceolate or linear, 5–7 mm, glabrous. Pedicel 1–2.5 cm, glabrous. Flowers 1–1.7 cm in diam. Calyx cupular, abaxially glabrous; sepals triangular-ovate to lanceolate, 5–8 × 2.5–4 mm, apex acuminate to long caudate. Petals white, oblong or elliptic, rarely obovate, longer than sepals, both surfaces glabrous or slightly pubescent becoming glabrous, base clawed. Stamens many, shorter than petals; filaments broad, complanate. Pistils ca. 10–50, shorter than stamens; ovary glabrous. Aggregate fruit red at maturity, subglobose, ca. 1 cm in diam., glabrous; pyrenes rugose. Fl. Apr–May, fr. May–Jun.
Further study is required to determine the identity of Rubus glabricarpus W. C. Cheng var. eglandulosus Y. Gu & W. L. Li (Bull. Bot. Res., Harbin 20: 122. 2000), described from Yunnan, which might be synonymous with R. trianthus.
Mixed forests on slopes, forest margins, grassy slopes, roadsides, stream sides, montane valleys; 500--2800 m. Anhui, Fujian, Guizhou, Hubei, Hunan, Jiangsu, Jiangxi, Sichuan, Taiwan, Yunnan, Zhejiang [Vietnam].