Yersinochloa nianheana is morphologically most similar to Y. dalatensis and Y. nghiana, but Y. nianheana is distinguished from Y. dalatensis by culm nodes with a thick swollen patella (vs. without a thick swollen patella), culm-leaf blade erect (vs. reflexed) and auricles conspicuous (vs. absent). It also differs from Y. nghiana in culm-leaf blade flat at the base (vs. swollen at the base), palea with white cilia at the top (vs. glabrous), lodicules purple at ½ upper parts, unbifid at the base (vs. purple, bifid at base) and prophyllate bud 2-keeled (vs. prophyllate bud 1-keeled) (Fig. 3).

Figure 1. 

Yersinochloa nianheana V.T.Tran, N.V.Duy & T.V.Tran A habitat B clump C node D shoots E, F culm leaves G auricles H culm leaf I ligule J bud K leafy branch L, M section of a leafy branch N several branches with middle one dominant. Photos by Tran Thai Vinh from the type locality.

Figure 2. 

Yersinochloa nianheana V.T.Tran, N.V.Duy & T.V.Tran A, B, C inflorescence terminating at leafy branches D, E pseudo-spikelets F perfect florets G rachilla internode H prophyllate bud 2-keeled I glume J lemma K palea with rachilla extension L lodicules M stamens and pistil N anther apiece bearing tiny spines O young fruit P stigmas Q mature fruit. Photos by Tran Thai Vinh from the type locality.

Figure 3. 

Yersinochloa nianheana V.T.Tran, N.V.Duy & T.V.Tran, Y. dalatensis H.N.Nguyen & V.T.Tran and Yersinochloa nghiana V.T.Tran & T.V.Tran A1 bud A2 culm sheath A3 prophyll A4 lodicules B1 bud B2 culm sheath B3 prophyll B4 lodicules C1 bud C2 culm sheath C3 prophyll C4 lodicules. Photos by Tran Thai Vinh from the type locality.

Vietnam • Lam Dong Province, Duc Trong District, Voi Mountain, 1420 m a.s.l., 11°48'21.02"N, 108°24'46.12"E, 20 Sep 2023, N.V. Duy, V.T. Tran VTN 1990 (holotype DLU!; isotype VNMN!).

Culms and branches scrambling or hanging over nearby vegetation or trees, 5–8 m tall; internodes 50–70 cm long and 1.3–1.5 cm in diameter; white at the node when young, densely covered with adpressed white hairs; culm walls 0.4–0.5 mm thick; nodes with a thick swollen patella, hairy. Branches 5-7 with the middle one dominant and elongated. Culm leaves leathery purplish, sheaths with densely adpressed white hairs on the abaxial side; 25–27 cm long and 9–10 cm wide at the base, apex 6–7 cm wide; margins bearing dense white-brown hairs; blades cordate, slightly constriction at the base, erect, early deciduous, purple-brown, 14–18 × 3–4 cm, abaxial surface with dense white hairs at the base; auricles conspicuous, 1.0–1.2 × 0.1–0.2 cm; margins bearing dense white bristles, ca. 0.8–1.0 cm long; ligule short, ca. 1 mm, entire. Leafy branches bearing 8–10 leaves, foliage leaf blades wedge-shaped, 35–38 × 6–8 cm, acute or cuneate-obovoid at base, glabrous; veins 11–13 pairs; sheaths with ciliate margins, auricles with dense bristles 4–6 mm long; inner ligule with a low rim, ca. 1 mm; pseudo-petiole ca. 7–9 mm length, arching over. Inflorescences terminating at leafy branches, indeterminate; pseudo-spikelets typically 1.8–2.2 cm long, each subtended by a prophyllate bud, 2-keeled, with ciliate margins and hairy on 2-keels; 0.8–1.0 × 1.0–1.2 mm, apex acute, mucronate, ca. 0.5 mm long and consisting of one glume, one perfect floret. Rachilla internode below fertile floret ca. 0.1 cm. Fertile floret 1.0–1.2 × 0.2–0.4 cm; lemma oblong-lanceolate, 0.8–1.0 × 0.2–0.4 cm, veins 9–10, apex acute with 0.1 mm long, margins bearing dense white cilia; palea unkeeled, dorsal view showing rachilla extension and a rudimentary floret at apex, 1.0–1.2 × 0.5–0.6 cm, with margins bearing dense white cilia at the top, acute at apex, base inrolled; lodicules 3, lanceolate, purple gradually towards the top, ca. 0.3–0.4 × 0.1–0.2 mm, acute at apex, top with hairs 0.5 mm long, ciliate margins at ½ upper parts. Stamens 6; filaments free, 0.7–0.8 cm; anther ca. 5 mm, purple, apices bearing tiny spines, ca. 0.5 mm. Ovary green, glabrous with a long style, style oblique 1.0–1.2 cm; stigmas 3, purple; caryopsis oblique, with a relatively thin pericarp, 0.6–0.7 × 0.1–0.2 cm, with a long style, ca. 0.9–1.1 cm.

Yersinochloa nianheana grows in degraded natural forest in the valleys, between 1400 and 1500 m a.s.l., in Voi Mountain, Duc Trong District, Lam Dong Province.

The plants were found flowering in December 2023. New shoots from June to August.

Yersinochloa nianheana is of considerable importance to the local people. Its culms are used for making handicrafts and household tools.

The new species is named in honour of Prof. Xia Nianhe, for his contributions to bamboo research.

Yersinochloa nianheana is only known from a single population in Voi Mountain, Duc Trong District, Lam Dong Province, Vietnam. This population has no more than 500 mature clumps, all growing in degraded natural forests in valleys. According to IUCN Red List Categories and Criteria (IUCN 2022), the species is classified as data deficient (DD) and needs more surveys.