Bonia Balansa is a small bamboo genus with five species and one variety endemic to South China except that B. tonkinensis Balansa is distributed in North Vietnam^[1–6]. Two species of Bonia, viz. B. saxatiis (L. C. Chia, H. L. Feng & Y. L. Yang) N. H. Xia and B. parvifloscula (W. T. Lin) N. H. Xia, are recorded from Guangdong Province ^{[2, 4]}.

In 2021, we conducted two bamboo surveys to Danxia Mountain and discovered three populations of an unknown Bonia species. This species resembles B. saxatilis in having white powdery internodes, and culm leaves with abaxially white-puberulent and brown-tomentose sheaths, developed auricles and similar blades, and the only difference is that the ligules of both culm and foliage leaves of the plants from Danxia Mountain do not possess long cilia on the margin. Therefore, we determined that the plants from Danxia Mountain should represent a new variety of B. saxatilis, which is described and illustrated below.

Besides, we also noticed that in the protologue^[7] of another newly described species from Danxia Mountain based on sterile material, namely Dendrocalamus pulverulentoides N. H. Xia, J. B. Ni, Y. H. Tong & Z. Y. Niu, some descriptions and photos (Fig. 3: F, G) of foliage leaves do not belong to this species, and the living collections of this species in South China Botanical Garden blossomed in October 2021. Thus, the emended description of foliage leaves (see the underlined content below) and supplementary description of floral morphology of this species were also provided.

Bonia saxatilis var. danxiaensis X. Li, J. B. Ni & Y. H. Tong, var. nov. (Fig. 1)

Type:   China. Guangdong Province: Shaoguan City, Renhua County, Danxia Mountain National Nature Reserve, near the top of Yuping Peak, 25°1ʹ 32″ N, 113°45ʹ30″ E, elev. 241 m, 20 April 2021, J. B. Ni et al. DXS037 (holotype: IBSC0884276, isotypes: IBSC0884277, IBSC0884278)

Diagnosis:   Bonia saxatilis var. danxiaensis differs from its nominate variety by having ligules of both culm and foliage leaves without long cilia on the margin, and can be distinguished from B. saxatilis var. solida (C. D. Chu & C. S. Chao) D. Z. Li by having ligules of both culm and foliage leaves without long cilia on the margin and culm leaves with abaxially white-puberulent and brown-tomentose sheaths.

Shrubby bamboos. Rhizomes pachymorph, shortnecked. Culms erect, sometimes scandent, 2–4 m tall, 3–7 mm in diameter; internodes terete, slightly swollen on infranodal region, 30–45 cm long, glabrous, whitepowdery, especially on infranodal region; pith spongy; nodes flat or slightly prominent, glabrous; supranodal ridge flat; intranodes 5–10 mm tall, glabrous; branches solitary, nearly as thick as culms, 0.5–1.5 m long; culm bud solitary, elliptic, pale yellow, puberulent abaxially, ciliolate on the upper margin, apex rounded. Culm leaf sheath persistent, thinly leathery, rigid, 1/5–2/5 as long as internodes, white-puberulent and brown-tomentose abaxially, sometimes glabrescent, margin densely brown ciliate, longitudinal ribs conspicuous; sheath scar with remains of sheath base; auricles oblong to falcate, amplexicaul, recurved, slightly unequal, 4–7 mm×1–2 mm; oral setae erect or slightly curved, radiating, 3–10 mm long; ligule serrate, ca. 0.5 mm tall, glabrous, apex truncate; blades lanceolate, usually erect, rarely reflexed, not amplexicaul, 3/10–1/2 as long as sheath, glabrous, base subcordate or slightly narrowed. Foliage leaves 9–13 per ultimate branch; sheath leathery, rigid, 7–9 cm long, white-puberulent and brown-tomentose abaxially, glabrescent when old, margins densely brown-ciliate, sometimes glabrous, thinly white-powdery, longitudinal ribs conspicuous; auricles elliptic to falcate, 1.5–3 mm×1–1.5 mm, easily deciduous when old; oral setae erect or curved, 1–7 mm long, usually deciduous when old; inner ligule 1–2 mm tall, glabrous or sometimes densely ciliolate on margin, apex truncate, serrate; outer ligule 1–2 mm tall, glabrous, sometimes ciliolate on the margin; blades lanceolate to oblong-lanceolate, papyraceous, 12.5–30 cm×1.5–4.5 cm, glabrous adaxially, sparsely puberulous along midveins abaxially, usually glabrescent when old, apex acute to attenuate, base truncate to slightly oblique, margin entire; secondary veins 6–10 pairs, transverse veins inconspicuous; petioles 2–4 mm long, glabrous. Inflorescence unknown.

Phenology:   New shoots from April to October.

Distribution and habitat:   This new variety is currently only found in the type locality, Danxia Mountain National Nature Reserve in Renhua County of Guangdong Province. It commonly grows on the shrubland or hillsides exposed to the sun at elevations of 200–300 m.

Etymology:   The epithet refers to the type locality, Danxia Mountain.

Chinese vernacular name: 丹霞单枝竹 (pinyin: dān xiá dān zhī zhú).

Additional specimens examined (paratypes):   CHINA. Guangdong Province, Shaoguan City, Renhua County, Danxia Mountain National Nature Reserve: near the top of Qianban Peak, 25°0ʹ37″ N, 113°43ʹ59″ E, elev. 254 m, 16 October 2021, J. B. Ni et al. DXS048 (IBSC); Shangtianlong, 25°0ʹ29″ N, 113°41ʹ 17″ E, elev. 301 m, 17 October 2021, J. B. Ni et al. DXS054 (IBSC).

Acknowledgments We also appreciate Zheng-yang Niu, Zhi-xian Zhang, Zhuo-yu Cai, Zhi-chu Li and the staff of Danxia Mountain Nature Reserve for their help during field trips.