Plants forming dense to rather open clumps. Rhizomes pachymorph, neck 2--5 cm long. Culms to 3 m, to 1.5 cm in diam., nodding; internodes to 20 cm, terete, densely blue-grey waxy for first year, becoming yellow-green, longitudinal ridges very prominent, glabrous or distally lightly white-setose at first, cavity small, wall very thick; nodes prominent, supra-nodal ridge obscure, sheath scar prominent; branches initially (5)-7-(9), strong. Culm sheaths very persistent, much shorter than internodes, very tough, initially light green, distally purple-tinged, basally glabrous, most of sheath sparsely light brown setose at first, apex broad and sloping, longitudinal ribs obscure, becoming coloured, margins distally densely orange brown ciliate, external margin ciliate to base; auricles small and triangular on one side only; oral setae erect, short, sparse on taller side; ligule to 2 mm, obliquely truncate, serrate, finely ciliate, glabrous; blade narrowly triangular, glabrous, erect or reflexed, persistent. Leaves 3--5 per ultimate branch, mostly deciduous in winter; sheath glabrous, margins glabrous, often pink-purple; auricles absent; oral setae absent; ligule convex, to 2 mm, tomentose; external ligule shortly white-ciliate; blade lanceolate to broadly lanceolate, to 8 × 1 cm, fresh mid-green, base cuneate, glabrous, secondary veins 3-paired, margins spinescent-serrulate, transverse veins distinct. Synflorescence unknown. Name frigidorum Latin, ‘of cold places’.
Small thick-walled culms with most foliage leaves deciduous in winter, new leaf blades growing terminally from old sheaths in spring. Among the most hardy of all Borinda species introduced so far.
Nomenclatural note. Epithets frigidis, frigida, and frigidorum have all been used for this name. Yi used Fargesia frigidis, the ablative plural of the noun frigidum, meaning ‘Fargesia from cold regions’. He followed classical usage (e.g. Pliny, AD 79 in Nat. Hist. 19. 34, on garlic: in frigidis utilius uere seri quam autumno ‘in cold regions plant in spring not autumn’). Nouns used as epithets that are declined must be in the genitive declension (ICBN 2012), in this case plural: frigidorum. If a Group B adjective frigidis existed, then, like sylvestris or nepalensis, it could have been used to give adjectival epithets frigidis and frigide, but there is no such adjective, see the Oxford Latin Dictionary (‘Look Inside’ page 735). The Group A adjective frigidus has been used by most authors of botanical epithets, giving frigidus, frigida, and frigidum. However, Yi’s use of the noun frigidum rather than the adjective frigidus must be followed, giving Fargesia frigidorum and Borinda frigidorum, as in for example Valeriana frigidorum. For a broader explanation of the spelling of epithets see Nomenclature.
Borinda frigidorum was first introduced into the UK from Cang Shan, Dali, Yunnan, China, near the type locality, in 1995 (Stapleton 1056).