Plants forming very dense clumps. Rhizomes pachymorph, neck 5–11 cm. Culms 4–6 m, 1.5–2.5 cm in diam.; internodes 20–23 cm, cylindrical, smooth, white-powdery initially, becoming red-brown with exposure or yellow-brown, wall 3–6 mm thick, pith initially spongy; nodes with weakly prominent supra-nodal ridge; sheath scar prominent, yellow-brown setose, branches 9–25. Culm sheaths persistent, narrowly triangular, distally papery, brown to dark-brown setose, yellow-brown with dense purple-brown spots around each seta, longitudinal ribs prominent; auricles absent; oral setae few, erect, brown, deciduous; ligule ca. 1 mm, truncate, yellow-brown, tomentose, fimbriate to 1.5 cm; blade deciduous, linear-lanceolate, revolute, glabrous. Leaves 3–4 per ultimate branch; sheath shortly tomentose, external margin initially ciliate; auricles absent or very small; oral setae erect, white to grey-brown, papery, dense on distal sheaths, persistent; ligule truncate, ca. 0.5 mm, centrally shortly ciliate, laterally long-fimbriate to 1.5 cm especially on basal sheaths; blade lanceolate, 10–16 × 1–1.7 cm, base cuneate, white-grey tomentose abaxially and proximally adaxially, secondary veins 4-paired, transverse veins distinct. Synflorescence a racemose panicle, initially terminal to leafy shoot; spikelets 3–7, 2.5–4.3 cm; florets 3–7. Lemma densely white-grey-setose abaxially, margins ciliate. Palea 2-keeled, apically bifid, keels setose. Name from the Latin fungus, ‘mushroom or sponge’ referring to the well-developed spongy pith within the culm internodes.
Tall erect white oral setae on level or rounded leaf sheath shoulders make this easy to recognise.
Well adapted to the drier warmer climates of central Yunnan and California, B. fungosa has not thrived in N Europe. It is particularly intolerant of cold wet soil in winter as a young plant, and most of the original plants in the UK were lost, but the few that survived have eventually proven more resilient once established. The lush foliage with dense intermediate sized leaves is very attractive. Seedlings grown in California varied in leaf and culm size. Several had white variegation on the leaves, and these can be a stunning sight in a shady location. The culm colour also varied between seedlings, and some clones with a tendency to produce darker, chocolate brown culms have been selected.
Substantial differences have been noted between the description of Borinda fungosa by T.P. Yi and the plants cultivated under the name, as tabulated by Dr. J.-P. Demoly in Bull. “Bambou” de l’A.E.B.-n°hors série- 2006, including falcate leaf sheath auricles in the type, just as seen in the ‘internet species’... Comparison of bamboos in the type locality with those in cultivation would be very useful.
Borinda fungosa seed was collected in Yunnan by Prof. Xue Ji-Ru, the renowned bamboo taxonomist who worked closely with Prof. T.P. Yi, together describing many new species of bamboo. Seed was given by him to Karl Bareis for the US in 1989, and to Charlie Young in Holland.