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Rhizome neck 4-10 cm. Culms 2-5 m, 0.5-1.5 cm in diam.; internodes 12-20 cm, cylindrical, glabrous or initially slightly white-waxy, very smooth, initially dark green, streaked purple and purple-tinged above node, becoming burgundy-red after exposure to sun, then mid-brown; wall 1-4 mm thick; nodes unraised, very level; sheath scar very thin, white; branches 7-20, central dominant, red-brown. Culm sheaths slowly deciduous, papery, shorter than internodes, uniformly pale, distally with sparse very short light-yellow erect hairs, apically triangular to rounded; margins distally white-ciliate; auricles absent; oral setae absent; ligule 1-2 mm, truncate, serrate; blade lanceolate, reflexed, deciduous to persistent. Leaves 2-4 per ultimate branch; sheaths distally and veins red-purple where exposed, glabrous, external margin distally white-ciliate; auricles absent; oral setae absent; ligule ca. 1 mm, truncate to rounded, tomentose; external ligule shortly cilate; blade narrowly linear-lanceolate, delicate, matt bright green at first, 4-13 0.3-1 cm, glabrous, base rounded to cuneate, secondary veins 2-4-paired, margins very shortly spinescent, transverse veins not visible. Name Latin planatus ‘level’ referring to the smooth unraised culm nodes.
This bamboo from C Nepal differs from H. falconeri in its smaller narrow leaf blades, less striped, distally shortly pilose culm sheaths without mucus, and narrower culms with very level nodes. It has burgundy-red culms after exposure to sun, and leaf blades that often develop a blend of orange and red colours when chilled in the late summer. It is the hardiest Himalayacalamus known so far, the only species with foliage tolerating average winters in S England.
It was first grown at Kew in the 1970s, with incorrect information on its origin, as Arundinaria microphylla Munro, which is a small spreading Yushania species from Bhutan. Realising Arundinaria was the wrong genus as this bamboo forms clumps, and assuming the species name microphylla was correct, the next names used in western horticulture were Neomicrocalamus microphyllus and Drepanostachyum microphyllum. Neomicrocalamus species are unrelated scrambling bamboos from the tropical bamboo clade. Drepanostachyum microphyllum might appear a better guess but that species, from east of the Yangtse River in Chongqing, is actually a species of Ampelocalamus, with raised corky culm nodes to help it scramble up trees.
Thus despite having small leaves, this bamboo from Nepal is actually not any of the species published with the name microphylla/microphyllum/microphyllus. It is also not from Tibet, despite the cultivar name given to it, ‘Tibetan Princess’.
When found in Nepal in 1984 it was suspected to be a new species and described in 1991 with the unpublished name ‘H. aequatus’. However, it was tentatively included in similar species Himalayacalamus asper when that was formally described and named in 1994.
Only when Merlyn Edwards claimed the Kew plant as his own introduction, and Gib Cooper questioned the identity of his plants in Oregon was it realised that this species had been in cultivation in the west under misapplied names for more than 20 years. Discovery of the flowers of both bamboos confirmed that this bamboo and H. asper are indeed two distinct species, and this bamboo was removed from H. asper, and described as new species H. planatus in 2007, on the basis of its level nodes, pubescent rather than scabrous culm sheaths, and lack of leaf sheath auricles or leaf blade hairs.
 Himalayacalamus planatus was introduced into the UK from the Langtang Valley, C Nepal by Merlyn Edwards in Nov 1971.
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 "culm sheaths with short hairs at top")
 "margins with no cilia")
 "small leaves with short ligules")
 "purple ring above unraised node")
 "red culms from sun & cold")
 "old culms brown")
 "extra-vaginal branching")
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 "new shoots with no mucus")
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 "culm sheath interior glabrous")
 "foliage in summer")
 "autumn tints")
