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Plants shrub-like, densely to loosely clumping; rhizomes pachymorph, necks to 25 cm. Culms unicespitose, pendulous, to 2–4 m tall, 1–2 cm thick; internodes terete, smooth, becoming yellow or red with exposure. Branches initially (3)-5-(7) per node, bud open at the front, sheaths dense and initially present between all branches. Culm sheaths slowly deciduous, blade usually erect. Leaf sheaths persistent, ligule ciliate, external ligule prominently ciliate, blade with evident tessellation of veins. Synflorescence a dense, contracted panicle or raceme, with occasional fasciculation and no pulvini; branches usually subtended by a substantial sheath or a ring of hairs. Pseudospikelets with 1 to several florets; glumes 2, more or less equal, longer than the adjacent lemmas, long-mucronate; lemmas 10-11-veined, long-mucronate; palea with several veins; anthers 3; ovary glabrous; style branches (2-)3. Name from the Greek thamnos, ‘shrub’, and kalamos, ‘reed’, referring to the habitat of the species.
Thamnocalamus is considered here to be a genus of about 6 species, distinct from closely related bamboos in the dense, complete branch sheathing on the (3)-5-(7) branches that develop in the first year, and the usually erect culm sheath blades. Culms can become light or deep red after exposure.
Like Arundinaria and Sinarundinaria, it was previously treated as a dumping ground for many unrelated species, all of which possessed compressed inflorescences of one kind or another. Analysis of the vegetative organs especially branching (Stapleton 1994), showed that many of the species belonged in other genera. Those without leaf vein tessellation (a chequered pattern) and more than 9 or so branches rather than 5 belong in Himalayacalamus. Those with 7 or more branches and fewer branch sheaths, as well as one-sided inflorescences like toothbrushes belong in Fargesia. The S African species T. tessellatus was also included in this genus (Soderstrom & Ellis 1982) largely on the basis of leaf anatomical characters until a better taxonomic location for it was found in Bergbambos, which is like Fargesia but has persistent leaf and culm sheaths giving a scruffy appearance, and lacks one-sided inflorescences. Like Fargesia species, those of Borinda also differ from Thamnocalamus in having 7 or more branches and fewer branch sheaths, but they also have open, rather than tightly compressed inflorescences with no bracts at points of branching.
The separation of Thamnocalamus from the genera Himalayacalamus, Fargesia, Borinda and Bergbambos, as suggested by inspection of vegetative characters especially branching, has been confirmed by analysis of their DNA. This has also distinguished Sri Lankan temperate species, which have similar branching, but have more open, ebracteate inflorescences, and are now placed in Karuna.
Thamnocalamus is now thought to be native only to the Himalayas, found from 2500-3700m. Hardiness varies, according to the altitude at which collected, tolerating down to about -5 to -15C. The distinctions between the species are not always clear-cut, with some overlap of features, probably as a result of hybridisation, and further fieldwork is required.
Three reasonably consistent species are widely distributed in the Himalayas. T. spathiflorus from Bhutan to E Nepal has hairy culm sheaths and prominent stout oral setae on leaf sheaths. T. nepalensis from C & W Nepal has glabrous culm sheaths and no leaf sheath oral setae. T. occidentalis from the W Himalayas (not yet in cultivation) has glabrous culm sheaths and prominent leaf sheath oral setae.
At the boundary between T. spathiflorus and T. nepalensis in C Nepal, and in the adjacent relatively low valleys of Kyirong & Nyalam Counties in Tibet, a rather variable group of plants known as T. crassinodus is encountered. Their culm sheaths may be hairy or glabrous, and leaf sheath oral setae are sparse or absent. In addition, culm nodes are prominently swollen, leaf blades are often small and numerous, and young culm internodes often have a dense blue-grey wax coating, the last two characters making them particularly attractive as cultivated plants. Thamnocalamus unispiculatus T.P. Yi & J.Y. Shi from Nyalam County appears to be conspecific with these, rather than T. nepalensis, which has also been collected in Nyalam County.
Attigala, L, Triplett, JK, Kathriarachchi, HS, Clark, LG. (2014). A new genus and a major temperate bamboo lineage of the Arundinarieae (Poaceae: Bambusoideae) from Sri Lanka based on a multi-locus plastid phylogeny. Phytotaxa 174 (4): 187-205.
Soderstrom, T.R., & Ellis, R.P. (1982). Taxonomic status of the endemic South African bamboo, Thamnocalamus tessellatus. Bothalia 14(1): 53–67.
Stapleton, C.M.A. (1994) The bamboos of Nepal and Bhutan, Part 2: Arundinaria, Thamnocalamus, Borinda, and Yushania. Edinburgh J. Bot. 51: 275–295.
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