Plants shrub-like to subarboreous, usually densely clumping; rhizomes pachymorph, necks similar in length, up to 30 cm. Culms in a single dense to loose clump (unicespitose), to 7 m tall and 3.5 cm in diam., erect or curving at base, apically nodding to pendulous; internodes to 50 cm, terete, usually finely ridged, without fine purple spots, usually blue-grey with light persistent wax, matt or becoming glossy, usually partially setose or pubescent, especially at top; nodes scarcely to moderately raised. Branches 3--7 per mid-culm node at first, above promontory, subequal, deflexed, or basally erect but arching out, lateral branch axes lacking subtending sheaths; buds at mid-culm lanceolate, with 2 often very tall, single-keeled bracts, open at front (closed at culm base), 3--9 initials visible within. Culm sheaths usually long-triangular, papery and deciduous (rarely oblong, thickened and persistent); blades long, reflexed, deciduous. Leaf sheaths usually persistent; blade usually matt, thin, venation distinctly tessellate, either persistent or deciduous in winter. Synflorescence ebracteate, semelauctant; branching paniculate, erect, never unilateral, usually long-exserted from narrow subtending sheath, often fasciculate in dense panicles. Spikelets several-flowered; glumes basally loose, and frequently subtending reduced non-viable buds. Stamens 3. Stigmas 3. Named after Norman L. Bor, forester and grass taxonomist of the Indian Forest Service and the Royal Botanic Gardens Kew.
Borinda is a temperate to subtropical genus that currently contains about 20 species, native to the Sino-Himalayan mountains from C Nepal to N Vietnam and W Sichuan. Many species have high local economic value and great horticultural potential. They are often indigenous to dwindling forest areas or individual mountain tops, and are thus potentially threatened with extinction as forests are cleared and climate change pushes species up the mountains.
Unlike Fargesia, the flowers are in panicles, never in tight racemes. The leaves are usually thinner, less glossy, and lighter green. The culms of Borinda are usually finely ridged, without spots, often scabrous or hairy, in contrast to culms of Fargesia. The culm sheaths are either longer and more triangular than Fargesia, or more thickened and persistent in species with very deciduous leaf blades. Similar to Yushania as well, but the rhizome necks are shorter and more consistent in length, producing single clumps and not running, and the leaf blades are arranged in a more regular fashion.
Borinda species are often included in a broad interpretation of Fargesia or more rarely Yushania. Early DNA analyses could not separate known and putative species of Borinda from those of Yushania well (see Fig 1, from Guo et al. 2001), or sometimes even from those of Fargesia (see Fig 2, from Guo & Li 2004). The latest results using ddRAD-seq data however have clearly shown that these genera correspond to 3 groups that are genetically distinct (Fig 3, adapted from Ye et al. 2019). Not only is it notable that Yushania and Borinda can be distinguished clearly from DNA. It is also important to appreciate that the distinction that was used to decide whether to place scores of new species in China in either Yushania or Fargesia, possession of short vs long rhizome necks, is obviously a clearer distinction than some might think. While Yushania and core Fargesia are demonstrably monophyletic, no analysis so far has resolved Borinda, as circumscribed by the morphological states above, as monophyletic rather than paraphyletic. However, this is also the case with many well-recognised bamboo genera, and other genera and groups in the plant and animal kingdoms. Evolution of a new genus or group, such as Yushania, often makes the genus it has evolved from paraphyletic. Over time only monophyletic groups remain after extinction of older members. Similarly only monophyletic genera may still be recognized after extinction of older taxonomists, who champion the recognition of paraphyletic genera.
Most of the species were described relatively recently, and nearly all were initially placed in Fargesia. China has many poorly-known species described in Fargesia that may or may not be Borinda. In the Flora of China all species of Borinda were included in Fargesia, largely to keep them all in the same place, rather than dividing them between Fargesia and Borinda. Many further species of Fargesia are likely to really be Borinda instead, but this cannot be proven without flowers, close examination of good collections of vegetative material/living plants, or DNA analysis, which has suggested a further 30 species for transferral into Borinda. There are several Chinese species currently in Fargesia that do not belong in either Fargesia or Borinda, nor in any published genus, so correct placement requires considerable care and further research.
The identification of a number of new Fargesia/Borinda introductions remains rather problematic, and may not be possible without more botanical fieldwork in China.
Large stature hardy clump-forming bamboos are the holy grail of bamboo horticulture. Hardy species in Fargesia and Thamnocalamus are rather small, while larger species such as those in Bambusa, Ampelocalamus, Drepanostachyum and Himalayacalamus are not sufficiently hardy. Therefore I was very excited to encounter a species in the snow in Bhutan in 1985, growing taller than the houses, and producing substantial culms from well-behaved clumps which, unlike like those of Phyllostachys or Yushania, will not spread widely. The genus Borinda was published in 1994, and from 1992 several species have been introduced to the west from Vietnam, Yunnan, Tibet, Nepal and Arunachal Pradesh.
One group of small, hardy Borinda species have very deciduous leaves in the coldest months. Although many bamboos shed a proportion of their leaves before winter, the routine annual fall of nearly all the leaf blades, as seen in these species, is unusual in the woody bamboos. Associated with thickened, more persistent sheaths and high altitude habitats up to 4000m, this would appear to be an adaptation to extreme cold and hence low water availability. The branching of such deciduous species is more erect, starting within the confines of very tough, persistent culm sheaths, and the internodes are consequently flattened to slightly sulcate above the branches. None of these species have auricles or oral setae on the leaf sheaths. Spikelets are dark and narrower, and their rhizome necks can be longer relative to culm size. B. emeryi from the Himalayas, and several Chinese species such as B. frigidorum and F. melanostachys seem to fall in this group.
Guo et al. (2001). Guo, Z.-H., Chen, Y.-Y., Li, D.-Z., and Yang, J.-B. 2001. Genetic variation and evolution of the alpine bamboos (Poaceae: Bambusoideae) using DNA sequence data. Journal of Plant Research 114: 315-322.
Guo & Li (2004). Guo, Z.-H., and Li, D.-Z. 2004. Phylogenetics of the Thamnocalamus group and its allies (Gramineae: Bambusoideae): inference from the sequences of GBSSI gene and ITS spacer. Molecular Phylogenetics and Evolution 30: 1-12.
Stapleton, C.M.A. (1998). New combinations in Borinda (Gramineae–Bambusoideae). Kew Bull. 53: 453–459.
Stapleton, C.M.A. (2000). New half-hardy bamboos from the Sino-Himalayan region. Amer. Bamboo Soc. Newsl. 21 (4): 16–21, with Bor biography
Stapleton, C.M.A. (2006). New taxa and combinations in cultivated bamboos (Poaceae: Bambusoideae). Sida 22(1): 331–332.
Ye, X.Y., Ma, P.F., Yang, G.Q., Guo, C., Zhang, Y.X., Chen, Y.M., Guo, Z.H. and Li, D.Z. (2019). Rapid diversification of alpine bamboos associated with the uplift of the Hengduan Mountains. Journal of Biogeography 2019; 00: 1– 12 https://doi.org/10.1111/jbi.13723