Betula utilis subsp. occidentalis Kitam.

Betula utilis subsp. occidentalis is a very white-barked subspecies found at the extreme western end of the Himalaya, where it forms forest up to the tree line. In overall appearance it is intermediate between subsp. jacquemontii and the central Asian B. tianshanica, with which it may intergrade where the taxa come into contact in the southern Tian Shan. Like subsp. jacquemontii it has bark peeling in large sheets, buds covered in white resin, and at least somewhat knobbly male catkins, while like B. tianshanica it has quite small, triangular-ovate leaves which are relatively thin, flat, with relatively few (5–7) pairs of weakly veined leaves with a tendency to double toothing and, in the extreme west, rough warty twigs with persistent white glands. Specimens intermediate between subsp. occidentalis and subsp. jacquemontii have not yet been found, but the area where they might occur has not been well collected and is currently difficult to access due to political instability and the presence of land mines. Many of the isolated birch populations from the mountains of central Asia have been described as separate species: they are discussed and listed under Betula tianshanica.

The range extends from the Karakoram Range in western Kashmir as far as west as Uzbekistan and the southern Tian Shan. From Kashmir eastwards, while still having the characteristic very white bark and white resin encrusted buds of Betula utilis subsp. occidentalis, the birches tend to have much larger, more oblong-ovate, deep green, glossy leaves and thicker twigs and are typical subsp. jacquemontii. (Two large-leaved collections from Sonamarg, Kashmir, referred by Ashburner & Schilling (1985) to subsp. occidentalis are closer to subsp. jacquemontii.) Some SABE collections of subsp. albosinensis from Hubei are in fact similar in general appearance, leaf size and shape to subsp. occidentalis, but differ in the colour of the bark.

The subspecies was described by Kitamura from plants collected in Nuristan, northeast Afghanistan (Ashburner & Schilling 1985). The smaller-leaved, fewer-veined Betula utilis subsp. occidentalis var. parva Kitam. was described by the same author from Karakoram, Puiju near ‘Baltso glacier’ [Baltoro glacier?] at 3300 m asl.

Maurice Foster’s introduction from northern Pakistan (MF (P) 2016) – reported to have been very white-barked in the wild – has not fared well in cultivation either at Wakehurst or in North Devon (Martyn Rix, in McAllister & Ashburner 2013), though it does grow reasonably well, albeit slowly, at Ness Botanic Garden. Surprisingly, collections from further northwest in Tajikistan, made by Géza Kósa and colleagues from Vacratot, the Hungarian national Botanic Garden, seem to be thriving and, judging by the photographs from the wild, promise to be most attractive.