Betula tianschanica Rupr.

Native to the dry mountains of central Asia, Betula tianschanica is very rare in cultivation, somewhat similar in appearance and behaviour to Betula microphylla, although also with some resemblance to B. pendula. In cultivation in Britain it forms a single-trunked tree but does not usually make an attractive specimen, due to late frost damage and winter dieback of twigs. The species was described in 1869 from specimens collected by von der Osten-Sacken near Lake Song Kol in Kyrgystan. At Wakehurst Place, Sussex, plants raised from seed collected in 1991 by Christopher Grey-Wilson from Almaty, Kazakhstan (just across the border with Kyrgystan) have developed good white trunks, and develop clear yellow autumnal colour (Grimshaw & Bayton 2009). RBG Edinburgh grows material collected in China by Sekerka, Bulánková and Skálová. In view of the species’ rarity, and the difficulty in identifying the tree, not all material found in arboreta should be assumed to be correctly named, unless the provenance is unimpeachable. The trademarked cultivar listed below was sourced from a research arboretum at the University of Minnesota, but the ultimate origin of the parent tree is not known. However, seed under the name B. tianschanica was introduced to the United States from Alma-Ata Botanic Garden, Kazakhstan in 1936, which is a likely candidate (United States Department of Agriculture 1941).

Throughout this region, tree birches occur as small isolated populations which have been given many names. Many are described as very rare (Eastwood, Lazkov & Newton 2009), and therefore of conservation significance, though no systematic study has been made of them. McAllister and Ashburner (2013) listed 21 little-known species that were accepted in Flora of the USSR (Kuzeneva 1936), most of which were placed by Skvortsov (in Vvedensky 1972) in synonymy with Betula tianschanica. Given how little is known of birch populations in this area, McAllister and Ashburner adopted a more conservative approach, citing no synonyms (the approach adopted here), but listing Kuzeneva’s species (see below) and noting that some of them might be synonymous with or intermediate between B. tianschanica, B. microphylla, or B. utilis subsp. occidentalis. Chromosome counts on several collections from the area have all been tetraploid, so these birches probably consist of a complex of isolated relict populations: during the Pleistocene (2.58 Ma–115,000 years BP) the climate in this region was moister during cold periods and the northern Betula-Picea forest extended south to join up with the forests of the Caucasus and the Pamir-Alai (Pakhomov 2006).

Betula alba var. schugnanica B. Fedtsch.
Betula kirghisorum Sawicz.
Betula saposhnikovii Sukaczev
Betula korshinskyi Litv., Trav.
Betula turkestanica Litv.
Betula pamirica Litv.
Betula alajica Litv.
Betula procurva Litv.
Betula schugnanica Litv.
Betula rezniczenkoana (Litv.) Schischk.
Betula jarmolenkoana Golosk.
Betula bucharica V. N. Vassil.
Betula hissarica V. N. Vassil.
Betula seravshanica V. N. Vassil.
Betula tadzhikistanica V. N. Vassil.
Betula pseudoalajica V. N. Vassil
Betula saposhnikovii subsp. jarmolenkoana (Golosk.) Ovcz., Czukav. & Shibkova
Betula dolicholepis Ovcz., Czukav. & Shibkova
Betula heptopotamica V. N. Vassil.
Betula. ferganensis V. N. Vassil.
Betula pyrolifolia V. N. Vassil.