Malus sieversii (Ledeb.) M. Roem.

Malus sieversii is the most celebrated wild apple of Central Asia, forming a major part of the fruit forests in the Tian Shan, as well as occurring in other forest types. It is threatened by habitat loss and degradation; fruit forest now exists only as remnants (IUCN 2020; Juniper & Mabberley 2019). It is the primary progenitor of the cultivated apple, M. domestica, and apparently also of M. asiatica.

M. sieversii was first described by Carl Ledebour (as a Pyrus) in 1830, from specimens collected in Khazakstan during 1793 by the short-lived Johann Sievers, a participant in an early Russian expedition to the mountains of Central Asia. Altogether a hairier plant than the European M. sylvestris, it forms part of a taxonomically difficult and incompletely understood complex. In particular, M. kirghisorum and M. turkmenorum (q.v.) are sometimes separated as distinct species; the extent of the geographical range of M. sieversii rather depends on the status of these forms. The line between wild and domesticated apples in Central Asia is not always clear cut.

Wild M. sieversii is remarkably diverse in horticulturally significant ways (Juniper & Mabberley 2019). Trees may be very spiny, or not at all. The flowers may be white, pink or rarely almost red (f. niedzwetzkiana, below). Fruits vary widely in size, colour, texture, flavour (including sweetness, bitterness, sourness but also more subtle elements – Baraniuk 2016), and in whether or not they are held on the tree into the winter. The apples are much harvested, very selectively, by local people. Aside from humans, bears and horses seem to be the main seed dispersers (Juniper & Mabberley 2019) although it seems possible that the evolution of large fruit was driven by megafauna which became extinct during the Pleistocene (Spengler 2019).

Wild M. sieversii populations probably contain genetic diversity which would be valuable in apple breeding, perhaps for disease resistance or tolerance of extreme environments. Many wild collections have been made for research and breeding purposes, initially mainly into Russian cultivation, more recently by Americans too (Forsline et al. 2003). When these collections leak out into wider cultivation, mainly in arboreta and botanic gardens, they tend to be labelled M. sieversii. Without knowing their provenance it would be impossible to say that they were not seedling M. domestica, some of which may anyway be essentially unhybridized, very lightly selected M. sieversii. Conversely, those who prefer to lump these wild apples into a broadly drawn M. domestica would so label them; the most detailed examination of records would be needed to discover which might be wild M. sieversii.

The UK and Irish champion (7 m × 103 cm, 2018) is one of a group of three planted in 1992 at the Yorkshire Arboretum, from a seed collection made in Uzbekistan (The Tree Register 2020; J. Grimshaw pers. comm. 2020). Another of similar age at Jodrell Bank, Cheshire was measured at 4 m × 38 cm in 2015 (The Tree Register 2020). Several specimens (Kazakhstan and Tajikistan provenance) are grown in behind-the-scenes areas at RBG Edinburgh (Royal Botanic Garden Edinburgh 2020).

In continental Europe, specimens are recorded at Gothenburg Botanic Garden, Sweden and Ghent University Botanical Garden, Belgium, from Kyrgistan and Kazakhstan respectively (Gothenburg Botanical Garden 2020; Plantcol 2020). In North America around 500 accessions of M. sieversii (taken here to include M. kirghisorum and M. turkmenorum) are grown at the US National Clonal Germplasm Repository, Geneva, NY (USDA/ARS, National Genetic Resources Program 2020). Relatively young, grafted specimens of some of these can be seen at the Arnold Arboretum, MA (Arnold Arboretum 2020).