The World of Apples

Wild apples

Malus domestica (Suckow) Borkh.

Apple; Orchard apple

Description

The orchard apple is a tree of 2 to 10 m, sometimes 15 m. Its leaves are elliptic or ovate, usually 5–10 cm long, with bluntly toothed margins. The flowers are 3–4 cm across, rose in bud and opening white or sometimes pink, with 20 stamens and five styles. The fruit is green, yellow or red, plain, striped or blushed, and 2–5 cm across, occasionally 7 cm. Most trees have 34 chromosomes in their body cells, some 51 or 68. In North America it flowers in April and May and its fruit ripens from July to October1.

Because it is a complex of hybrid origin, a tidy description is hard to give. Woolly young shoots, leaves woolly beneath, a calyx that stays on the ripe fruit and a fruit indented at the base are the characters most cultivated apples share2. Trees grown from seed often bear small, bitter, sour fruit1.

Range and habitat

The apple is grown, and has gone wild, almost everywhere it is planted, in woods, thickets, hedgerows, roadsides, abandoned fields, riversides and shores2. In North America self-sown trees come from seeds spread by birds and mammals and from apples thrown away by people, and they grow from sea level to 1,600 m1. Plants of the World Online, which includes the Central Asian wild apple in the species, gives its native range as Afghanistan to Central Asia and Xinjiang, and lists it as introduced in Europe, the Americas, Australia and parts of Asia4.

Relationship to the wild species

The apple was first domesticated from the Central Asian wild apple, Malus sieversii. As it spread west it crossed with the European crab apple, Malus sylvestris, in both directions, so that today’s varieties are genetically closer to the crab apple than to their Central Asian ancestor. There was no genetic bottleneck at domestication, and cider apples and dessert apples do not form separate gene pools5. Most, but not all, cultivated apples also carry the crab apple’s chloroplast genome6. A 2017 genome study attributed about 46% of the cultivated apple’s genome to M. sieversii from Kazakhstan and 21% to M. sylvestris, with the origin of the remaining 33% uncertain. It also proposed that fruit size grew in two steps: once in the wild, before domestication, and again under cultivation7. In 2020 the authors of the first haplotype-resolved genomes concluded that the apple’s domestication was “mainly driven by interspecific hybridization”, finding about 23% of the Gala genome to be of hybrid origin8. The Caucasian crab apple seems to have contributed in Iran, and the Siberian crab apple has entered some modern varieties, partly through breeding for scab resistance2.

Because an apple seed gives a tree of unpredictable character, the traits of any variety are kept only by grafting9. Several thousand varieties have been recorded, yet the world’s production rests on a few dozen of them, grafted onto fewer than a dozen clonal rootstocks6.

The name

Linnaeus first named the orchard apple Pyrus malus, in 17533. Miller’s Malus pumila of 1768 is older than Malus domestica, which Borkhausen published in 1803 on the basis of Suckow’s Pyrus malus var. domestica of 178610. Miller seems to have meant M. pumila for the Paradise apple, a weak, dwarf form used as a rootstock that he took for a separate species2. One of the two neotypes later chosen for M. pumila is a cultivated M8 rootstock collected at East Malling in Kent in April 200010.

Borkhausen’s name was, strictly, superfluous and illegitimate1. A proposal of 2010 to conserve it1 was recommended by the Nomenclature Committee for Vascular Plants in 2017, “contradicting a previously published recommendation”11, and accepted by the Nomenclature Section of the International Botanical Congress at Shenzhen in July 20171. Malus domestica (Suckow) Borkh. is now a conserved name, and the names rejected in its favour include M. pumila and M. sylvestris. Under the code, a rejected name can be restored for a species that is kept separate from the conserved one, so Malus sylvestris remains available for the European crab apple10.

Where the sources disagree

  • Which name. The Flora of China (2003) uses Malus pumila for the cultivated apple12, and Cornille and colleagues judged M. pumila the more legitimate name in 2014 while using M. domestica, the more familiar one6. Since 2017 M. domestica has been conserved1,10. Some authors write the name Malus × domestica13.
  • What the name covers. Plants of the World Online includes the Central Asian wild apples in Malus domestica4, while Trees and Shrubs Online and most of the genetic literature use the name only for the orchard apple2. The 2022 revision of the genus left the cultivated apple out altogether, because of its complicated history14.
  • Hybrid or not. Barrie Juniper and David Mabberley argued that the orchard apple is simply the domesticated Central Asian wild apple, finding no evidence of hybridisation on its way west2; later genetic studies found a large contribution from the European crab apple5,7,8.
  • Domesticated or cloned. Cornille and colleagues see the cultivated apple’s clear genetic separation from its progenitor as “definitive evidence” that it is domesticated6. Spengler argues that the concept of domestication “falls apart” for large-fruited hybrid trees whose traits survive only through grafting9.

Varieties of this species in the atlas

Sources

  1. Malus domestica, Flora of North America vol. 9, Elizabeth E. Dickson, Flora of North America, eFloras.org. Supports: the description (trees 2–10(–15) m, leaves, flowers 30–40 mm, fruit 20–50(–70) mm, green, yellow or red, 2n = 34 (51, 68)); flowering April–May and fruiting July–October in North America; seedlings often bearing small, bitter, sour fruit; naturalised trees from seed spread by birds and mammals and from discarded apples; introduced habitats and range; Borkhausen's name "superfluous and illegitimate"; Qian and colleagues' 2010 proposal accepted at the Shenzhen congress in July 2017.
  2. Malus domestica, Julian Sutton and Nick Dunn, Trees and Shrubs Online (International Dendrology Society), 2021. Supports: shared characters after Bean (woolly young stems and leaf undersides, persistent calyx, fruit indented at base); naturalised almost wherever it is grown; Miller's M. pumila intended for the Paradise apple, a weak dwarf form used as a rootstock; involvement of M. orientalis in Iran and of M. baccata in East Asian apples; the view of Mabberley and colleagues (2001) that there was no evidence of hybridisation during the westward migration, and its rejection by later molecular studies; the name used only for the orchard apple in the horticultural and genetic literature; the common names apple and orchard apple.
  3. Malus Mill., Julian Sutton and Nick Dunn, Trees and Shrubs Online (International Dendrology Society), 2021. Supports: Linnaeus first named the orchard apple Pyrus malus in 1753.
  4. Malus domestica (Suckow) Borkh., Plants of the World Online, Royal Botanic Gardens, Kew. Supports: the accepted name and authority, nom. cons.; native range "Afghanistan to C. Asia and Xinjiang"; introduced across Europe, the Americas, Australia and parts of Asia; M. sieversii, M. niedzwetzkyana, M. chitralensis and M. pumila treated as synonyms.
  5. New Insight into the History of Domesticated Apple: Secondary Contribution of the European Wild Apple to the Genome of Cultivated Varieties, Amandine Cornille and others, PLoS Genetics 8(5): e1002703, 2012. Supports: domestication from M. sieversii with a major secondary contribution from M. sylvestris; bidirectional gene flow making the cultivated apple closer to M. sylvestris; no domestication bottleneck; cider and dessert apples not separate gene pools.
  6. The domestication and evolutionary ecology of apples, Amandine Cornille and others, Trends in Genetics 30(2): 57–65; Wageningen University repository, 2014. Supports: most but not all cultivars carrying the chloroplast genome of M. sylvestris; several thousand cultivars documented, but world production based on a few dozen cultivars on fewer than a dozen clonal rootstocks; clear differentiation from the wild progenitor as "definitive evidence" of domestication; M. pumila "more legitimate" under the rules, M. domestica more widely used.
  7. Genome re-sequencing reveals the history of apple and supports a two-stage model for fruit enlargement, Naibin Duan and others, Nature Communications 8: 249, 2017. Supports: 46% of the cultivated genome from M. sieversii in Kazakhstan, 21% from M. sylvestris, 33% of uncertain origin; the two-step model of fruit enlargement, before and during domestication.
  8. Phased diploid genome assemblies and pan-genomes provide insights into the genetic history of apple domestication, Xuepeng Sun and others, Nature Genetics 52: 1423–1432, 2020. Supports: domestication "mainly driven by interspecific hybridization"; about 23% of the Gala genome of hybrid origin; M. sieversii and M. sylvestris as the two major progenitors.
  9. Origins of the Apple: The Role of Megafaunal Mutualism in the Domestication of Malus and Rosaceous Trees, Robert N. Spengler, Frontiers in Plant Science 10: 617, 2019. Supports: a planted apple seed gives a tree of unpredictable character; hybrid traits maintained only by grafting and cloning; the argument that the concept of domestication "falls apart" for large-fruited hybrid trees.
  10. Madrid Code Appendices I–VII: Appendix IV, conserved and rejected names of species (Malus domestica), John H. Wiersema, Department of Botany, National Museum of Natural History, Smithsonian Institution. Supports: Malus domestica (Suckow) Borkh. (1803), based on Pyrus malus var. domestica Suckow (1786), conserved with a conserved type (Herb. Linnaeus No. 647.3); rejected names M. communis, M. pumila (1768), M. sylvestris, Pyrus praecox, Pyrus dioica, M. frutescens, M. paradisiaca and M. dasyphylla; one neotype of M. pumila a cultivated M8 rootstock collected at East Malling on 25 April 2000; a rejected heterotypic synonym restored when treated as a distinct species.
  11. Report of the Nomenclature Committee for Vascular Plants: 69, Wendy L. Applequist, Taxon 66(2) (abstract), 2017. Supports: the committee recommended conserving Malus domestica against M. pumila and six other synonyms, "contradicting a previously published recommendation".
  12. Malus pumila, Flora of China vol. 9, Gu Cuizhi and Stephen A. Spongberg, Flora of China, eFloras.org, 2003. Supports: the cultivated apple treated under the name Malus pumila, with M. domestica as a synonym; commonly cultivated in northern, north-western and south-western China.
  13. The genome of the domesticated apple (Malus × domestica Borkh.), Riccardo Velasco and others, Nature Genetics 42: 833–839 (abstract), 2010. Supports: the name written Malus × domestica.
  14. A revision of the genus Malus Mill. (Rosaceae), Jing-chao Li, Jian-quan Liu and Xin-fen Gao, European Journal of Taxonomy 853: 1–127, 2022. Supports: cultivated species such as M. domestica left out of the revision of the wild species "because of their complicated domestication history".