Malus sylvestris (L.) Mill., Gard. Dict., ed. 8.: Malus n.° 1 (1768), nom. rej. (syn: Crataegus grata Salisb. ; Malus acerba Mérat ; Malus acerba var. barcinonensis Sennen ; Malus aprilovii Dimitrov ; Malus barcinonensis (Sennen) Sennen ; Malus bulgarica Dimitrov ; Malus communis subsp. acerba (Mérat) Bonnier & Layens ; Malus communis var. acerba (Mérat) Coss. & Germ. ; Malus communis var. glabra Coss. & Germ. ; Malus communis var. sylvestris (L.) Beck; Malus communis subsp. sylvestris (L.) Gams; Malus rhodopaea Dimitrov ; Malus sylvestris subsp. acerba (Mérat) Mansf. ; Malus sylvestris var. apetala L.H.Bailey ; Malus sylvestris var. aprilovii (Dimitrov) Ponomar. ; Malus sylvestris var. astracanica L.H.Bailey ; Malus sylvestris var. bulgarica (Dimitrov) Ponomar. ; Malus sylvestris var. glabra Holandre ; Malus sylvestris var. hortulana C.K.Schneid. ; Malus sylvestris var. microphylla Browicz ; Malus sylvestris var. rhodopaea (Dimitrov) Ponomar. ; Malus sylvestris var. sylvestris ; Malus sylvestris var. typica C.K.Schneid. ; Pyrus acerba (Mérat) Lej. ; Pyrus agriomelos Hoffmanns. & Link ; Pyrus malus acerba (Mérat) Asch. ; Pyrus malus var. acerba (Mérat) Coss. & Germ. ; Pyrus malus subsp. acerba (Mérat) Syme ; Pyrus malus proles acerba (Mérat) Rouy & E.G.Camus ; Pyrus malus f. barcinonensis (Sennen) A.Bolòs ; Pyrus malus var. glabra Neilr. ; Pyrus malus var. glabra W.D.J.Koch; Pyrus malus var. sylvestris L. ; Pyrus malus subsp. sylvestris (L.) Ehrh.; Pyrus pomum M.F.Fay & Christenh.; Pyrus sylvestris (L.) Gray);
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Europe to Türkiye: Albania, Austria, Baltic States, Belgium, Bulgaria, Central European Russia, Corse, Czechia-Slovakia, Denmark, East European Russia, Finland, France, Germany, Great Britain, Greece, Hungary, Ireland, Italy, Netherlands, North European Russia, Northwest European Russia, Norway, NW. Balkan Pen., Poland, Portugal, Romania, Sardegna, Sicilia, South European Russia, Spain, Sweden, Switzerland, Türkiye, Türkiye-in-Europe, Ukraine; Introduced into: Argentina South, Queensland as per POWO;
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here is some shots of Rosaceae plants from Warsaw
Smaller apples may be Malus pumila.
Please check Malus sylvestris Mill. ??
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References:
POWO
https://en.wikipedia.org/wiki/Malus_sylvestris
https://plants.ces.ncsu.edu/plants/malus-sylvestris/
https://www.treesandshrubsonline.org/articles/malus/malus-sylvestris/