Diploidy suggests hybrid origin and sexuality in Sorbus subgen. Tormaria from Thuringia, Central Germany

From Thuringia, Central Germany, seven presumably apomictic microspecies were described within Sorbus subgen. Tormaria (Sorbus aria × torminalis, S. latifolia group): Sorbus acutiloba, S. acutisecta, S. decipiens, S. heilingensis, S. isenacensis, S. multicrenata, and S. parumlobata. Flow cytometric ploidy estimation revealed one sample-standard ratio class for all taxa which corresponds to diploidy. As the apomixis in Sorbus is exclusive to polyploids we deduce that the sampled trees are F1 or early diploid hybrids of the combination S. aria × torminalis. The oldest name for this combination is Pyrus × decipiens Bechst. 1810 (= Sorbus × decipiens (Bechst.) Petz. & G. Kirchn.). Hence, the wide-spread presumption that the diploid hybrid Sorbus × decipiens is rare, sterile, and only scarcely found between its parents does not apply for Thuringia. Here, this taxon forms relatively dense stands and spreads by suckering and fertile seeds.