The morphological intermediacy of Erigeron ×huelsenii (Asteraceae), a hybrid between E. acris and E. canadensis

Abstract

Morphological intermediacy is considered the first evidence of hybridization in many plant studies. However, morphologicalintermediacy does not always provide hybrid origin and can be a result of divergence. In this study, the authors revised the morphologicalintermediacy of Erigeron ×huelsenii, a putative hybrid between the Eurasian E. acris s. str. and North American E. canadensis, using thecharacter count procedure, a method that allows distinguishing hybridity from divergence. The measurements were made on herbariumspecimens, including 100 specimens of E. acris s. str., 100 specimens of E. canadensis, and 50 specimens of E. ×huelsenii, which werecollected in northeastern and southern Poland in 2013–2016. Among the 15 characters selected for the character count procedure, thehybrid showed intermediacy in 12 characters. The deviation was very significant (P < 0.05) and therefore the hypothesis of hybridity wasfully accepted. Moreover, details of indumentum and receptacle characters of the hybrid and its parental species were visualized usingscanning electron microscopy. The morphological characters of E. ×huelsenii presented in this study seem to be useful in the properidentification of all the hybrids between E. canadensis and E. acris s. l.