Studies in Crataegus. XII. Cytological evidence for sexuality in some diploid and tetraploid species of North American hawthorns

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Abstract
Sexual development of the embryo sac has been demonstrated for five common (C. monogyna Jacq., C. punctata Jacq., C. mollis (T. & G.) Scheele, C. macrosperma Ashe, and C. calpodendron (Ehrh.) Medic.) and one rare (C. suborbiculata Sarg.) species of Crataegus (Rosaceae). These represent 6 of the 20 or so different Crataegus series in North America. All except C. suborbiculata (tetraploid) and C. macrosperma (tetraploid) are from diploid (2n = 34) accessions. Evidence from variation patterns known for the species discussed suggests that C. monogyna and C. punctata will be wholly or largely sexual outbreeders in North America; C. calpodendron will be mainly sexual; C. macrosperma will be a mix of agamospermic and sexual forms; and C. suborbiculata will be mainly apomictic. The bearing of this on North American Crataegus taxonomy is discussed.

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