This is the common European hazel that is widely cultivated but rarely establishes from seed in North America, There are no records of naturalization in Ky., but the species is often planted as an ornamental, especilly the "corkscrew hazel" cultivar. Cultivation for nuts has generally failed, largely due to "eastern filbert blight", a native fungus that does not generally kill americana but "eventually kills most [avellana] hazelnuts grown in Kentucky"; also "the European hazelnuts often have their flowers killed during the winter in Kentucky" (Masabni et al. 2007). Cross-pollination is generally needed for nut production, and the timing of pollen release may be offset by a few days from emergence of receptive stigmas on the same plant. Moreover, different clones appear to have different timings, resulting in "heterodichogamy" (Renner 2001). It is likely that similar variation occurs in americana, but there has been no published assessment of dichogamy in that species. C. avellana differs from americana as follows (FNA 3): involucre shorter than to only slightly longer than fruit (versus slightly longer to twice as long); nuts mostly 15-20 mm long (versus 10-15 mm); staminate catkins mostly in groups of 2-4 (versus 1-2), peduncles more than 5 mm broad (versus 5 mm or less); large shrub or small tree up to 3-8 m tall (versus shrub 2-5 m). Verified chromosome numbers in the genus and this species are generally 2n = 22, but there is one report of 2n = 44 from avellana (tropicos.org/Project/IPCN). Reports of 2n = 28 (e.g. FNA 3) are probably erroneous in general (Oginuma et al. 1999). Hybrids of avellana and americana have been produced, and considerable resistance to the blight has been developed in breeding programs (e.g. Revord et al. 2020).