A genus of about 6 species, trees, of warm temperate to cool temperate North America and Asia. The genus consists of 5 species – ours, 1 in w. North America, and 3 in Japan & Taiwan.
Ref: Farjon (1998); Farjon (2005); Michener (1993) In Flora of North America Editorial Committee (1993b); Mylecraine et al. (2004); Mylecraine et al. (2005); Mylecraine et al. (2009); Page In Kramer & Green (1990); Schulz, Knopf, & Stützel (2005). Show full citations.