10 spp.) are disjunctly distributed among Europe, Asia, and North America, while Ostryopsis (3 spp.) is endemic to China.
Both morphological and molecular studies have generally recognized two major lineages in Betulaceae either as tribes Betuleae (Alnus and Betula) and Coryleae (Corylus, Ostryopsis, Carpinus, and Ostrya) (Jussieu, 1789; Prantl, 1894; Winkler, 1904; Melchior, 1964; Li & Skvortsov, 1999), or as subfamilies Betuloideae and Coryloideae (Spach, 1841; Regel, 1861, 1868; Koehne, 1893; Rendle, 1925; Rehder, 1940; Hutchinson, 1967, 1973; Dahlgren, 1975, 1980, 1983; Jury, 1978; Takhtajan, 1980; Thome, 1973, 1983; Furlow, 1990; Bousquet et al., 1992; Chen et al., 1999; Forest et al., 2005; Grimm & Renner, 2013).
The tepals of the pistillate flower are initiated from a common circular primordium at the base of the pistil in Cotylus, Ostryopsis, Carpinus, and Ostiya (Fig.
However, in Ostryopsis, Carpinus, and Ostrya both secondary and tertiary bracts are absent (Fig.
There are two major clades in the tree corresponding to Betuloideae (Alims and Betula', bootstrap support (BS) = 60%) and Coryloideae (Ostryopsis, Corylus, Carpinus, and Os try a: BS = 94%).