Editing Betulaceae (section)

==Evolutionary history==
The Betulaceae are believed to have originated at the end of the [[Cretaceous]] period (about 70 million years ago) in [[Sichuan Province|central China]]. This region at the time would have had a [[Mediterranean climate]] due to the proximity of the [[Tethys Sea]], which covered parts of present-day [[Tibet]] and [[Xinjiang]] into the early [[Tertiary]] period. This point of origin is supported by the fact that all six genera and 52 species are native to this region, many of those being [[endemism|endemic]]. All six modern genera are believed to have diverged fully by the [[Oligocene]], with all genera in the family (with the exception of ''[[Ostryopsis]]'') having a [[fossil record]] stretching back at least 20 million years from the present.

According to [[molecular phylogeny]], the closest relatives of the Betulaceae are the [[Casuarinaceae]], or the she-oaks.<ref name="soltis2011">{{cite journal | vauthors = Soltis DE, Smith SA, Cellinese N, Wurdack KJ, Tank DC, Brockington SF, Refulio-Rodriguez NF, Walker JB, Moore MJ, Carlsward BS, Bell CD, Latvis M, Crawley S, Black C, Diouf D, Xi Z, Rushworth CA, Gitzendanner MA, Sytsma KJ, Qiu YL, Hilu KW, Davis CC, Sanderson MJ, Beaman RS, Olmstead RG, Judd WS, Donoghue MJ, Soltis PS | year = 2011 | title = Angiosperm phylogeny: 17 genes, 640 taxa | journal = [[American Journal of Botany|Am J Bot]] | volume = 98 | issue = 4 | pages = 704–730 | doi = 10.3732/ajb.1000404| pmid = 21613169 | s2cid = 8204080 | hdl = 2027.42/142064 | hdl-access = free }}</ref>