A genus of about 45 species, shrubs and lianas, of e. North America and e. Asia. Molecular analyses have long suggested that Hydrangea as usually interpreted is polyphyletic (Soltis, Xiang, & Hufford 1995; Samain, Wanke, & Goetghebeur 2010) and should either be circumscribed more broadly to include other genera in tribe Hydrangeeae that are phylogenetically embedded (including, in our area, Decumaria), an approach that has been further developed and formalized by De Smet et al. (2015). Alternatively, Hydrangea s.l. could be separated into multiple, monophyletic segregate genera, an approach promoted by Ohba & Akiyama (2016). For now, we have followed the broad approach (with generic and sectional circumscriptions follow De Smet et al. 2015). If split, our species would end up in 4 genera: Hydrangea s.s. (arborescens, cinerea, radiata, and quercifolia), Decumaria barbara, Heteromalla paniculata, and Hortensia macrophylla. See Dirr (2004) and van Gelderen & van Gelderen (2004) for information on cultivated hydrangeas.
Ref: Boufford & Wood (1977); De Smet et al. (2015); Dirr (2004); Freeman (2016b) In Flora of North America Editorial Committee (2016); Hufford (2004) In Kubitzki et al. (2004); McClintock (1957); McGregor (2016b) In Flora of North America Editorial Committee (2016); Ohba & Akiyama (2016); Pilatowski (1982); Samain, Wanke, & Goetghebeur (2010); Soltis, Xiang, & Hufford (1995). Show full citations.