Hydrangea stylosa Hook.f. & Thomson

Oddly rare in Western gardens, Hydrangea stylosa is a pretty and apparently amenable species for a lightly shaded position, at least in milder, maritime areas such as Britain. It makes an open shrub to about 1.5 × 1.5 m. Some collections have purple-tinged leaves in summer (Kidd 2023). Flowering from June or July, the sterile flowers have strongly toothed white sepals; fertile flowers are pigmented, particularly attractive when blue (Foster 2023).

H. stylosa has often been compared to H. macrophylla, sometimes treated as a subspecies of it following McClintock (1957). Its leaves have something of the thickness of H. macrophylla and are essentially glabrous, but they are significantly narrower. The fertile flowers are distinctive, with strikingly reflexed petals, a largely inferior ovary, and the notably long styles which inspired the specific name. Molecular studies do not support an intimate relationship between the two; both De Smet et al. (2015) and Yang et al. (2024) place it in Section Stylosae.

This is a plant of the Eastern Himalaya, first described scientifically from Sikkim (Hooker & Thomson 1857), and extending east to Western Yunnan (Wei & Bartholomew 2001). Western collectors have sometimes suggested a much wider distribution in southern and western China (e.g. Foster 2023), but contemporary Chinese botanists seem to recognize it only from Yunnan and the Tibetan Autonomous Area, while accepting at least some short-styled plants as H. stylosa (Chinese Academy of Sciences 2024). Two other geographically separated taxa might be related. The much-debated Vietnamese H. indochinensis (at least, a plant identified as such, q.v.) seems to be a close relative (De Smet et al. 2015), and is often included within H. stylosa (Wei & Bartholomew 2001; Royal Botanic Gardens Kew 2024); horticulturally it is quite distinct, a rather tender evergreen. It also has narrower, lanceolate leaves (Merrill 1942). H. zhewanensis P.S.Tsu & X.P.Zhang is a narrow endemic from the border of Anhui and Zhejiang in eastern China. It differs in its oblong-ovoid capsule (versus subglobose), styles shorter, thicker styles (~1 mm in fruit versus 2–3 mm), and yellow (rather than blue) anthers (Wei & Bartholomew 2001). Maurice Foster’s Yunnan collection MF 93117 is currently listed by Crûg Farm as H. aff. zhewanensis (Crûg Farm Plants 2024); H. stylosa appears a better fit morphologically and geographically, although the upper leaf surface has long, sparse, spreading hairs (pers. obs. 2024; J. Aldridge pers. comm. 2024). Southern Chinese H. kwangsiensis is yet another taxon which has much in common with both H. stylosa and H. indochinensis; it has lanceolate leaves. Variation in this group is still far from properly understood; identifications of southern Chinese and Vietnamese plants are notably changeable and debatable.

H. stylosa seems to have entered cultivation as early as the 1850s under the synonym H. cyanema (Hooker 1858), collected by Thomas Booth in ‘Bhotan’ (N Assam, rather than present day Bhutan – Ludlow 1972) and sent to Thomas Nuttall, by then living in Lancashire, UK. By the mid 20th century Michael Haworth-Booth was unaware of it in cultivation (Haworth-Booth 1950); the final (1984) edition of his book ends with a short list of species ‘badly wanted’ for his collection, H. stylosa among them. Crûg Farm Plants offer a plant thought to be collected by Len Beer, who was active in the Himalaya around 1970 (Crûg Farm Plants 2024). More recent collections from Western Yunnan by Maurice Foster (MF 942115, W Yunnan), Dan Hinkley and others are occasionally grown in Britain (including Ventnor Botanic Garden, Isle of Wight – Kidd 2023), France (GardenBreizh 2024) and the Pacific Northwest .

To see this robust yet airy species is to love it. ‘Yet another little-known hydrangea with potentially high garden value’ (Foster 2023).