Hydrangea robusta Hook.f. & Thomson

Most botanists and plantspeople accept that this is a distinct taxon at some level within the Hydrangea aspera complex. This does not mean that it is always clear which plants in gardens belong here. As a general guide, gardeners should expect under this name tall, robust shrubs with stout stems and thick, usually broad, leaves with fairly dense hair beneath, and rather long petioles. Lilac/pink/blue rather than white fertile flowers are the norm, and red-tinted petioles and veins are often seen. Some forms are potentially magnificent in a suitably large, semi-shaded position with adequate soil moisture, but hardiness varies.

The usual messy history of Hydrangea taxonomy has muddied the water more than necessary, perhaps. H. robusta was first described from Sikkim, at the western extreme of the aspera complex’s range (Hooker & Thomson 1857). The original Latin description highlights its thick branchlets and broadly ovate leaves, with stiff hairs above, tomentose beneath, and with long petioles; it is described not as a shrub but as ‘arbor parva’ (a small tree), implying at least erect habit and significant height. Once plants with similar long petioles were found in China, names proliferated: the most significant are H. longipes (first described from Sichuan – Franchet 1885), H. rosthornii (from what is now Chongqing – Diels 1900) and H. maximowiczii (from Guizhou – Léveillé 1903). As more specimens became available, Rehder (in Sargent 1913) felt able to sink H. maximowiczii in H. rosthornii, and he seems close to subsuming the latter into H. robusta. McClintock (1957) grouped all four in a single taxon, H. aspera subsp. robusta, but contemporary opinion is that this was a step too far. Flora of China (Wei & Bartholomew 2001), Plants of the World Online (Royal Botanic Gardens, Kew 2024) and the Chinese Plantplus website (Chinese Academy of Sciences 2024) all accept two long-petioled species, H. robusta and H. longipes. The key differences are the thicker textured leaves, more densely hairy beneath, with thicker petioles and stout, often more clearly 4-angled stems of H. robusta. While H. longipes normally has white fertile flowers and H. robusta pigmented ones, it seems clear that some H. robusta do have white ones. While intermediate examples occur (Sargent 1913), McClintock’s lumping has not been helpful to horticulture: it is far too easy to equate H. aspera subsp. robusta (a concept which includes H. longipes) with H. robusta, and so confuse what are in most cases straightforward species to distinguish. Adding to the confusion in gardens, H. ‘Snowcap’ (in the heteromalla complex) was distributed as H. robusta by Hillier Nurseries, UK, for many years (Edwards & Marshall 2019).

Garden introductions labelled H. robusta fall into four groups, those from Sikkim, those from Arunanchal Pradesh, plants from Sichuan and – more speculatively – Vietnamese material. Possible early Himalayan introductions are surrounded in uncertainty around identification; even if they persisted and were correctly named, it remained at best a very rare plant (Bean 1981; Aldridge 2025). Crûg Farm collections made on the Singalila Ridge, Sikkim (GWJ 9430 of 2002 and BSWJ 13900, 13999 of 2013) have now established a body of material from near the type locality, well matching the original description (Crûg Farm Plants 2024). These seem to need a mild, sheltered position to thrive. A specimen from GWJ 9430 at Trewithen, Cornwall, has grown well; it has bright red stems and petioles, very broad inflorescences in autumn, white sterile flowers with toothed sepals, and violet-blue fertile flowers. In colder Hampshire at the Sir Harold Hiller Gardens, a plant from BSWJ 13999 is regularly frosted to the base and does not flower (Aldridge 2025).

At least two collections from Arunachal Pradesh, NE India, seem to fit H. robusta, Dan Hinkley’s DH 16075 and Keith Rushforth’s KR 10735. They too have broad, open inflorescences and red young leaves and stems, the pigment persisting in the leaf veins and petioles. An example from KR 10735 at White House Farm, Kent, has less densely hairy leaf undersides than the Himalayan plants (pers. obs. 2023). Not yet widely tested, Hinkley’s collection thrives at his Windcliff garden in coastal Washington State. He enthuses ‘one of the most handsome Hydrangeas I have encountered, […] if I had room to plant only one Hydrangea, this would be it’ (Hinkley 2023).

At least two collections from around Baoxing, Sichuan seem to fit here; both have much less red in the stems and leaves. Maurice Foster’s MF 971055 of 1997 has proved hardy for him through cold winters in Kent, UK, in a north facing border with good overhead light (pers. comm. 2023). Flowering copiously from July, the inflorescences are not especially large, with pigmented fertile flowers, the sterile ones white with entire sepals. Roy Lancaster’s L 2021 of 1993 was germinated at Kew, a small number of seedlings being distributed. Two sent to Trelissick, Cornwall, were named ‘Blue Skies’ and ‘Pink Cloud’ (see under Hydrangea aspera Species Complex Cultivars). A third grows at Gresgarth Hall, Lancashire (Aldridge 2025).

Finally, plants which might well belong here have been introduced from northern Vietnam. WWJ 11888 of 2007 was placed here by Peter Wharton and Bleddyn Wynn-Jones, at least the latter having previously seen the species in the Himalaya. Seed was collected from very large shrubs, to 6 m tall, autumn flowering, with typical large, paddle-shaped, softly hairy leaves on long red petioles (Crûg Farm Plants 2024). Another Vietnamese find ‘Titania’, again with long red petioles and distinguished by immense sterile flowers, has also been tentatively placed here (see under Hydrangea aspera Species Complex Cultivars).

This is a promising species for wider garden use, but there is still much to learn.