Picea spinulosa (Griff.) Henry

As its vernacular name Sikkim Spruce might suggest, Picea spinulosa is distributed in the eastern Himalaya, in Sikkim and Arunachal Pradesh (as far east as the Mechuka valley) in northeast India, in Bhutan, and in the Yatung Valley of southeast Tibet (between Sikkim and Bhutan). Contrary to several reports it does not occur in eastern Nepal (Rushforth 2008).

The complex phytogeography of the eastern Himalaya and adjacent ranges has troubled modern botanists for nearly two centuries, and still many questions about the plants distributed here, their relationships and precise details of their distributions, remain unanswered. The spruces of this region have been well studied, but it is only in the relatively recent past that they have become better understood.

Picea spinulosa was the first spruce to be described from this region, by William Griffith in 1847, some ten years after he first encountered it on Bhutan’s Rudong La with the Pemberton Diplomatic Expedition of 1837–38 (Rushforth 2008). Sir Joseph Hooker would later encounter it in Sikkim’s Lachen Valley, in 1849, but it would not be introduced to cultivation until about 1878, from the Yatung or Chumbi Valley (the narrow part of Tibet that projects southward between Sikkim and Bhutan) (Elwes & Henry 1906–1913).

The early introductions tended to produce trees with rather long leaves, almost as long as those of Picea smithiana from the western Himalaya, already a familiar tree in British gardens by the time P. spinulosa arrived. Their distribution, at either end of the main Himalayan chain, together with their overall habit, similar cones, and the shared character of semi-pendulous branchlets, caused some botanists to consider them one and the same, and for a while Sikkim Spruce was treated as synonymous with P. smithiana following a treatment by Sir Joseph Hooker in the Flora of British India v. 653 (1888) (Elwes & Henry 1906–1913).

These days the West Himalayan and Sikkim Spruces are considered amply distinct (and can easily be distinguished by their leaves, a much richer, darker green, with more prominent stomatal banding beneath in Picea spinulosa). It has become much more likely for P. spinulosa to be confused with any of several spruces distributed to the east of its range, in southwest China and northern Myanmar. Here we find one of the major centres of diversity in this genus with many indigenous species, including several P. spinulosa relatives such as P. brachytyla, P. farreri and the P. likiangensis species group (Fu, Li & Mill 1999).

Keith Rushforth provides a useful overview of the distributions and points of distinction among these species in the 2007 International Dendrology Society Yearbook, and in the same paper rationalises the Picea likiangensis complex (Rushforth 2008). Rushforth notes the close affinity between P. spinulosa and P. brachytyla (sensu lato), but also the clear and consistent differences, notably the mature seed cones which remain glossy chestnut brown in P. spinulosa (cf. matt and less richly coloured in P. brachytyla), the leaves with stomatal bands and green margins and midrib beneath in P. spinulosa cf. two very broad bands obscuring the midrib beneath in P. brachytyla, and in the foliage arrangement, the leaves more or less spreading above the shoot in P. spinulosa, cf. strongly forward and pressed down along the upper surface of the shoot in P. brachytyla. The P. likiangensis species group differs in its seed cones, variably sized but always with thin, flexible, rhombic scales with free apices, cf. woody, firm, rounded scales in P. spinulosa. P. farreri could be confused with short-leaved forms of P. spinulosa but differs in its shoot texture, appearing as though puckered or wrinkled (Rushforth 2008; pers. obs.).

The original introductions of Picea spinulosa seem not to have been very long lived. The oldest Elwes & Henry could trace (with a confirmed planting date) were several at Castlewellan, Northern Ireland, raised from seed sent from the Calcutta Botanic Garden in 1890. In 1906 the largest was 6.7 m tall × 14 cm dbh in 1906; this tree produced cones for the first time the following year (Elwes & Henry 1906–1913). In 1966 the largest (though not necessarily the same) was 25 m × 92 cm; it blew down in 1976 (Tree Register 2024). The Castlewellan trees prompted Augustine Henry to make the combination Picea spinulosa – Griffith had originally published the epithet in the genus Pinus, at a time when the distinctiveness of Pinaceae genera was still poorly understood. Spinulosa means prickly, and it is generally assumed that Griffith applied this with reference to the prickly foliage, but this is hardly a unique character among spruces.

The tallest Sikkim Spruce recorded from the UK and Ireland was a tree that grew at Wakehust Place, Sussex; planted in 1916, it was 31 m × 68 cm dbh in 1981 and lost sometime later, perhaps in the great storm of 1987. The largest extant trees include examples 28 m × 81 cm in 2019 at Bicton Park, Devon; 27 m × 71 cm in 2024 at Parc Cefn Onn, Cardiff, and another of precisely the same dimensions in 2019 at Fota, Cork, from a 1914 planting (Tree Register 2024; Bean 1976). It is worth noting that this paragraph was compiled two days after Storm Darragh caused significant damage across the same areas where these trees are distributed, forcing one to wonder whether any of these ‘extant’ trees will soon be reported late and lamented.

An exceptionally beautiful group of three trees, planted by Jim Russell in Ray Wood at Castle Howard, North Yorkshire, demonstrate the fast growth rate of Picea spinulosa. Although in good soils and in a sheltered location, the best in 2019 was 24.6 m × 52 cm aged just 44 years (Tree Register 2024). These were supplied by the Hillier Nurseries, which is the most likely source of all the long-leaved Sikkim Spruces planted in Britain and Ireland through the middle decades of the 20th century (indeed, on the very rare occasions that specialist nurseries offer Sikkim Spruce today, it is the long-leaved form that prevails). Another of the same pedigree and vintage grows in quite different conditions at Bowood, Wiltshire, where it has made a handsome specimen tree in the pinetum, 19 m × 61 cm in 2016 and still vigourous, with a much fuller crown on account of its open position (Tree Register 2024; pers. obs. 2018 and see image below).

Picea spinulosa was probably introduced to North America in the late 19th century but, unsurprisingly, did not prove hardy here. Several attempts to grow it at the Arnold Arboretum in the early 20th century all met with failure (Arnold Arboretum 2024) and it does not feature in American textbooks such as Jacobson (1996) and Dirr (2009). Even mildly continental climates seem not to suit this species; it is not recorded from Hørsholm, Denmark, nor from Washington Park, Seattle, USA, which both have good spruce collections; a single plant is recorded from Belgium on the usually-thorough Beltrees database, 4 m × 25 cm dbh in 2002 at Hof ter Saksen, Beveren (Arboretum Wespelaar 2024). Even on the west coast of North America, where Sikkim Spruce ought to be hardy in favourable spots, only a single unconfirmed record was traced during research for this account, of a tree growing at the University of British Columbia Botanic Garden, Vancouver, wild-collected in India in 1984 (University of British Columbia 2024).

Much has been made up to now of the long-leaved (to c. 3 cm) forms of Picea spinulosa raised from early introductions from Sikkim, and perpetuated in cultivation through regular repropagation. The same form may occur in the Ha Valley of western Bhutan (K. Rushforth pers. comm. 2024). Most recent introductions, from the early 1980s onward, however, contrast sharply in their relatively short and more prickly leaves. Most are also yet to develop branchlets that nod to the same extent as in examples from Sikkim. Some of the more accessible examples grow on the Bhutanese Hillside at Benmore Botanic Garden (Argyll, UK) on poor, thin, acid soils in an area that experiences very heavy rainfall, rather cool summers and relatively mild winters (to c. –5°C). Collections here include Grierson & Long 1879 and 1885, Sinclair & Long 5697 and 5730, and NPSW 399. More extensively distributed are several Keith Rushforth collections, including KR 785, 1039, 1140, 1164, 1200, 1419, and 1608, all from Bhutan. Of these, KR 1419 is notable for coming from the type locality, while the further collections KR 3593 and 5986 are notable for coming from ‘the lower reaches of the Yarlung Tsangpo near the hamlet of Gyala’ at c. 2900 m asl in Tibet, where Sikkim Spruce comes incredibly close to P. linzhiensis, which occurs a few miles further up the valley at higher altitude (Rushforth 2008). At least one recent phylogenetic study has suggested that P. linzhiensis and P. spinulosa are sister species (Feng et al. 2018).