Picea purpurea Mast.

Picea purpurea is an important component of the subalpine conifer forests that dominate mountains in northern Sichuan, eastern Qinghai, and southern Gansu (Debreczy & Rácz 2011). It is a member of the P. likiangensis species complex and should be considered in that context.

Populations of affiliated spruces are distributed across western China, from Yulongxue Shan (or Lijiang Shan or Jade Dragon Snow Mountain) in Lijiang north to Gansu. On Yulongxue Shan itself and in adjacent areas of Lijiang and SW Sichuan we find Picea likiangensis sensu stricto: this is a relatively distinct taxon with somewhat glaucous leaves with stomata on all four surfaces, relatively sparsely set on, and radiating out from, stout, slightly hairy shoots; the seed cones are relatively large at 8–15 cm long. At the northern end of the range, in N Sichuan, SW Gansu and adjacent areas of Qinghai is P. purpurea: this is quite different from P. likiangensis, with shorter leaves densely set on and rather appressed to a more slender, densely hairy shoot, with dark green upper leaf surfaces often without stomata or one or two broken fine lines only; the seed cones are much smaller at 2.5–5.5 cm (Rushforth 2008; Debreczy & Rácz 2011). In between these two amply distinct entities lies ‘a vast area’ of variably intermediate populations (Rushforth 2008). Various names have been described from this in-between region; the spruce occurring there is here treated as P. likiangensis subsp. balfouriana (Balfour Spruce; q.v. for further discussion).

This is the spruce that Picea purpurea is most likely to be confused with and telling them apart can be tricky. When seed cones are available they are distinctive, being consistently smaller in P. purpurea than in Balfour Spruce. Few vegetative characters are diagnostic in and of themselves, but the shoots of P. purpurea are usually more densely hairy than those of Balfour Spruce, and the leaves are generally flatter, shorter and more densely set on the shoots. From his observations of wild trees Wilson also noted differences in aspect, with P. purpurea having ‘a thicker and more massive trunk, stouter and more wide-spreading branches and becomes flat-headed in mature individuals’ (Sargent 1916). Still these two spruces are frequently confused in collections, especially older trees for which records have been lost.

Masters described Picea purpurea in 1906 from specimens Wilson had collected in August 1903 (Wilson for Veitch 3026). Seed followed from Wilson’s 1910 expedition (W 4059, 4062, 4063, all gathered in western Sichuan) and the following year from Gansu under Purdom 815 (Sargent 1916) and again from Gansu in the 1920s, courtesy of Joseph Rock (Rock 12660, 12701, 12937, 12974, 13345, 13458 (Wagner 1992). Harry Smith made further collections from Sichuan in the early 1930s (Aldén 2006). At least in the UK and Ireland, Wilson’s introductions of 1910 made ‘much taller, more columnar trees’ than did Rock’s from Gansu (Rushforth 1987; it appears Purdom’s introduction resulted in few if any living plants).

Picea purpurea is a rare example of a spruce that appears equally at home in both continental and oceanic climate zones. Growth commences slowly on both sides of the Atlantic, but trees in Europe, and especially the UK, have grown larger than anywhere else. The tallest in the UK include trees to or just over 25 m at: Stanage, Powys; Eastnor Castle, Herefordshire; Westonbirt Arboretum, Gloucestershire; Dawyck, Scottish Borders; and Tatton Park, Cheshire. All these are likely Wilson trees. The tallest of all is at Stanage, 26 m tall × 62 cm dbh in 2023, while the Eastnor tree is almost as tall but has the largest girth, at 25.5 m × 74 cm dbh also in 2023 (Tree Register 2024). At the Arnold Arboretum in 1982 the tallest of four Wilson originals was 13.5 m but growing ‘in congested situations’ (Warren 1982); two of these remain and are now 38 and 31 cm dbh (Arnold Arboretum 2024). A fine tree in the Bergianska Trädgården, Stockholm, Sweden, planted c. 1930 and likely a Harry Smith collection, was 17.4 m × 31 cm in 2014 (Monumental Trees 2024).

There are few modern collections of this species noted in literature and on databases; its distribution is just a bit too far north to overlap with the majority of modern expeditions that prefer to focus on southern Sichuan and Yunnan. The Chinese Academy of Forestry distributed seed via Index Seminum on several occasions through the 1980s; material sent in at least 1980 and 1986 is established in several UK collections and appears genuine. Picea purpurea was collected under SICH 113 in 1988 but no living plants have been seen during the preparation of this account. Picea purpurea is occasionally offered for sale by specialist nurseries, but at least in the UK it often labelled P. likiangensis var. rubescens (pers. obs.).