Picea likiangensis aggregate

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Picea likiangensis is one of those names that is still more likely to trigger off-putting thoughts of a bewildering diversity of lookalike trees than it is to imply a rather distinct conifer. It was described in 1899 based on specimens collected by Delavay in Yunnan, China. Over the years further taxa have been described that clearly have an affinity with P. likiangensis, but quite how many warrant formal recognition has never really been settled.

These populations of affiliated spruces are distributed in western China, from Yulongxue Shan (or Lijiang Shan or Jade Dragon Snow Mountain) in Lijiang north into Gansu province. At the one end, on the Yulongxue Shan and 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 8–12(–15) cm long. At the northern end of the range, in NW Sichuan and SW Gansu 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 populations lies ‘a vast area’ of variably intermediate populations (Rushforth 2008) and, in a scenario repeated endlessly throughout the plant kingdom, it is these intermediate entities that have given rise to so much confusion.

Various names have been described from this region, both at species and infraspecific rank, including Picea balfouriana, P. hirtella, P. likiangensis var. linzhiensis, P. likiangensis var. rubescens, and P. sikangensis. These have been employed in various ways by different authorities to define and characterise these populations, with some being placed in synonymy altogether, others being elevated to species rank or, more often, demoted to infraspecific rank.

In Pinaceae (Farjon 1990), the Flora of China (Fu, Li & Mill 1999), and Conifers Around the World (Debreczy & Rácz 2011) five varieties are recognised (the type var. likiangensis, and var. hirtella W.C.Cheng; var. montigena (Mast.) W.C.Cheng; var. rubescens Rehder & E.H.Wilson; var. linzhiensis W.C.Cheng & L.K.Fu).

Keith Rushforth revised this group of spruces in 2008 and significantly simplified matters. Finding var. linzhiensis sufficiently morphologically and geographically distinct from all other members of the group he elevated it to species rank as Picea linzhiensis (q.v.); regarding the remaining varieties, viz. var. hirtella, var. montigena and var. rubescens, Rushforth concluded that the characters on which these taxa were founded and maintained were ‘slight’ and he does not ‘consider them of sufficient botanical difference to justify more than one entity’ (Rushforth 2008). Rushforth concluded that the most appropriate way to treat this single entity was at the rank of subspecies; in this scenario, according to the rules of botanical nomenclature, the correct name becomes P. likiangensis subsp. balfouriana.

According to Rushforth (2008) then, this group (informally the ‘likiangensis group’) of spruces includes: P. likiangensis subsp. likiangensis, P. likiangensis subsp. balfouriana, P. linzhiensis and P. purpurea.

Farjon (2017) accepted P. linzhiensis at species rank but continued to follow his earlier use of variety for the other infraspecific taxa, and most collections tend still to follow Farjon in this regard. Be that as it may, Rushforth’s 2008 revision is a curious example of a habitual ‘splitter’ choosing instead to lump, and one might have thought this would cause more people to take notice. New Trees (Grimshaw & Bayton 2009) is the only major literary work to follow Rushforth’s 2008 revision, as we now do here, recognising Lijiang Spruce (P. likiangensis subsp. likiangensis) and Balfour Spruce (subsp. balfouriana) in addition to P. linzhiensis and P. purpurea. A key to these four spruces is presented below, adapted from New Trees with minor modifications.