Picea asperata aggregate

Articles in Group

• Picea asperata
• Picea crassifolia
• Picea koraiensis
• Picea meyeri

Picea asperata Mast. is the oldest name in a group of closely related spruces widely distributed across western and northern China, reaching extreme northeast China and adjacent parts of Russia and Korea. These spruces have in common various aspects of their morphology, notably: crown architecture; stiff, often stout shoots that are prominently ridged and grooved with well-developed pulvini (pegs); radially arranged, variably quadrangular leaves, often assurgent and/or directed forward on the shoot with stomata on all four surfaces; seed cones more or less cylindric, maturing fawn-brown. Another common thread is their ecology: they are all mountain taxa predominantly distributed in continental to cold-temperate climate zones with cool and relatively short growing seasons and long cold winters; precipitation is low to moderate, much of it falling as winter snow.

Masters described Picea asperata in 1906; in the same publication he also described P. aurantiaca and P. retroflexa, both of which have been considered by various authorities at various times to fall within the scope of P. asperata, either at infraspecific rank or in synonymy. Nakai described P. koraiensis in 1911. Two varieties of P. asperata were described by Rehder & Wilson in 1914, P. asperata var. notabilis and P. asperata var. ponderosa; at the same time they published P. meyeri and P. heterolepis (the latter treated by most authorities as a synonym of P. a. var. notabilis). In 1923 came P. crassifolia Kom. and in 1926 Picea pungsanensis Uyeki (this received little attention and was later reduced to a variety of P. koraiensis by Farjon). In 1986 a variety of P. meyeri was described, var. mongolica, later elevated to species rank as P. mongolica, but this has almost always been treated as a synonym of P. meyeri.

Although more research is needed to resolve this group Farjon (2017), Debreczy & Rácz (2011), and Fu, Li & Mill (1999) all agree that it includes at least four species – Picea asperata, P. crassifolia, P. meyeri and P. koraiensis – distributed in an arc from western Sichuan to where the borders of China, North Korea and Russia all meet. Neither their distinctiveness nor the justification of species rank seems to be in doubt among those authors, but it is worth stressing that the morphological differences are slight, all are rather vairable, and exhibit overlap in key characters with at least one other member of the group.

In some respects Picea asperata is the most distinct in its bark, breaking into large, rather thick irregular flakes from a young age (cf. rough but not flaking or detaching only in small thin flakes in the other species). Some accounts suggest it is further distinguished by its distinctly pungent leaves (spine-tipped, cf. obtuse or abruptly acute) but not all individuals of P. asperata have pungent needles, and young trees of the other species sometimes do. P. asperata is also the most commonly cultivated member of this group on both sides of the Atlantic. P. koraiensis is rarely cultivated, but is reasonably distinct in its finer, usually straight, usually green leaves, although it has been much confused with P. meyeri (and, historically, P. koyamae) (Farjon 2017).

Ostensibly these four species have discreet distributions, with Picea asperata occuring from western Sichuan to southeastern Shaanxi; P. crassifolia is largely distributed to the north of P. asperata in northeast Qinghai, Gansu, Ningxia and Nei Mongol; P. meyeri is largely to the east of P. crassifolia in Shaanxi, Shanxi, Hebei and Nei Mongol; and P. koraiensis is further east still, in Heilongjiang, Jilin, Liaoning and adjacent parts of Korea and the Russian Far East (Farjon 2017; Debreczy & Rácz 2011; Fu, Li & Mill 1999). In reality this neat southwest-to-northeast arrangement is not so clear cut. P. asperata and P. crassifolia have a wide area of overlap, and P. crassifolia and P. meyeri probably overlap to some extent in the far west of the latter’s range. Only P. koraiensis is truly disjunct (Farjon 2017; Debreczy & Rácz 2011; Fu, Li & Mill 1999), but collections from within its range exhibit considerable variation. The variability within these species, their slight differences (even when sampled from the core areas of their distribution) and the likelihood of introgression where ranges overlap, all conspire to make this group very difficult.

Things become more confusing and contentious when we consider the other aforementioned taxa, viz. Picea aurantiaca, P. retroflexa, Rehder & Wilson’s two varieties P. asperata var. notabilis and var. ponderosa (the dubious Mongolian Sand Spruce, P. meyeri var. mongolica or P. mongolica, is for simplicity discussed further under P. meyeri). These taxa were largely founded on minor differences in shoot and cone scale characters that appear trivial with the benefit of hindsight. In Europe, the widespread and much-studied P. abies exhibits variation similar to that which has given rise to this plethora of names in the orbit of P. asperata, but in the European case the maintenance of numerous infraspecific taxa has been consigned to history. Indeed, similar variation may be observed in other widespread spruces such as P. glauca in North America. As Farjon has observed: ‘population based studies [of P. abies] have revealed regional forms or ‘races’, some related to environmental factors, as well as much introgression…If such detailed studies were available for P. asperata [sensu lato], similar patterns would be likely’ (Farjon 2017).

In his Handbook of Conifers Farjon (2017) nevertheless errs on the side of caution and continues to treat var. notabilis and var. ponderosa, and P. aurantiaca and P. retroflexa .

The Flora of China account (Fu, Li & Mill 1999) treats P. asperata and two varities: var. notabilis (under the synonym var. heterolepis) and var. aurantiaca. Var. ponderosa is considered synonymous with the type, as is P. retroflexa.

In Conifers Around the World Debreczy & Rácz (2011) pay lip service to these taxa, noting, like Farjon, that the variability inherent in these names ‘is within the range typical for other Picea species’. They do not go so far as to lump them, but infer that if they are to be recognised they merit no more than varietal status under P. asperata (viz. var. aurantiaca, var. heterolepis, var. notabilis, var. ponderosa, var. retroflexa).

Several recent molecular phylogenetic studies have grouped Picea asperata, P. crassifolia, P. koraiensis, P. meyeri and P. retroflexa together in a clade that contains several other Asian species and the Eurasian P. obovata and European P. abies (Ran, Wei & Wang 2006; Lockwood et al. 2013; Sullivan et al. 2017; Feng et al. 2018; Shao et al. 2019). None of these studies sampled varieties of P. asperata and only Sullivan et al. sampled P. aurantiaca, which nested comfortably within the same clade. While all these studies agree that these seven species belong to the same clade, interpretations of the interspecific relationships vary widely based on the methods used.

In their phylogeny Lockwood et al. (2013) found Picea meyeri sister to the rest of the asperata group; Sullivan et al. (2017) also found P. meyeri well differentiated, but found P. aurantiaca sister to one of their P. meyeri samples, which seems unlikely, and neither study was able to resolve the relationships between the remaining taxa. Although working with a smaller sample, Feng et al. (2018) also found P. meyeri well differentiated, suggesting it is most closely related to P. crassifolia and P. koraiensis, which were placed as sisters to one another, as were the slightly more distantly placed P. asperata and P. retroflexa.

A more recent study employed a genotyping-by-sequencing technique to investigate the relationships of these taxa and their phytogeographical history (Liu et al. 2024). They concluded that ‘the Miocene uplift of the Daxinganling led to the differentiation of P. koraiensis’ and that ‘differentiation of [P. asperata, P. crassifolia and P. meyeri] was influenced by the uplift of both the Qinghai–Tibet Plateau and the Mongolian Plateau. The same authors found evidence that ‘frequent gene flow still occurs’ between these species (Liu et al. 2024). Others have highlighted late Pleistocene climate change and subsequent adaptations as a significant factor in the divergence of P. asperata and P. crassifolia (Bi et al. 2016; Feng et al. 2022).

Liu et al. (2024) concluded that Picea asperata and P. crassifolia are very closely related indeed and cluster together genetically, with P. retroflexa their next nearest relative. Shao et al. (2019) had similar results, but with P. crassifolia and P. retroflexa as sisters within a subclade that also included P. asperata. On the other hand Feng et al. (2022), using transcriptome-based analyses, found P. asperata and P. crassifolia well differentiated, but did not consider other species in the complex. P. mongolica clustered with P. meyeri for Liu et al. (2024), which can be interpreted to support the generally-held view that it does not merit distinction, especially not at species rank. Neither P. asperata infraspecifics nor P. aurantiaca were included by Liu et al., which could perhaps be criticised for its limited sampling of P. asperata, P. crassifolia and P. retroflexa (one population each) (Liu et al. 2024).

Clearly, further work is needed before a consensus may be reached. Taken in isolation, some of these studies could be used to justify revised taxonomies that merge several taxa in the complex, while others can be used to justify the status quo. Despite the considerable efforts that have been made in recent years we are not much closer to resolving the interspecific relationships in the Picea asperata aggregate, although the weight of evidence is beginning to point to there being more names than entities (a view expressed by others as early as the 1920s and 30s).

The implications for material in collections are complicated: in broad terms (i.e. at species rank) it is probably wise to maintain a familiar species concept across the complex, even if this means maintaining names for plants that can be difficult to distinguish morphologically. On the other hand, even with occasional modifications the existing taxonomies have done little in the last hundred years or so to reconcile the increasingly obvious imbalance between names and entities, and it could even be argued that a disproportionate taxonomy has contributed (until very recently) to a lack of serious scientific study and, more broadly, horticultural interest.

Partly because of their distribution and ecologies as wild plants these taxa are generally under-represented in western European cultivation. Species distributed in the Sino-Himalayan region are better suited to the climate of Atlantic Europe. In much of North America and central and eastern Europe the reverse is true; these spruces are well-suited to the prevailing continental climate whereas those distributed in climates influenced by the monsoon generally are not. Regardless of where and how often they are grown, plants belonging to the Picea asperata aggregate are often misidentified. The limited range of verified material available to study has hampered progress in our understanding of these taxa and their relationships – this situation is in direct contrast to the Picea likiangensis complex, for example, which Keith Rushforth revised in 2008, significantly simplifying a hitherto complex taxonomy that had largely gone unchallenged since the early 20th century. By studying historic literature and examining the characters on which P. asperata aggregate taxa were founded, and overlaying a modern understanding of the significance (or not) of those characters, it soon becomes clear that a similar simplification here is inevitable.

For Trees and Shrubs Online we will align with the major works of Farjon (2017), Debreczy & Rácz (2011) and Fu, Li & Mill (1999) in recognising Picea asperata, P. crassifolia, and P. meyeri in western and northern China, and P. koraiensis in northeastern China and adjacent parts of Korea and Russia, but we do not recognise any lower taxa.

Rehder & Wilson’s varieties in Picea asperata are increasingly difficult to justify and they are here considered synonymous with the type.

Picea aurantiaca has the most southerly distribution of this group but it has been omitted from nearly all recent phylogenetic studies. The same studies have included P. retroflexa but have failed to resolve its position. Descriptions in literature are inconsistent, and reveal sufficient overlap with P. asperata to justify sinking both of them within P. asperata.

An ecologically isolated population of Picea meyeri in Nei Mongol might possibly merit recognition as a variety, but only if consistent morphological differences can be proven (see P. meyeri taxonomic note).

Picea koraiensis var. pungsanensis is based on minor morphological differences that should be expected in any widespread spruce, and we do not treat it here.