Panarctic Flora

341203-04 The Trisetum spicatum aggregate T. molle, T. spicatum

Geography: Circumpolar-alpine (& Southern Hemisphere).

Notes: Aiken, Elven, Murray, and Tzvelev: All investigators agree that Trisetum spicatum s. lat. is polymorphic. It is a common species or species group throughout the Arctic, present in all major northern mountain ranges, and also in some tropical and Southern Hemisphere mountains (Borneo, Australia, New Zealand and the subantarctic islands, Hispaniola, South America). Two ploidy levels are well documented, tetraploid and hexaploid (e.g., Böcher 1959; Löve and Löve 1965, 1975a; Jonsell et al. 1975) but investigators disagree on whether there is a good correlation between ploidy levels and morphological features. Different views and approaches to this species or species group result in very different outcomes.

At one endpoint is the treatment of Randall and Hilu (1986). They studied T. spicatum s. lat. throughout its North American range and concluded that the data for 33 morphological characters revealed extreme variation within the species and did not support the recognition of more than one species or even of infraspecific taxa. Another endpoint is represented by Löve and Löve (1965) who accepted two species, the tetraploids as T. spicatum and the hexaploids as T. triflorum, each with two or more subspecies. The majority of investigators have landed somewhere between, e.g., Hultén (1959a) and Jonsell et al. (1975) who accepted one species but two or more subspecies.

Tzvelev (PAF proposal) accepted one species, T. spicatum, with 4-5 subspecies and one variety in the Arctic. For arctic Russia, Rebristaya (1964b) accepted two species - T. spicatum (s. str.) and T. molle - the latter with two subspecies: subsp. molle (implied for northeastern Asia) and subsp. alaskanum (in Kamtchatka and surroundings). For North America, Soreng et al. (2003) accepted two subspecies - subsp. spicatum and subsp. pilosiglume - and also Finot et al. (2004) accepted races. Rumely (2007) did not accept races for North America.

Aiken finds it difficult, from the conclusions of Randall and Hilu (1986), to propose a subspecific treatment. Elven considers that the morphological uniformity in the material from throughout the High Arctic and mainland Europe, where only tetraploids are found, contrasts with the polymorphy in the Beringian areas, western (Cordilleran) and low-arctic northeastern North America, southern Greenland, and Iceland, where both tetraploids and hexaploids occur. From a European viewpoint, he finds it difficult to accept that only one taxon is involved. The high-arctic and mainland European plant (T. spicatum s. str.) is characterized by, e.g., a dense spike-like inflorescence and a violet colour zone on the glumes and lemmas, whereas their margins are brown. The spikelets are comparatively small. The flowers considerably overtop the glumes. The awn is sharply geniculate and affixed at the upper 1/3-1/4 of the lemma. The culm is densely pubescent with long, soft, and (except at the very top) downward pointing hairs. Panicle branches are pubescent as well as the sheaths. The other plants differ in one or more of these features, especially in having a paler and looser panicle, distinctly larger spikelets where the flowers do not overtop the glumes considerably, and the awn is gently and evenly bent, not geniculate.

Elven: The variation does not fit well with our concept of races. The two major entities are largely sympatric. We have not seen any certain signs of transitions where they co-occur (observed in Iceland, Greenland, Canada, and Alaska). We rather see two distinctly different entities, probably reproductivelly isolated from each other. The appropriate rank for such situations is species. This opinion is, however, not shared by Aiken or by other American investigators of the group. The tentative treatment for the Checklist is as two species: T. spicatum and T. molle.