Graminoid forb growing in compact tussocks, with branching both inside (intravaginal) and outside leaf sheaths (extravaginal) but with no horizontal rhizome branches (in Svalbard plants). Aerial shoots erect from tussock. Base of aerial shoots surrounded by firm, dark straw yellow coloured sheaths of marcescent leaf bases, surviving for several years and contributing to the tough structure of the tussocks. Culms 20—30 cm, erect, moderately stout (0.6—0.8 mm broad beneath the panicle), glabrous, smooth or sparsely scabrous just beneath the panicle.

Leaves flat, pale bluish green due to small papillae, with 13–17 veins, veins on the lower surface distinct and glabrous, on the upper surface raised as sharp ribs and densely pubescent with short stiff hairs, mid vein similar to other veins, leaf margins minutely but densely scabrous. Basal leaves 10–12(15) cm long, 2.5–3.5 mm broad. Culm leaves 1–2, not decreasing much in length upwards on culm, flag leaf blade 3–4 cm long, attached below middle of culm. Ligula 2–4 mm, lacerate.

The units of the inflorescence of Poaceae are the spikelets, nearly always numerous in a panicle or spike-like inflorescence. Spikelets are composed of 2 glumes (bracts for the spikelet) and one or more flowers (the term used below) or rather floral units, often named ‘florets’ because we do not know what is the exact flower. A flower or floret is composed of a lemma with one mid vein (probably the floral bract), a palea with 2 mid veins (either fused bracteoles or perhaps 2 fused perianth leaves), 3 small organs called ‘lodiculae’ and essential in the opening of the flower at anthesis (possibly transformed perianth leaves or transformed stamens), 3 stamens (mostly), and a gynoecium of 2 fused carpels with 2 feathery stigmas and one seed.

Inflorescence a dense, cylindrical panicle, rarely interrupted at base, 3—5 × 1 cm, occupying 1/3—1/5 of culm length with ascending branches. Panicle not increasing significantly in width during anthesis, strongly tinged in lilac or pale purple, with numerous nodes and with 3—5 branches at each of the lower nodes. Branches 10—15 mm long, densely scabrous with short stiff hairs, longest branches with 3—5 spikelets along most of their length. Spikelets 5—7 × 0.9—1.2 mm, very narrowly lanceolate in outline, one-flowered. Bracts (glumes and lemmas) with rounded backs. Glumes 5—7 mm, more or less equal in length, as long as spikelet, narrowly lanceolate, acuminate, with a marked mid vein and two indistinct lateral veins, scabrous on mid vein, smooth or sometimes scabrous on surface beside mid vein, dull lilac with a narrow, white hyaline margin. Lemma hidden by glumes and slightly shorter, 4—6 mm, narrowly lanceolate, acute or with 2—3 teeth at apex, with the same coloration as the glumes but with a much broader, white hyaline apex through which the three strong, dark violet veins run into the teeth. A long, stout, geniculate awn 5—7 mm is attached at the lower 1/3 of the mid vein and protrudes far beyond the spikelet. Callus hairs at the base of the lemma short, less than 1/2 as long as the lemma. Palea about as long as lemma or shorter, with 2 veins. Anthers 1.3—1.6 mm, shrivelled (non-functional; in Svalbard plants).

Fruit an achene with one seed.

Asexual reproduction by seeds (agamospermy); no vegetative reproduction. Fruit set is probably quite regular. The culms and panicles are retained for several years, some also with unripe fruits with lemmas (with awns). However, in general only the glumes are retained and the mature fruits shed and spread.

Fruits (inside florets) are adapted to dispersal by wind and animals due to the long awn of the lemma.

The callus hairs at the base of the lemma is a diagnostic character for the genus Calamagrostis compared with other grass genera. The only other species of Calamagrostis in Svalbard, C. neglecta ssp. groenlandica, differs in very many aspects and will never be mistaken for C. purpurascens. It has loose tussocks or mats with filiform to very narrow, green (not bluish green and papillose) leaves, bases of shoots covered by a loose, slim, pale brown sheath of marcescent leaf remains, more slender culms, and a narrow, dark violet or purple panicle where awns are not protruding. It also grows in a very different type of sites: shallow mires, marshes and wet sediment flats.

No other grass in Svalbard resembles C. purpurascens closely.

Calamagrostis purpurascens occurs in small gaps in the vegetation carpet, primarily in arctic steppe vegetation. The growth sites are dry in all seasons, with soils with a very basic reaction. In the arctic steppes, the rain and snow is very limited, and the evaporation causes an upward current of water rich in minerals, which evaporates and leaves the minerals at the surface. The growth sites in Wijdefjorden are also exposed to strong winds; especially fall winds through the valleys from a large ice cap to the east. The wind is persistent and regularly carries silt and sand from the glacier fronts, sometimes to an extent that reduces visibility. The very tough tussocks of Calamagrostis purpurascens are able to sustain these winds and sedimentation and also the snow and ice drift in winter storms.

Thermophilous. The occurrences are all situated in the middle arctic tundra zone and the clearly continental sector, within an area of 6 km (W—E) × 14 km (S—N), within the largest area of arctic steppe in Svalbard. The species is known from four valleys on the east side of inner and middle Wijdefjorden (Ny-Friesland) on N Spitsbergen: Smutsdalen, Reinsbukkdalen, Flatøyrdalen and Ringhorndalen. In Smutsdalen some tens of tussocks were recorded (Elvebakk & Nilsson 2002), in Reinsbukkdalen one population with 200—300 tussocks (Elvebakk & Nilsen 2002), in Flatøyrdalen two populations with ca. 80 and 30 tussocks (I.G. Alsos, R. Elven, A.K. Brysting, P.B. Eidesen observ. 2010), and in Ringhorndalen two populations with together less than 50 tussocks (I.G. Alsos & A.K. Brysting observ. 2010).

Calamagrostis purpurascens is a common species in many parts of the Arctic, especially in Greenland, N North America and Beringia, but also reaches westwards in Siberia to the Khatanga area just east of Taimyr. The gap in this distribution between Greenland and Taimyr is huge and includes the North Atlantic. The finds in Svalbard closed a significant part of this gap (ca. 25 %). The closest dispersal connection of the Svalbard plants is westwards to N Greenland.

Calamagrostis purpurascens is a polymorphic and ploidally variable species with reported chromosome numbers and ploidy levels from tetraploid (4x, 2n = 28) to dodecaploid (12x, 2n = 84). The chromosome number of the Svalbard plants is not known but the plants in arctic Canada, Greenland and N Siberia are hexaploid and octoploid (2n = 42, 56; see Elven et al. 2011).

The genus Calamagrostis is probably hybridogeneous (N.N. Tzvelev pers. comm.). The lowest chromosome number known in the genus is tetraploid. There is a distinct pattern in the genus when it comes to reproductive system. All N European tetraploid species are sexual, whereas all species or population groups with a higher number have asexual seed production (agamospermy). There is no vivipary (bulbils) in this genus. The higher polyploids may partly have arisen within a species (autopolyploidy, as suspected for C. purpurascens and C. epigejos), and partly as hybrids between species (as shown for C. phragmitoides and suspected for C. lapponica). A huge, early cytological work has been performed on this genus, especially by A. Nygren documenting the agamospermy and some of the hybrid combinations. See Elven et al. (2011) for an extended discussion and with references to Nygren's main works.

The sexual tetraploids in C. purpurascens are found around the North Pacific in the Russian Far East, coastal Alaska and coastal W Canada. The only other close relative at tetraploid level, C. sesquiflora (Trin.) Tzvelev, is a species endemic to the Queen Charlotte Islands in British Columbia at the North Pacific (Elven et al. 2011). There is a single, not confirmed report of a tetraploid also in temperate E North America (Greene 1980, 1984). All arctic plants studied have shrivelled (aborting) anthers and are assumed to have asexual seed reproduction (agamospermy) and probably a higher chromosome number than tetraploid. Two races of C. purpurascens are suggested for E North America including Greenland: the more southern ssp. laricina (Louis-Marie) Elven and the more northern ssp. purpurascens (the type specimen behind the species name is from Melville Island in the Canadian Arctic Archipelago and belongs to this northern race). These races were not accepted by Marr et al. (2007) who had a rather lumping approach to the taxonomy in this genus. The plants in Svalbard are morphologically similar to those of N Greenland and belong to ssp. purpurascens.

How and when did this plant arrive in Svalbard? It is among the more thermophilous of Svalbard plants and not a probable glacial survivor. Its range, even if very small, still includes several separate populations within ca. 80 km². Even if the plant seems to be regularly seed-producing in Svalbard, the chances for fruits to hit the very small spots suitable for it in the present-day vegetation cover (gaps with open silt or sand in an otherwise closed heath vegetation, and the bases of fine-material screes), are small. A hypothesis suggesting that the populations are relicts from a wider distribution in the warmer postglacial period (the Hypsithermal, ca. 7000—2500 years BP) is more probable. The Svalbard material is very uniform, and the congested range suggests that a single successful immigration (probably from Greenland) in the early Postglacial may be responsible for the current-day range.

Elvebakk, A. & Nilsen, L. 2002. Indre Wijdefjorden med sidefjorder: eitt botanisk unikt steppeområde. – Rapport Sysselmannen Svalbard, utgitt av Universitetet i Tromsø. 66 pp.

Elven, R., Murray, D.F., Razzhivin, V. & Yurtsev, B.A. (eds.) 2011. Annotated Checklist of the Panarctic Flora (PAF) Vascular plants. http://panarcticflora.org/

Greene, C.W. 1980. The systematics of Calamagrostis (Gramineae) in eastern North America. – Ph.D. Thesis, Harvard Univ., Cambridge, Mass.

Greene, C.W. 1984. Sexual and apomictic reproduction in Calamagrostis (Gramineae) from eastern North America. – American Journal of Botany 71: 285–293.

Marr, K.L., Hebda, R.J. & Greene, C.W. 2007. Calamagrostis Adans. – In: Flora of North America Editorial Committee (eds.), Flora of North America north of Mexico. 24. Magnoliophyta: Commelinidae (in part): Poaceae, part 1: 706–732.