Evergreen subshrub. Stems slender, somewhat wiry, elongated, running above ground, minutely downy when young, often glandular-hairy with age, plants stoloniferous after c. 5 years, spreading up to 50 cm per annum, ultimately a colony may be several metres across; from horizontal stems arise many vertical stems, vegetative and reproductive, to a maximum height of 15 cm. Leaves opposite, variable in shape, 5–20 × 3–15 mm, scallop-toothed in the upper half, base tapering to a 2–3 mm petiole, stipules absent. Inflorescences terminal on glandular-hairy lateral branches (often described as peduncles, though technically not); true peduncles subtended by two lanceolate membranous bracts to 2 mm. Flowers nodding, in pairs, fragrant, peduncles glandular-hairy, 0.5–2 cm long, bracteoles two, lanceolate, c. 1 mm. Calyx 2–5 mm, 5-lobed, lobes narrow-lanceolate. Corolla 5–16 mm, 5-lobed, funnel-campanulate, pinkish-white, hairy inside, glabrous outside. Stamens 4, two long and two short, inserted near the base of the corolla tube, anthers included. Ovary 3-celled, 1 cell fertile, 2 sterile. Fruit dry, c. 3 mm, densely glandular hairy, 1-seeded. (Yang & Landrein 2011; Cullen et al. 2011).
Distribution In the far north of the northern hemisphere, in taiga and tundra ecosystems. In some areas further south e.g. Scandinavia and the Pacific Northwest of North America, and in arctic-alpine ecosystems in places such as Scotland and Poland, where it reaches its southern limit.
Habitat Moist but well drained acid soils in a broad range of woodland communities, and occasionally in grasslands and scrub. Woodland habitats are often characterised by Betula, Pinus and Vaccinium spp. in Eurasia. It prefers dappled shade and low levels of disturbance, often colonising mossy rocks, tree stumps, etc.
USDA Hardiness Zone 2
RHS Hardiness Rating H7
Conservation status Least concern (LC)
Taxonomic note The treatment of North American populations of L. borealis is woefully inconsistent. Consequently, two to three subspecies are recognised: subsp. borealis occurs across Eurasia to eastern Alaska; subsp. longiflora (Torr.) Hultén is restricted to the Pacific Northwest of North America, from southern Alaska to northern California, and possibly in adjacent regions across the Bering Sea; and subsp. americana (J. Forbes) Hultén grows across the rest of North America and Greenland. Some authorities sink subsp. americana into subsp. longiflora, whereas others sink it into subsp. borealis.
One reason so many botanists are reluctant to accept an expanded Linnaea (see genus article) may be that L. borealis, for so long the sole species, has become inextricably linked with Linnaeus himself. This beautiful plant of the high-latitudes became Linnaeus’s emblem even within his own lifetime; he was clearly rather fond of it as Bean recounted: ‘In his Critica Botanica (1737), pp. 80–81, Linnaeus himself commented: “Linnaea is a plant of Lapland, lowly, insignificant, disregarded, flowering but for a brief space – from Linnaeus, who resembles it” (Sir Arthur Hort’s translation, p. 64, 1938)’ (Bean 1981).
In Scandinavia, it may be found in the dappled shade of pinewoods, or in deciduous woodlands typically dominated by Betula and Populus (pers. obs.). It is light sensitive, and tends not to enjoy managed forests, preferring the more organic, more variable conditions to be found in undisturbed areas (pers. obs.). Linnaea is a relatively mobile woody plant, spreading considerably in ‘wet’ years and contracting dramatically in dry ones, hence its preference for natural forests where a more diverse mosaic of conditions may be found (Thiem & Buk-Berge 2017). A great many common names, even in the same language, reflect a variety of traditional uses. Several of its names in Nordic countries reference its medicinal properties, useful as a treatment for various skin conditions, for example ‘Nårislegras’ in Norwegian, literally ‘corpse rash grass’ (Thiem & Buk-Berge 2017). Sadly it would be impractical to list all these various names here, but it does seem a shame that these old, colloquial names are perhaps waning from common usage as the more popular – and admittedly prettier – alternative of ‘Linnaea’ sweeps away the products of hundreds of years of ethnobotany.
Although Linnaea (or Corpse Rash Grass, if you prefer) is predominantly a plant of the high latitudes, quite at home in the taiga and tundra, it does occur further south in arctic-alpine plant communities in Eurasia, for example in Scotland, southern Poland, and northern China. The predominantly north-south orientation of North America’s great mountain ranges, on the other hand, has increased its southerly reach here. It is indigenous in 42 US States, where unsurprisingly it occurs in a very broad range of forest communities typified by cool-temperate species, reaching its southern limit in northern Arizona and New Mexico (Howard 1993). Most botanists distinguish populations in the Pacific Northwest as subsp. longiflora (Pacific Twinflower), with funnel-shaped corollas 10–16 mm long, but the treatment of the other North American populations is split. Some authorities, e.g. Plants of the World Online, treat all North American (excluding western Alaskan) populations as subsp. longiflora; others, e.g. E-Flora BC, restrict the use of this name solely to the Pacific Northwest and place the rest in with the Eurasian subsp. borealis, or distinguish them further as subsp. americana, but the latter appears to be a consequence of geography rather than any consistent morphological distinctiveness.
Like many plants from similar environments Linnaea can be extremely difficult to establish in gardens, and very easy to kill. It requires nutrient-poor, moist but well drained acid soils under dappled shade, in a cool climate. There was at one time ‘a well known colony’ in the Sunningdale Nurseries in Berkshire, UK, but it later died: ‘A load of manure was dumped on it’ (Bean 1981)! Although the climate in southern England is probably no longer appropriate, cool woodsy conditions such as existed in those Berkshire pinewoods still give the best chance of success if the aim is to establish a meaningful swathe; in the absence of such conditions, a cool, shaded position in a rock garden is worth trying, so long as it won’t dry out. Curiously, Bean noted that plants of North American provenance tended to grow better in Britain (Bean 1981), perhaps its more southern reach in North America has endowed some populations with greater heat tolerance than their Eurasian counterparts. The provenance of cultivated material may not be apparent, however.
In many parts of its range Linnaea is rapidly becoming a conservation concern. Being self-incompatible, population fragmentation poses a significant threat (Scobie & Wilcock 2009), as do the myriad consequences of climate change, which are likely to drive the species to localised extinctions in its more southerly outposts (nativeplanttrust.org).