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|Linnaea borealis ssp. longiflora in flower, near the Matanuska Glacier in Alaska|
Linnaea is a plant genus which has often been classified in the family Caprifoliaceae (the Honeysuckle family) but may be more accurately considered to belong to its own family, Linnaeaceae. The genus includes a single, generally boreal to subarctic woodland subshrub species, Linnaea borealis, commonly known as twinflower (sometimes written twin flower).
The genus Linnaea is now considered to include only a single, circumboreal species, Linnaea borealis, with three subspecies generally recognized:
- Linnaea borealis subsp. borealis - Europe
- Linnaea borealis subsp. americana - North America (formerly classified as the species Linnaea americana)
- Linnaea borealis subsp. longiflora - Asia, and western North America (from Alaska to California)
The genus Linnaea is usually treated in the Caprifoliaceae, along with Lonicera, Symphoricarpos, and related genera, but sometimes classified in its own family Linnaeaceae, along with such similar genera as Abelia, Dipelta, Kolkwitzia, and Zabelia, but not Lonicera or Symphoricarpos.
Linnaea is one of the few kinds of plants or animals to be named after Carl Linnaeus, who knew it well from his explorations of Lapland in northern Sweden in 1732. It was his favorite plant, and as young man, he named it "Linnæa" (now transliterated as "Linnaea"). However, in his Systema Naturae (first published in 1735), Linnaeus instead called this plant "Rudbeckia", for Olaus Rudbeck and his son Olof Rudbeck, Lapland explorers who knew the species. (Later, in his Species Plantarum of 1753, Linnaeus used the genus name Rudbeckia instead for a quite different plant in the Asteraceae, still known by that name).
The genus name Linnaea was first published by Linnaeus' teacher Jan Frederik Gronovius, with the name formalized under the modern system of botanical nomenclature by Linnaeus himself in 1753 in his Species Plantarum, where Linnaeus also formally described and named the species Linnaea borealis, with the epithet "borealis" referring to its northern distribution.
The common name "twinflower" for Linnaea borealis refers to the plant's paired flowers.
The perennial stems of Linnaea are slender, pubescent, and prostrate, growing to 20–40 centimetres (7.9–15.7 in) long, with opposite evergreen rounded oval leaves 3–10 millimetres (0.12–0.39 in) long and 2–7 mm (0.079–0.276 in) broad. The flowering stems curve erect, to 4–8 cm (1.6–3.1 in) tall, and are leafless except at the base. The flowers are paired, pendulous, 7–12 mm (0.28–0.47 in) long, with a five-lobed, pale pink corolla.
Ecology and distribution
Linnaea borealis has a circumpolar distribution in moist subarctic, boreal, or cool temperate forests, extending further south at higher elevations in various mountains, in Europe south to the Alps, in Asia south to northern Japan, and in North America south to northern California and to Arizona and New Mexico in the west, and to West Virginia (and formerly Tennessee) in the Appalachian Mountains in the east. 
Linnaea borealis is self-incompatible, requiring cross-pollination to produce viable seeds; since pollen dispersal is usually not far, individuals and clonal colonies can become reproductively isolated. Regardless of seed production, Linnaea plants in a particular area often spread by stolons to form clonal patches of the same genotype. Such clonal stands of Linnaea can be long-persisting, in some places remaining extant even if seed is not produced or if seedling germination or establishment does not occur.
The species was presumably common in areas south of its present range during times of Pleistocene ("Ice Age") glaciations, and its clone-forming perennial growth habit has allowed it to survive the subsequent millennia locally within this former range in various high-elevation or otherwise cool and moist habitats, including algific talus slopes with persisting underground periglacial ice.
While the three subspecies of Linnaea borealis are all considered widespread, abundant, and secure in their main, northern ranges, all three subspecies are of conservation concern near the subspecies's range edges or at more southerly, disjunct sites.
In Great Britain, Linnaea borealis ssp. borealis is listed as "nationally scarce", growing mainly in open pine woodlands in Scotland and northernmost England. Foresters consider this plant to be an indicator species of ancient woodlands, often found in association with creeping lady's tresses. It is found in about 50 sites around the country, with most situated in the woods around the Cairngorms; the southernmost locations are four sites in Northumberland and one in County Durham. The sparseness of the sites is responsible for the continued decline of the plant in the country. In Scotland, 37% of L. borealis patches studied consisted of a single genotype, reproducing clonally vegetatively but not producing viable seed. This is a conservation concern because without viable seed, the species may not be able to re-populate restored habitat, and may not be able to adapt to climate change by establishing new populations.
In the United States, Linnaea borealis ssp. americana is of conservation concern in several states along or near the southern edge of the species' range, including Arizona, Iowa, Massachusetts, North Dakota, Pennsylvania, and West Virginia, and was known historically but now considered extirpated or possibly so in Illinois, Indiana, New Jersey, Ohio, Rhode Island, and Tennessee.
Since many of the outlying southern sites for Linnaea borealis are in habitats that are at high elevations or otherwise in cooler microclimates than the surrounding general landscapes, ongoing and prospective climate change has become a significant concern for the conservation of this species in such places, such as Ice Mountain in West Virginia, a low-elevation algific talus slope with persisting buried ice.
Linnaeus took Linnaea borealis as his own personal symbol when he was raised to the Swedish nobility in 1757. In his Critica Botanica (1737), Linnaeus had used Gronovius's name Linnaea as an example to advocate the use of commemorative personal names as botanical names:
|“||it is commonly believed that the name of a plant which is derived from that of a botanist shows no connection between the two...[but]...Linnaea was named by the celebrated Gronovius and is a plant of Lapland, lowly, insignificant, disregarded, flowering but for a brief space — after Linnaeus who resembles it.||”|
Linnaea is the name of a German botanical journal (1826–1822)
- Backlund, A.; Pyck, N. (1998). "Diervillaceae and Linnaeacea, two new families of caprifolioids". Taxon 47 (3): 657–661.
- "Linnaea". Index Nominum Genericorum. Smithsonian Institution. Retrieved 24 October 2011.
- Giblin, David (Editor) (2015). "Linnaea borealis". WTU Herbarium Image Collection. Burke Museum, University of Washington. Retrieved 2015-01-24.
- Sullivan, Steven. K. (2015). "Linnaea borealis". Wildflower Search. Retrieved 2015-01-24.
- "Linnaea borealis". PLANTS Database. United States Department of Agriculture; Natural Resources Conservation Service. 2015. Retrieved 2015-01-24.
- Scobie, A. R.; Wilcock, C. C. (2009). "Limited mate availability decreases reproductive success of fragmented populations of Linnaea borealis, a rare, clonal self-incompatible plant". Annals of Botany 103 (6): 835–846. doi:10.1093/aob/mcp007.
- Stafleu, Frans A. 1971. Linnaeus and the Linnaeans: the Spreading of their Ideas in Systematic Botany, 1735–1789. Utrecht: International Association for Plant Taxonomy. ISBN 90-6046-064-2. p. 83.
- Core, Earl L. (1975), The Wondrous Year: West Virginia Through the Seasons, Grantsville, West Virginia: Seneca Books, pg 45.
- Visit Småland Retrieved 25 February 2012.
- IPNILinnaea; Ein Journal für die Botanik in ihrem ganzen Umfange. Berlin
- The Linnaeus Link Project in the spring 2005 edition of Nature First, the magazine for Natural History Museum members.
- Species and habitat conservation from Plantlife.org.uk  and 
- Twinflower species profile 
- Media related to Linnaea borealis at Wikimedia Commons