Larches are conifers in the genus Larix, in the family Pinaceae. Growing from 20 to 45 m tall (65 to 147 ft),  they are native to much of the cooler temperate northern hemisphere, on lowlands in the north and high on mountains further south. Larches are among the dominant plants in the immense boreal forests of Russia, Canada, and Scandinavia.
Although a conifer, the larch is a deciduous tree and loses its leaves in the autumn. The shoots are dimorphic, with growth divided into long shoots typically 10–50 centimetres long and bearing several buds, and short shoots only 1–2 mm long with only a single bud. The leaves are needle-like, 2–5 centimetres long, slender (under 1 cm wide). They are borne singly, spirally arranged on the long shoots, and in dense clusters of 20–50 needles on the short shoots. The needles turn yellow and fall in the late autumn, leaving the trees leafless through the winter.
Larch cones are erect, small, 1–9 cm long, green or purple, ripening brown 5–8 months after pollination; in about half the species the bract scales are long and visible, and in the others, short and hidden between the seed scales. Those native to northern regions have small cones (1–3 cm) with short bracts, with more southerly species tending to have longer cones (3–9 cm), often with exserted bracts, with the longest cones and bracts produced by the southernmost species, in the Himalayas.
Species and classification
There are 10–15 species; those marked with an asterisk (*) in the list below are not accepted as distinct species by all authorities. In the past, the cone bract length was often used to divide the larches into two sections (sect. Larix with short bracts, and sect. Multiserialis with long bracts), but genetic evidence does not support this division, pointing instead to a genetic divide between Old World and New World species, with the cone and bract size being merely adaptations to climatic conditions. More recent genetic studies have proposed three groups within the genus, with a primary division into North American and Eurasian species, and a secondary division of the Eurasian into northern short-bracted species and southern long-bracted species; there is some dispute over the position of Larix sibirica, a short-bracted species which is placed in the short-bracted group by some of the studies and the long-bracted group by others.
- Larix decidua (syn. L. europaea) European Larch. Mountains of central Europe.
- Larix sukaczewii Russian Larch.* Russia west of Ural Mountains.
- Larix sibirica Siberian Larch. Plains of western Siberia.
- Larix gmelinii (syn. L. dahurica) Dahurian Larch. Plains of central and eastern Siberia.
- Larix kaempferi (syn. L. leptolepis) Japanese Larch. Mountains of central Japan.
- Larix principis-rupprechtii Prince Rupprecht's Larch. Mountains of northern China (Shanxi, Hebei).
- Olgan Larch or Olga Bay Larch (Larix gmelinii var. olgensis) is sometimes treated as a distinct species Larix olgensis.
- Larix potaninii Chinese Larch. Mountains of southwestern China (Sichuan, northern Yunnan).
- Larix himalaica Langtang Larch.* Mountains of central Himalayas.
- Larix mastersiana Masters' Larch. Mountains of western China.
- Larix speciosa Yunnan Larch.* Mountains of southwest China (southwest Yunnan), northeast Burma.
- Larix griffithii (syn. L. griffithiana) Himalayan Larch. Mountains of eastern Himalaya
- Larix laricina Tamarack Larch or American Larch. Parts of Alaska and throughout Canada and the northern United States from the eastern Rocky Mountains to the Atlantic shore.
- Larix lyallii Subalpine Larch. Mountains of northwest United States and southwest Canada, at very high altitude.
- Larix occidentalis Western Larch. Mountains of northwest United States and southwest Canada, at lower altitudes.
Most if not all of the species can be hybridised in cultivation. The best-known hybrid is the Dunkeld Larch Larix × marschlinsii (syn. L. × eurolepis, an illegitimate name), which arose more or less simultaneously in Switzerland and Scotland when L. decidua and L. kaempferi hybridised when planted together.
- Flowers of Japanese larch emerging.jpg
Male (above) and female (below right) cones of Japanese Larch emerging in spring.
- Larix decidua0.jpg
European Larch foliage and cones.
- Larix decidua male cones.JPG
European Larch male "flowers" or strobili.
Larches are prone to the fungal canker disease Lachnellula willkommii (Larch Canker); this is particularly a problem on sites prone to late spring frosts, which cause minor injuries to the tree allowing entry to the fungal spores. In Canada, this disease was first detected in 1980 and is particularly harmful to an indigenous species larch, the tamarack, killing both young and mature trees.
Larches are also vulnerable to Phytophthora ramorum. In late 2009 the disease was first found in Japanese Larch trees in the English counties of Devon, Cornwall and Somerset, and has since spread to the south-west of Scotland. In August 2010 the disease was found in Japanese Larch trees in counties Waterford and Tipperary in Ireland and in 2013 in the Afan Forest Park in south Wales.
Larch is a wood valued for its tough, waterproof, and durable qualities; top quality knot-free timber is in great demand for building yachts and other small boats, for exterior cladding of buildings, and interior panelling. The timber is resistant to rot when in contact with the ground, and is suitable for use as posts and in fencing. The hybrid Dunkeld Larch is widely grown as a timber crop in northern Europe, valued for its fast growth and disease resistance. (EN 350-2 lists larch as slightly to moderately durable, this would make it unsuitable for ground contact use without preservative in temperate climates, and would give it a limited life as external cladding without coatings).
In central Europe larch is viewed as one of the best wood materials for the building of residences. Planted on borders with birch, both tree species were used in pagan cremations.
Larches are often used in bonsai culture, where their knobby bark, small needles, fresh spring foliage, and – especially – autumn colour are appreciated. European Larch, Japanese Larch, and Tamarack Larch are the species most commonly trained as bonsai.
- Rushforth 1986
- Gernandt & Liston 1999
- Semerikov & Lascoux 1999; Wei and Wang 2003, 2004; Gros-Louis et al. 2005
- "Larix olgensis". Germplasm Resources Information Network (GRIN). United States Department of Agriculture.
- European larch canker Natural Resources Canada
- Forestry Commission webpage on Phytophthora ramorum
- "Thousands of Afan Forest trees planted after infected larch". BBC. 21 February 2015. Retrieved 23 February 2015.
- Gernandt, D. S. & Liston, A. (1999). "Internal transcribed spacer region evolution in Larix and Pseudotsuga (Pinaceae)" (PDF). American Journal of Botany (Botanical Society of America) 86 (5): 711–723. JSTOR 2656581. doi:10.2307/2656581.
- Gros-Louis, M.-C., Bousquet, J., Pâques, L. E., & Isabel, N. (2005). Species-diagnostic markers in Larix spp. based on RAPDs and nuclear, cpDNA, and mtDNA gene sequences, and their phylogenetic implications. Tree Genetics & Genomes 1 (2): 50–63. Abstract.
- Rushforth, Keith (1986) . Bäume [Pocket Guide to Trees] (in German) (2nd ed.). Bern: Hallwag AG. ISBN 3-444-70130-6.
- Semerikov, V. L., & Lascoux, M. (1999). Genetic relationship among Eurasian and American Larix species based on allozymes. Heredity 83: 62–70.
- Wei, X.-X., & Wang, X.-Q. (2003). "Phylogenetic split of Larix: evidence from paternally inherited cpDNA trnT-trnF region". Plant Systematics and Evolution 239: 67–77. doi:10.1007/s00606-002-0264-3.
- Wei, X.-X., & Wang, X.-Q. (2004). "Recolonization and radiation in Larix (Pinaceae): evidence from nuclear ribosomal DNA paralogues". Molecular Ecology 13 (10): 3115–3123. PMID 15367124. doi:10.1111/j.1365-294X.2004.02299.x.
- Earle, Christopher J., ed. (2011). "Larix (larch) description". The Gymnosperm Database.
- Givnish, Thomas J. (2002). "Adaptive significance of evergreen vs. deciduous leaves: solving the triple paradox" (PDF). Silva Fennica 36 (3): 703–743.
The larch paradox—Finally, let us turn to one last, enduring ecological paradox: the deciduous habit of larches (Larix) at high latitudes in nutrient-poor peatlands in the northern hemisphere, where evergreen plants are expected to dominate and often do.Quote from p. 729.
- Phillips, D. H., & Burdekin, D. A. (1992). Diseases of Forest and Ornamental Trees. Macmillan ISBN 0-333-49493-8.
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- Eichhorn, Markus (August 2011). "The Larch". Test Tube. Brady Haran for the University of Nottingham.