Larch (Larix)

Larches are conifers in the genus Larix, of the family Pinaceae (subfamily Laricoideae). Growing from 20 to 45 m (66 to 148 ft) tall, 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 boreal forests of Siberia and Canada. Although they are conifers, larches are deciduous trees that lose their needles in the autumn.

Description and distribution
Larches can reach 50–60 m (Larix occidentalis). The larch's tree crown is sparse and the branches are brought horizontal to the stem, even if some species have them characteristically pendulous. Larch shoots are dimorphic, with leaves borne singly on long shoots typically 10–50 centimetres long and bearing several buds, and in dense clusters of 20–50 needles on short shoots only 1–2 mm long with only a single bud. The leaves (light green) are needle-like, 2–5 centimetres long, slender (under 1 cm wide). Larches are among the few deciduous conifers, which are usually evergreen. Other deciduous conifers include the golden larch Pseudolarix amabilis, the dawn redwood Metasequoia glyptostroboides, the Chinese swamp cypress Glyptostrobus pensilis and the bald cypresses in the genus Taxodium. The male flowers (small cones) are orange-yellowish and fall after pollination. The female flowers (or cones) of larches are erect, small, 1–9 cm long, green or purple, brown in ripening and lignify (called now strobilus) 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. The seeds are winged. The larches are streamlined trees, the root system are broad and deep and the bark is finely cracked and wrinkled in irregular plaques. The wood is bicolor, with salmon pink heartwood and yellowish white sapwood. The chromosome number is 2n = 24, similar to that of most of the other trees of the Pinaceae family.

The genus Larix is present in all the temperate-cold zones of the northern hemisphere, from North America to northern Siberia passing through Europe, mountainous China and Japan. The larches are important forest trees of Russia, Central Europe, United States and Canada. They require a cool and fairly humid climate and for this reason they are found in the mountains of the temperate zones, while in the northernmost boreal zones ones they are also found in the plain. At gen. Larix belong to the trees that go further north than all, reaching in the North America and Siberia the tundra and polar ice. The larches are pioneer species not very demanding towards the soil and they are very long-lived trees. They live in pure or mixed forests together with other conifers or more rarely broad-leaved trees.

Species and taxonomy
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. The genus Larix belongs to the subfamily Laricoideae, which also includes the genera Pseudotsuga and Cathaya.
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