|
Larches are conifers in the genus ''Larix'', in the family Pinaceae. Growing from 20 to 45 m tall (65 to 147 ft), 〔Rushforth 1986〕 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〔Gernandt & Liston 1999〕 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;〔Semerikov & Lascoux 1999; Wei and Wang 2003, 2004; Gros-Louis et al. 2005〕 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Larch」の詳細全文を読む スポンサード リンク
|