Plant 131

Larix species (Pinaceae)



Larches are distinctive, deciduous conifers distributed through Eurasia and North America. Larches have two types of shoots: long shoots with spirally arranged leaves; and short shoots with a terminal tuft of leaves. Similar leaf arrangements are found in the genera Pseudolarix and Cedrus but they are readily separated from Larix. Pseudolarix is deciduous but the scales of its female cone are woody and fall off at maturity, whilst Cedrus is evergreen.

The genus comprises ten species, of which three (Larix gmelinii, Larix laricina, Larix russica) are widespread in northern boreal forests at low elevations. The other species have much more restricted distributions, occupying habitats at montane and subalpine elevations. Members of the genus appear well adapted to cold climates and short growing seasons but are intolerant of shade and waterlogged conditions.

The European larch (Larix decidua) is the only native European Larix species but is restricted to parts of the Alps and the Carpathian mountains. However, European larch has been widely introduced across the continent and other temperate regions of the world; in parts of New Zealand it is considered to be an invasive species. The earliest records of the species growing in Britain date from the early seventeenth century, where it was grown as a horticultural curiosity. Over the last century European larch and hybrid larch (Larix x marschlinsii) have become important timber and amenity trees.

Hybrid larch accidentally originated in Scotland on the Duke of Atholl's estate at Dunkeld in the early twentieth century. The Duke planted Japanese larch (Larix kaempferi), endemic to hills and mountains of Central Honshu (Japan), and European larch together in 1885. Trees raised from seed collected on the estate proved to grow better than either European or Japanese larch; subsequently the trees were shown to be first-generation hybrids. So-called hybrid vigour declines over subsequent hybrid generations. For commercial production of hybrid larch, first-generation hybrids are generated in hybrid seed orchards planted with both parents. Hybrid larch illustrates one of the consequences of serendipitous crossings, when species are brought together in cultivation.

Investigations of evolutionary relationships among larch species, using limited sampling of chloroplast and nuclear DNAs, have frequently proved conflicting. These studies generally recognise three groups of species: the North American species, the South Asian species and the north Eurasian species. However, the processes that might explain these patterns are unclear and point to the need for more detailed research to be conducted.

Farjon A 2016. Conifers of the world. Resources for conifer research. Department of Plant Sciences, University of Oxford.

Farjon A and Filer DF 2013. An atlas of the world's conifers. Brill.

Semerikov VL et al. 2003.Conflicting phylogenies of Larix (Pinaceae) based on cytoplasmic and nuclear DNA. Molecular Phylogenetics and Evolution 27: 173-184.

Stephen Harris