Golden larch, G. Gordon  1858
Pinaceae

Pseudolarix - Golden larch description

Deciduous tree with a single straight or forking trunk bearing regular tiers of widely spreading horizontal branches to form a broad, rounded crown. Bark smooth at first, nonfibrous, flaking and becoming ridged and furrowed with age. Branchlets strongly differentiated into persistent, spurlike short shoots and branch-building, stretched-out long shoots. Winter buds well developed, scaly. Leaves spirally arranged and radiating all around the twigs, those of the shoots tightly crowded in pseudowhorls, those of the long shoots widely spaced. Individual leaves needlelike, soft, straight, flat, the base tapering to a slightly raised attachment scar on the twig.

Plants monoecious. Pollen cones in a cluster from a single bud at the tip of a short shoot, cylindrical and borne on a slender, leafless stalk. Each cone with numerous, densely spirally arranged pollen scales, each bearing and dominated by two large pollen sacs. Pollen grains large (body 45-80 µm long, 70-95 µm overall), with two round air bladders attached to a minutely bumpy oval body, the bladders with a rougher surface. Seed cones single at the tips of short shoots, proportionately short, upright, maturing in a single season and shedding the seeds and scales together. Individual cones with a relatively few spirally arranged triangular seed scales spreading open at an angle to the short cone axis even before maturity, the minute triangular bract (more than half as long as the seed scale in an extinct species) attached only at the base. Seeds two per scale, the body oval, with a much larger asymmetrical, triangular wing derived from the scale and completely covering it while tightly cupping the body on one side and overlapping a little on the other side. Cotyledons four to seven, each with one vein. Chromosome base number x = 22.

Wood soft, light, the yellowish brown heartwood little differentiated from the tan sapwood. Vertical resin canals lacking in normal wood and not produced in response to wounding. Some cells at the edges of the rays near ring boundaries are packed with small crystals.

Stomates arranged in about 12 lines confined to two broad bands covering most of the underside. Each stomate sunken beneath and partly hidden by the four (to six) surrounding subsidiary cells, which are often shared between adjacent stomates in the same little and which have a very thin cuticle (typical of deciduous conifers) showing no trace of a Florin ring. Leaf cross section with a single-stranded midvein flanked by small wedges of transfusion tissue and surrounded by a ring of large bundle sheath cells, and with one (to three) pairs of very small resin canals at the outer edges of the leaf. Photosynthetic tissue with a very thick palisade layer beneath the upper epidermis, which is partially lined by a discontinuous thin hypodermal layer, and with a spongy mesophyll consisting of very irregular cells continuing down to the stomatal bands.

One species in China. Published in 1858, the name Pseudolarix has enough technical nomenclatural difficulties that H.E. Moore (1965) proposed a substitute name, Chrysolarix. Not all taxonomists agreed with this arguments, and he, himself, later accepted the original name. The difficulties were formally set aside by nomenclaturally conserving the name with golden larch rather than Japanese larch (Larix kaemferi), as the type. Pseudolarix amabilis is well established in cultivation but not nearly frequently enough used as a handsome specimen for parks and larger gardens. The few cultivars that have been selected are dwarfs of varying habit.

Contrary to its name, Pseudolarix (Greek and Latin for “false larch”) is not related to the larches (Larix), which it resembles only in having deciduous needles on long-lived spur shoots. All other morphological features, including the structure and arrangement of the pollen and seed cones and the anatomy of the needles, ally Pseudolarix with the abietoid genera of the Pinaceae: Abies, Cedrus, Keteleeria, Nothotsuga, and Tsuga. DNA studies and other molecular analyses point to a particularly close relationship to the hemlocks (Tsuga and Nothotsuga), which is somewhat ironic because Larix is closest to Pseudotsuga (the Douglas firs). Nonetheless, the chromosome base number x = 22 is unique in Pinaceae, which otherwise have a base number x = 12 (13 in Pseudotsuga menziesii). This suggests a polyploidy origin for the golden larch, a phenomenon very rare among the conifers, the most spectacular example being the redwood (Sequoia sempervirens), a hexaploid (six sets of chromosomes from up to three different parent species).

The distinctiveness of Pseudolarix is reinforced by one of the oldest fossil records in the family Pinaceae, with convincing fossils from the early Cretaceous, while most other genera (except Pinus) are not recognizable until the Tertiary. Although the single living species is confined to China today, the genus was a little more diverse and much more widespread in the past, with many named species representing as few as two biological species. In the early Cretaceous the genus was confined to Eastern Asia and western North America, spreading throughout boreal North America by the early Tertiary and reaching western Eurasia by the beginning of the Miocene. By the end of the Miocene, this broad distribution was fragmenting, and Pseudolarix disappeared from North America during the Miocene, from Japan at the end of the Pliocene, and from Europe soon thereafter. 

References

• Farjon, A. (2010). A Handbook of the World's Conifers. Koninklijke Brill, Leiden.
• Eckenwalder, J.E. (2009) Conifers of the World: The Complete Reference. Timber Press, Portland.
• IUCN Red List of Threatened Species, International Union for Conservation of Nature and Natural Resources. Cambridge, UK /Gland, Switzerland

Copyright © Aljos Farjon, James E. Eckenwalder, IUCN, Conifers Garden. All rights reserved.