Evolutionary History of the Genus Pseudolarix Gordon (Pinaceae)

The fossil record of Pseudolarix (Pinaceae) reveals wide distribution in North America and Eurasia from at least the Early Cretaceous (Berriasian) and possibly the Late Jurassic (Portlandian) to the Plio-Pleistocene. Several hundred reproductive and vegetative remains, representing two species of Pseudolarix, were recovered from sediments of Eocene age on Axel Heiberg and Ellesmere Islands, Canadian Arctic Archipelago. These specimens form the basis for reassessment of the fossil record of the genus and evaluation of morphology and variability of seed-cone scales, winged seeds, leaves, and brachioblasts. Unfortunately, most reports of Pseudolarix lack sufficient details of the character traits of the cone scales, particularly those of the bracts, that are required for identification at the species level. Following review of the known fossil record, only two species are recognized, discrimination being based on differences in length and morphology of the bract subtending the cone scale. One species, the short-bracted form, possesses anatomical and morphological features that conform entirely to the living species P. amabilis (Nelson) Rehder. On the basis of the now considerable data available for both living and fossil material, segregation of the fossil as a distinct species cannot be justified. As interpreted, P. amabilis is an extraordinary example of evolutionary stasis. The second species, P wehrii Gooch, a long-bracted form, appears to represent an extinct lineage of limited range. The spatial and temporal distribution pattern of fossil Pseudolarix indicates that displacement between Eurasia and North America from the Late Jurassic/Early Cretaceous to the Plio-Pleistocene occurred through Beringia and the newly defined Spitsbergen Corridor; the North Atlantic routes were apparently not used by Pseudolarix. Displacement into Europe from eastern Asia was delayed until regression of the Turgai Strait and late Tertiary, after significant global climatic deterioration.