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Gooch, N.L., 1992

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Bibliographic Reference

Gooch, N.L., 1992, The evolutionary and biogeographic history of Pseudolarix gordon (Pinaceae): University of California, Berkeley, Ph.D. dissertation, 220 p.

Abstract

This dissertation reports the results of a study on extant and fossil species of Pseudolarix. In this study, the forest type for twenty-three fossil localities where the genus occurred is plotted on a nomogram. Causes for the extinction of the genus from all but a small part of its former range are suggested, and its biogeographic history is compared to that of other relict gymnosperms present in China today. Only two morphologically complete species have been identified in the fossil record, P. wehrii from the early Middle Eocene of Republic, Washington, and P. arnoldii from the early Middle Eocene of Princeton, British Columbia. Both of these species may have arisen in the Paleocene, although there is a Cretaceous record of vegetative remains that may be allied to Pseudolarix. Pseudolarix wehrii appears to have been entirely North American, and its last definite appearance was in the early Middle Eocene of Washington, although it may have lasted into the early Middle Miocene of Alaska. Pseudolarix arnoldii differs morphologically only slightly from the extant P. amabilis. These taxa may represent different varieties of the same species. Pseudolarix amabilis probably had arisen in Asia by the Middle Miocene. Pseudolarix has been associated with many different forest types in the past. Its actual environmental tolerance is greater than that suggested by its present distribution. The genus is presently not in equilibrium with climate due to historical and, secondarily, anthropogenic factors. Pseudolarix had a circumboreal distribution in the Paleocene and Eocene, and dispersed southward as temperatures cooled. The genus became extinct in Europe at the boundary of the Donau/Gunz interglacial and the Gunz 1 glacial stage in the Pleistocene, presumably due to decreasing winter temperatures. In Alaska, the genus became extinct at the Seldovian-Homerian boundary due to decreasing summer temperatures. In the contiguous western United States, the genus became extinct due to increasing summer drought, probably persisting on the coast of Oregon until about 12 Ma. In Japan, the genus became extinct in the Late Pliocene for reasons which are unclear. It is postulated that the genus occurred in the eastern United States, and that it became extinct in this region during one of the glacial periods. However, no fossil specimens of Pseudolarix have been recovered from this region. The biogeographic history of Pseudolarix does not correspond one-to-one with that of any other relict gymnosperm present in East Asia today.

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