Pinus leptokrempfii, an Oligocene Relative of the Flat-Needled Pine PINUS krempfii (Pinaceae) from China: Implications for Paleogeographic Origin

Abstract

Premise of research. The geographic origin of Pinus krempfii Lecomte, an unusual pine endemic to Vietnam, is unknown, as are the fossil relatives of this species. Its affinity and classification are also problematic. Morphological and systematic studies have shown that this species differs from all other pines in its falcate, lanceolate, and flat needles. Fossils can provide evolutionary and systematic clues for such extant species.Methodology. Fossil leafy twigs were discovered in the early Oligocene Wenshan flora, Yunnan Province, southwestern China. The morphological variation of these fossils was compared with the morphology of extant species in the genus Pinus. On the basis of these comparisons, the close affinity of the fossils to the extant P. krempfii is discussed.Pivotal results. The Chinese fossils were assigned to P. leptokrempfii sp. nov., which is interpreted as most closely related to extant P. krempfii on the basis of morphological similarities such as falcate and flat needles. It differs from the extant species, which possesses only two-needled fascicles, by possessing two- or three-needled fascicles and longer, narrower needles.Conclusions. Relatives of P. krempfii occurred in the early Oligocene in subtropical mixed mesophytic forests that covered an area corresponding to present-day eastern Asia and eastern and western North America. Since the early Oligocene, global cooling and the monsoon climate in southern China may have induced the southward expansion and differentiation of P. leptokrempfii. The needles of P. krempfii, which are shorter and broader than those of P. leptokrempfii, may have evolved to adapt to the warmer, more humid climate in present-day Vietnam.