Pinus massoniana Lambert, a species with long slender needles of about 12–20 cm, is an endemic conifer distributed mostly in southern, central and eastern part of China. Some populations of P. massoniana are also found in Hainan Province, but the paleogeographical evidence for distribution pattern is lacking.

Prof. ZHOU Zhekun and his team at Xishuangbanna Tropical Botanical Garden (XTBG) of Chinese Academy of Sciences collected some well-established cone fossils from outcrops located in Dashidong Village (23°15′N, 104°15′E, 1482 m a.s.l.), Wenshan prefecture, Southeast Yunnan, China. The fossil remains include a three-imensional seed cone and associated needles which have well preserved cuticles. The fossil seed cone and associated needles from the upper Miocene Wenshan Flora show identical morphological characters to P. massoniana.

The researchers compared the fossils with the extant variants in the genus Pinus (P. massoniana var. shaxianensis Zhou, P. massoniana var. massoniana Lambert and P. massoniana var. hainanensis Cheng et Fu). The comparison results showed that the fossils closes resemble P. massoniana var. hainanensis, a tropical montane thermophilic and hygrophilous plant restricted to Hainan Island.

Based on the differences in morphological features of seed cones, tree variations among extant Pinus massoniana have been recognized. The present discovery of Pinus massoniana var. hainanensis in Southwest China and P. massoniana var.massoniana from Southeast China suggests that the differentiation within P. massoniana began in the late Miocene or earlier.

The extant P. massoniana var. hainanensis grows in a humid subtropical to tropical climate. With the global cooling in the Late Neogene, the climate in Hainan has changed accordingly. The cooler climate provided suitable conditions for the southward expansion of Pinus massoniana var. hainanensis. Therefore, these southern populations of P. massoniana var. hainanensis may have behaved as minor, secondary refugia in the Quaternary Period, and are of comparatively recent origin.

The climatic context of Pinus massoniana from the upper Miocene of Wenshan indicates a warm and humid climate. Lower temperatures would be adverse to the germination of the P. massoniana seeds. The researchers suggested that the disappearance of P. massoniana from southwestern part of China is likely related to the amplification of monsoon climate after the late Miocene.

The study entitled “The occurrence of Pinus massoniana Lambert (Pinaceae) from the upper Miocene of Yunnan, SW China and its implications for paleogeography andpaleoclimate” has been published in Review of Palaeobotany and Palynology.

 Figure 1: Pinus massoniana-like ovulate cone (Image by ZHANG Jianwei)  

Figure 2: Comparisons of fossil with extant species, showing similar morphological features between them in apophyses, umbos, mucros and epidermal structures. (Image by ZHANG Jianwei)