Description and differentiation of Pseudolarix amabilis pollen Palaeoecological implications and new identification key to fresh bisaccate pollen

Abstract

The differentiation of Pseudolarix from other bisaccate pollen is considered as a tool to investigate the fossil history of this genus. Using Light Microscope (LM) and Scanning Electron Microscopy (SEM) we performed a descriptive and morphometric analysis of Pseudolarix amabilis (Pinaceae) bisaccate fresh pollen grains. Descriptive differentiation characters from Pinus and from other bisaccates have been established. A morphometric differentiation from pine pollen belonging to Pinus sylvestris type was obtained through a study of twelve living species of Pinus. A new identification key for bisaccate pollen grains of living conifers has been elaborated. Although it is addressed to identification of fresh pollen, the proposed descriptive criteria may also be applicable to well-preserved fossil material. A Pliocene site from N-Italy, rich in Pseudolarix cone scales and needles, was used to test the reliability of the proposed criteria on fossil pollen. We also identified Pseudolarix pollen from the lacustrine sediments from Massif Central (France), about 3 My. We carried out a complementary evaluation of the ecological and climate ranges both of the living species and of the fossil assemblages that included Pseudolarix. This tree was a component of the warm-temperate mixed conifers rainforests of the Cenozoic, a biome yielding, after considerable reduction of floristic diversity, overall conifer decimation, to the modern “mixed mesophytic” and “mixed hardwood” forest types. Although its fossil record reveals a wide distribution in the Northern Hemisphere during the Cenozoic, macrofossils are only scattered. On the other hand, information about the pollen production, aerodynamics and taphonomy of Pseudolarix pollen suggests that this tree is among the properly or moderately over-represented genera in pollen images from its natural habitat. Therefore, its pollen record may add clarifications to palaeoclimate reconstructions of Cenozoic environments.