A Reassessment of Tibetan Hard Pine, Pinus densata, on the Basis of Morphologyand Biogeography of the P. kesiya Complex (Pinaceae)

ABSTRACT Pinus densata, universally considered a Tertiary hybrid species, was studied throughout its distribution range, together with all the related species that form the P. kesiya complex. The heterogeneously classified pine populations of this complex from the Tibetan region of the Brahmaputra catchment area are distinguished as a new subspecies, Pinus densata subsp. tibetica, characteristic of deep valley systems under 3000 m. In areas in N Yunnan and S Sichuan, where populations of P. densata and P. yunnanensis have been in recent contact, secondary introgressive hybridization was distinguished and a new hybrid, P. × naxiorum, is described. Biogeographic data for P. densata subsp. tibetica (including a distribution map for both subspecies) are given, along with data from a discovered eastern site of P. densata var. pygmaea. Akey that partially revises the key from Flora of China and summarizes the taxa of the P. kesiya complex and other similar taxa is given. A hypothesis of the phylogeography of P. densata is formulated based on the compilation of available data.