Phylogeny and classification of Pinus

We used chloroplast DNA sequences from matK and rbcL to infer the phylogeny for 101 of the approximately 111 species of Pinus (Pinaceae). At the level of subsection and above, the cpDNA tree is congruent with phylogenies based on nuclear DNA with one notable exception: cpDNA sequences from subsect. Contortae are sister to all other North American hard pines rather than occupying a more derived position in the same clade. We used the cpDNA tree plus evidence from nuclear ribosomal DNA and morphology to propose a new classification for the genus. The molecular phylogenies are symmetrical at the deepest branches of the genus, allowing for the delineation of two subgenera, each with two sections that form sister groups. Within sections, clades were slightly asymmetric and sometimes ambiguously resolved. To accomodate ambiguity in some interrelationships, avoid the creation of new ranks, and retain traditional names, we recognised up to three monophyletic subsections per section. Subgenus Pinus (the diploxylon, or hard pines) is divided into the predominantly Eurasian and Mediterranean section Pinus, composed of subsections Pinus and Pinaster, and the strictly North American section Trifoliae, composed of subsections Australes, Ponderosae, and Contortae. Subgenus Strobus (the haploxylon, or soft pines) is divided into the strictly North American section Parrya, composed of subsections Cembroides, Nelsoniae, and Balfourianae, and the Eurasian and North American section Quinquefoliae, composed of subsections Gerardianae, Krempfianae, and Strobus. Mapping of ten morphological and distributional characters indicates that two were diagnostic for infrageneric taxa: the number of vascular bundles per leaf distinguishes subgenus Pinus from subgenus Strobus, and a terminal-positioned umbo on the ovulate cone scale is diagnostic of subsect. Strobus.