Pinus, the pines, is a genus of approximately 110–120 extant tree and shrub species. The genus is currently split into two subgenera, subgenus Pinus (hard pines), and subgenus Strobus (soft pines). Each of the subgenera have been further divided into sections and subsections based in the past on morphology, ecology and biogeography, and more recently increasingly from chloroplast DNA sequencing and whole plastid genomic analysis. While the genetic analysis has given robust results at the higher levels, they often give conflicting results lower in the phylogenetic trees, with species allocated to different subsections (and sometimes different sections) by different studies or even within a study. Within subsections, the genetic relationships between species can be even more complex and conflicting; in one study, three samples of the very distinctive and morphologically constant Pinus lambertiana were placed in three different clades of the subsection Strobus, and similar problems with many other species with widespread nonmonophyly.
Several features are used to distinguish the subgenera, sections, and subsections of pines; the number of leaves (needles) per fascicle, whether the fascicle sheaths are deciduous or persistent, the number of fibrovascular bundles per needle (two in Pinus, one in Strobus), the position of the resin ducts in the needles (internal or external), the presence or shape of the seed wings (rudimentary or effective, articulate or adnate), and the position of the umbo (dorsal or terminal) and presence of a prickle on the scales of the seed cones. The two subgenera are thought to have ancient divergence from each other, having diverged at some point between the late Jurassic (around 160 million years ago), the mid Cretaceous (around 125 million years ago), to the late Cretaceous (around 100 million years ago).
Subgenus Pinus Subgenus Pinus includes the yellow and hard pines. Pines in this subgenus have two to five needles per fascicle (rarely as many as eight, in P. durangensis). They have two fibrovascular bundles per needle, and the fascicle sheaths are persistent, except in P. leiophylla and P. lumholtzii. The cone scales are thicker and more rigid than those of subgenus Strobus, and have a resin sealing band before opening (resulting in the cones opening with an audible crack); the cones either open soon after they mature or are serotinous.
Section Pinus Section Pinus has two or three needles per fascicle. The cones have moderately thin to thick scales; in most they open at maturity, but are weakly serotinous in some species in subsection Pinaster. Species in this section are native to Europe, Asia, and the Mediterranean, except for P. resinosa in northeastern North America and P. tropicalis in western Cuba. Subsection Incertae sedis
†P. driftwoodensis – Early Eocene, British Columbia, Canada
Subsection Pinus
All but two species (P. resinosa and P. tropicalis) in Subsection Pinus are native to Eurasia. The cones have moderate thickness scales, and are characterised by a slightly off-centre prickle ('excentromucronate') on the umbo.
P. densata – Sikang pine P. densiflora – Japanese red pine or Korean red pine P. henryi – Henry's pine P. hwangshanensis – Huangshan pine P. kesiya – Khasi pine P. luchuensis – Luchu pine P. massoniana – Masson's pine P. mugo – mountain pine P. m. subsp. mugo P. m. subsp. uncinata (treated as a separate species P. uncinata by POWO, but with minimal genetic distinction from P. mugo) P. nigra – Austrian pine P. resinosa – red pine P. sylvestris – Scots pine P. tabuliformis – Chinese red pine P. taiwanensis – Taiwan red pine P. thunbergii – Japanese black pine P. tropicalis – tropical pine P. yunnanensis – Yunnan pine †P. prehwangshanensis †P. yorkshirensis
Subsection Incertae sedis This pine is commonly resolved into subsection Pinaster by genetic studies, but this is in strong conflict with its morphology and ecology, which is much closer to subsection Pinus, or alternatively placed in its own subsection Leucodermes close to subsection Pinus.
P. heldreichii – Bosnian pine
Subsection Incertae sedis These pines are placed in subsection Pinus by some genetic studies, but in subsection Pinaster by others. In morphology and ecology, they belong in the latter group. The subsection Merkusia has also been proposed for them.
P. latteri – Tenasserim pine P. merkusii – Sumatran pine P. ustulata – Philippine pine (split from P. merkusii in 2014)
Subsection Pinaster
Subsection Pinaster contains species native to warm climates in the Mediterranean region at low altitudes, as well as P. roxburghii from the Himalayas. The cones are thick-scaled and orange-brown to red-brown, and the cone scales are glossy and lack umbo spines. It is named after P. pinaster.
P. brutia – Turkish pine P. canariensis – Canary Islands pine P. halepensis – Aleppo pine P. pinaster – maritime pine P. pinea – stone pine P. roxburghii – chir pine
Section Trifoliae Section Trifoliae (American hard pines), despite its name (which means "three-leaved"), has two to five needles per fascicle, or rarely eight. The cones of most species open at maturity, but a few are serotinous. All but two American hard pines belong to this section. The timing of divergences within this section is disputed, with subsections Australes and Ponderosae having diverged during the mid Cretaceous (about 110 million years ago) according to one study, but not until the mid Oligocene (about 30–35 million years ago) in others.
Subsection Attenuatae
The three closed-cone (serotinous) and fire adapted species of California and Baja California form a small subsection; closely related to, and often included within subsection Australes. Some studies suggest Pinus glabra may also belong here (despite its morphological dissimilarity) though others include it in subsection Australes.
P. attenuata – knobcone pine P. muricata – Bishop pine P. radiata – Monterey pine
Subsection Australes
This subsection is native to North and Central America and islands in the Caribbean. It has 26 living species.
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