Pinus classification

''Pinus'', the pines, is a genus of approximately 111 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 based on chloroplast DNA sequencing and whole plastid genomic analysis. Older classifications split the genus into three subgenera – subgenus ''Pinus'', subgenus ''Strobus'', and subgenus ''Ducampopinus'' ( pinyon, bristlecone and lacebark pines) – based on cone, seed and leaf characteristics. DNA phylogeny has shown that species formerly in subgenus ''Ducampopinus'' are members of subgenus ''Strobus'', so ''Ducampopinus'' is no longer used.

The species of subgenus ''Ducampopinus'' were regarded as intermediate between the other two subgenera. In the modern classification, they are placed into subgenus ''Strobus'', yet they did not fit entirely well in either so they were classified in a third subgenus. In 1888 the Californian botanist John Gill Lemmon placed them in subgenus ''Pinus''. In general, this classification emphasized cone, cone scale, seed, and leaf fascicle and sheath morphology, and species in each subsection were usually recognizable by their general appearance. Pines with one fibrovascular bundle per leaf, (the former subgenera ''Strobus'' and ''Ducampopinus'') were known as ''haploxylon pines'', while pines with two fibrovascular bundles per leaf, (subgenus ''Pinus'') were called ''diploxylon pines''. Diploxylon pines tend to have harder timber and a larger amount of resin than the haploxylon pines. The current division into two subgenera (''Pinus'' and ''Strobus'') is supported with rigorous genetic evidence.

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 (2 in ''Pinus'' or 1 in ''Strobus''), the position of the resin ducts in the needles (internal or external), the presence or shape of the seed wings (absent, rudimentary, articulate, and adnate), and the position of the umbo (dorsal or terminal) and presence of a prickle on the scales of the seed cones.

Both subgenera are thought to have a very ancient divergence from one another, having diverged during the late Jurassic.

Subgenus ''Pinus''

Subgenus ''Pinus'' includes the yellow and hard pines. Pines in this subgenus have one to five needles per fascicle and two fibrovascular bundles per needle, and the fascicle sheaths are persistent, except in '' P. leiophylla'' and '' P. lumholtzii''. Cone scales are thicker and more rigid than those of subgenus ''Strobus'', and cones either open soon after they mature or are serotinous.

Section ''Pinus''

Section ''Pinus'' has two or three needles per fascicle. Cones of all species have thick scales, and all except those of '' P. pinea'' open at maturity. 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.
*'' P. densata'' – Sikang pine
*'' P. densiflora'' – Korean red pine
*'' P. henryi'' – Henry's pine
*'' P. hwangshanensis'' – Huangshan pine
*'' P. kesiya'' – Khasi pine
*'' P. latteri''? – Tenasserim pine
*'' P. luchuensis'' – Luchu pine
*'' P. massoniana'' – Masson's pine
*'' P. merkusii'' – Sumatran pine
*'' P. mugo'' – mountain pine
*'' P. nigra'' – Austrian pine
*†'' P. prehwangshanensis''
*'' 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. uncinata''
*'' P. yunnanensis'' – Yunnan pine

Subsection ''Pinaster''

Subsection '' Pinaster'' contains species native to the Mediterranean, as well as '' P. roxburghii'' from the Himalayas. The scales of its cones lack spines. It is named after ''P. pinaster''.
*'' P. brutia'' – Turkish pine
*'' P. canariensis'' – Canary Island pine
*'' P. halepensis'' – Aleppo pine
*'' P. heldreichii'' – Bosnian 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.

Phylogenetic analysis supports ancient divergences within this section, with subsections ''Australes'' and ''Ponderosae'' having diverged during the mid-Cretaceous.

Subsection ''Australes''

Subsection ''Australes'' is native to North and Central America and islands in the Caribbean.

The closed-cone (serotinous) species of California and Baja California, '' P. attenuata'', '' P. muricata'', and '' P. radiata'', are sometimes placed in a separate subsection, ''Attenuatae''.
*'' P. attenuata'' – knobcone pine
*'' P. caribaea'' – Caribbean pine
*'' P. cubensis'' – Cuban pine
*'' P. echinata'' – shortleaf pine
*'' P. elliottii'' – slash pine
*''† P. foisyi'' – extinct
*'' P. glabra'' – spruce pine
*'' P. georginae''
*'' P. greggii'' – Gregg's pine
*'' P. herrerae'' – Herrera's pine
*'' P. jaliscana'' – Jalisco pine
*'' P. lawsonii'' – Lawson's pine
*'' P. leiophylla'' – Chihuahua pine
*'' P. lumholtzii'' – Lumholtz's pine
*'' P. luzmariae''
*†'' P. matthewsii'' – Pliocene, Canada
*'' P. muricata'' – bishop pine
*'' P. occidentalis'' – Hispaniolan pine
*'' P. oocarpa'' – egg-cone pine
*'' P. palustris'' – longleaf pine
*'' P. patula'' – patula pine
*'' P. praetermissa'' – McVaugh's pine
*'' P. pringlei'' – Pringle's pine
*'' P. pungens'' – Table Mountain pine
*'' P. radiata'' – Monterey pine
*'' P. rigida'' – pitch pine
*'' P. serotina'' – pond pine
*'' P. taeda'' – loblolly pine
*'' P. tecunumanii'' – Tecun Uman pine
*'' P. teocote'' – ocote pine
*'' P. vallartensis''

Subsection ''Contortae''

Subsection '' Contortae'' is native to North America and Mexico.
*'' P. banksiana'' – jack pine
*'' P. clausa'' – sand pine
*'' P. contorta''
**''P. c. bolanderi'' – Bolander pine
**''P. c. contorta'' – shore pine
**''P. c. latifolia'' – lodgepole pine
**''P. c. murrayana'' – tamarack pine
*'' P. virginiana'' – Virginia pine

Subsection ''Ponderosae''

Subsection '' Ponderosae'' is native to Central America, Mexico, the western United States, and southwestern Canada, although its former range was possibly much wider as evidenced by upper Miocene fossils belonging to this subsection found in Japan

*'' P. arizonica'' – Arizona pine
*'' P. cooperi'' – Cooper's pine
*'' P. coulteri'' – Coulter pine
*'' P. devoniana'' – Michoacan pine
*'' P. gordoniana''
*'' P. durangensis'' – Durango pine
*'' P. engelmannii'' – Apache pine
*†'' P. fujiii''
*'' P. hartwegii'' – Hartweg's pine
*'' P. jeffreyi'' – Jeffrey pine
*†'' P. johndayensis'' – Oligocene
*'' P. maximinoi'' – thinleaf pine
*'' P. montezumae'' – Montezuma pine
*'' P. ponderosa'' – ponderosa pine
*'' Pinus ponderosa var. willamettensis'' - Willamette Valley Ponderosa Pine
*'' P. pseudostrobus'' – smooth-bark Mexican pine
*'' P. sabiniana'' – gray pine
*'' P. torreyana'' – Torrey pine

Subgenus ''Strobus''

Subgenus ''Strobus'' includes the white and soft pines. Pines in this subgenus have one to five needles per fascicle and one fibrovascular bundle per needle, and the fascicle sheaths are deciduous, except in '' P. nelsonii'', where they are persistent. Cone scales are thinner and more flexible than those of subgenus ''Pinus'', except in some species like '' P. maximartinezii'', and cones usually open soon after they mature.

Section ''Parrya''

Section Parrya has one to five needles per fascicle. The seeds either have articulate (jointed) wings or no wings at all. In all species except for ''P. nelsonii'', the fascicle sheaths curl back to form a rosette before falling away. The cones have thick scales and release the seeds at maturity. This section is native to the southwestern United States and Mexico.

Subsection ''Balfourianae''

Subsection Balfourianae (bristlecone pines) is native to southwest United States.
*'' P. aristata'' – Rocky Mountains bristlecone pine
*'' P. balfouriana'' – foxtail pine
*†'' P. crossii'' - (Chattian; Creede Formation, Colorado)
*'' P. longaeva'' – Great Basin bristlecone pine

Subsection ''Cembroides''

Subsection ''Cembroides'' (pinyons or piñons) is native to Mexico and the southwestern United States.
*'' P. cembroides'' – Mexican pinyon
*'' P. culminicola'' – Potosi pinyon
*'' P. discolor'' – border pinyon
*'' P. edulis'' – Colorado pinyon
*'' P. johannis'' – Johann's pinyon
*'' P. maximartinezii'' – big-cone pinyon
*'' P. monophylla'' – single-leaf pinyon
*'' P. orizabensis'' – Orizaba pinyon
*'' P. pinceana'' – weeping pinyon
*'' P. quadrifolia'' – Parry pinyon
*'' P. remota'' – Texas pinyon or papershell pinyon
*'' P. rzedowskii'' – Rzedowski's pinyon

Subsection ''Nelsonianae''

Subsection ''Nelsonianae'' is native to northeastern Mexico. It consists of the single species with persistent fascicle sheaths.
*'' P. nelsonii'' – Nelson's pinyon

Section ''Quinquefoliae''

Section ''Quinquefoliae'' (white pines), as its name (which means "five-leaved") suggests, has five needles per fascicle except for '' P. krempfii'', which has two, and '' P. gerardiana'' and '' P. bungeana'', which have three. All species have cones with thin or thick scales that open at maturity or do not open at all; none are serotinous. Species in this section are found in Eurasia and North America, and one species, '' P. chiapensis'' reaches Guatemala.

Subsection ''Gerardianae''

Subsection '' Gerardianae'' is native to East Asia. It has three or five needles per fascicle.
*'' P. bungeana'' – lacebark pine
*'' P. gerardiana'' – chilgoza pine
*'' P. squamata'' – Qiaojia pine

Subsection ''Krempfianae''

Subsection ''Krempfianae'' is currently native to Vietnam, with a fossil record extending into the Oligocene. It has two needles per fascicle, and they are atypically flattened. The cone scales are thick and have no prickles. Until 2021, the subsection was considered monotypic, when an Oligocene fossil species was described from Yunnan Province, China.
*'' P. krempfii'' – Krempf's pine
*†'' P. leptokrempfii'' – Oligocene

Subsection ''Strobus''

Subsection ''Strobus'' has five needles per fascicle and thin cone scales with no prickles. Needles tend to be flexible and soft with slightly lighter side underneath. It is native to North and Central America, Europe, and Asia.
*'' P. albicaulis'' – whitebark pine
*'' P. amamiana'' – Yakushima white pine
*'' P. armandii'' – Chinese white pine
*'' P. arunachalensis''
*'' P. ayacahuite'' – Mexican white pine
*'' P. bhutanica'' – Bhutan white pine
*'' P. cembra'' – Swiss pine
*'' P. chiapensis'' – Chiapas pine
*'' P. dabeshanensis'' – Dabieshan pine
*'' P. dalatensis'' – Vietnamese white pine
*'' P. fenzeliana'' – Hainan white pine
*'' P. flexilis'' – limber pine
*'' P. koraiensis'' – Korean pine
*'' P. lambertiana'' – sugar pine
*†'' P. longlingensis'' – Late Pliocene, Mangbang Formation – Yunnan, China
*'' P. monticola'' – western white pine
*'' P. morrisonicola'' – Taiwan white pine
*'' P. parviflora'' – Japanese white pine
*'' P. hakkodensis'' – Hakkoda pine
*'' P. peuce'' – Macedonian pine
*'' P. pumila'' – Siberian dwarf pine
*'' P. ravii''
*'' P. sibirica'' – Siberian pine
*'' P. strobus'' – eastern white pine
*'' P. strobiformis'' – Southwestern white pine (also Chihuahuan)
*'' Pinus stylesii''
*'' P. wallichiana'' – blue pine
*'' P. wangii'' – Guangdong white pine

''Incertae sedis''

Species which are not placed in a subgenus at this time.
*†'' Pinus latahensis'' – Early Eocene, Klondike Mountain Formation, Allenby Formation – Okanagan Highlands Floras
*†'' Pinus macrophylla'' – Early Eocene, Klondike Mountain Formation, Allenby Formation – Okanagan Highlands Floras
*†'' Pinus peregrinus'' – Middle Eocene, Golden Valley Formation, North Dakota, US
*†''Pinus tetrafolia'' – Early Eocene, Klondike Mountain Formation – Okanagan Highlands Floras

See also

* Hybridization in pines (list of pine hybrids)

References

Bibliography

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External links

Tree of Life Web
– favors classification of ''Ducampopinus'' species in ''Strobus''.
NCBI Taxonomy server
– files ''Ducampopinus'' species above as ''Strobus''.

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