"In nature's infinite book of secrecy, A little I can read." -- William Shakespeare

Classification of the Genus Pinus

Acknowlegment : the following taxonomy of the genus Pinus
was completely revised by Michael Frankis (Newcastle, UK),
December 1999 & January 2002.

There are three main categories of pine trees, the subgenus Strobus (white or "soft") pines, the subgenus Ducampopinus (pinyon, foxtail and lacebark pines), and the subgenus Pinus (yellow or "hard") pines.

There is a choice of different morphological characteristics on which to base classification and therefore (especially in the subgenus Pinus) some very different classification schemes. For a better understanding of morphology, please select #1. "What are Pines Trees" and #14. "Pine Cones" in the Directory.

The basic classification into the three subgenera is very easy from cone, seed and leaf characters:

1. Scale without a sealing band. Umbo terminal.
Seedwings adnate. One fibrovascular bundle per leaf.
subgenus Strobus
2. Scale without a sealing band. Umbo dorsal.
Seedwings articulate. One fibrovascular bundle per leaf.
subgenus Ducampopinus
3. Scale with a sealing band. Umbo dorsal.
Seedwings articulate. Two fibrovascular bundles per leaf.
subgenus Pinus

Notice that in many respects, subgenus Ducampopinus is intermediate between (and possibly ancestral to) the other two subgenera. In many classifications, it is combined into subgenus Strobus, but it could with equal justification have been included in subgenus Pinus (as was done in an early classification by the Californian botanist J. G. Lemmon in 1888), yet it does not sit comfortably in either so is best treated as a third subgenus in its own right.

The following classification of pines mostly follows Little and Critchfield's classification (USDA Forest Service Misc. Pub. No. 1144, 1969) with modifications and additions from Michael Frankis (pers. comm.), Jesse P. Perry (The Pines of Mexico and Central America, Timber Press, 1991), Keith Rushforth (Conifers, Christopher Helm Publishers, 1987) and Ecology and Biogeography of Pinus, edited by David Richardson (Cambridge University Press, 1998) - please see Directory # 26 "Books". In general, cone and cone scale and seed morphology and leaf fascicle and sheath morphology are emphasized and this seems to result in a classification that has subsections of pines that are understandable and usually readily recognized by their general appearance.

The box format below was designed by Arboretum de Villardebelle. Please check this site for other conifer classifications.
SUBGENUS STROBUS    White or Soft Pines
The defining morphology:  Cone scales with a terminal umbo and no sealing band.  Adnate (firmly attached) seedwings.  One fibrovascular bundle per leaf.
Other features:  Resin canals in the outer part of the leaf; leaves in clusters of 5; leaves in fascicles of 5; leaf sheaths soon deciduous; leaf stomata usually confined to the inner surfaces, creating two macroscopic narrow white lines on the inner leaf surfaces; the bases of the leaf bracts are non-decurrent, leaving a smooth branch after the leaves are shed; bark is generally smooth, becoming rough only at an older age. Shoots uninodal (producing only one whorl of branches per year). Wood is generally white and soft with less prominent annual rings (better for carving) and with smooth-walled tracheids and fewer resin canals; terpene analysis often shows a high % of beta-pinene.
Section Quinquefoliae (a.k.a. section Strobus)  White Pines
The defining morphology: as for the subgenus.
Subsection Strobi
Features: Cones long and narrow, opening at maturity. 

In some, the seeds are small with a long wing, others [marked * right] have large seeds with a short wing as in subsection Cembrae, and are likewise bird-dispersed - an example of parallel evolution.

Species: strobus, monticola, *flexilis, *reflexa, *strobiformis, ayacahuite, chiapensis, peuce, wallichiana, bhutanica, dalatensis, *armandii, *dabeshanensis, lambertiana, *amamiana, *fenzeliana, morrisonicola, wangii, *parviflora, *pumila
(North & Central America, Europe, Asia). 
Significant synonyms:
ayacahuite var. brachyptera = strobiformis
griffithii = wallichiana
kwangtungensis = wangii
Subsection Cembrae
Features:  Cones do not open at maturity, but instead are broken up by birds which disperse the seeds (see book #6 in the book list); large seeds with the seed wing reduced to a narrow rim. Species:  cembra, sibirica, koraiensis, albicaulis
(Europe, northern Asia, western North America)

SUBGENUS DUCAMPOPINUS    Pinyon, Lacebark and Foxtail Pines
The defining morphology:  Cone scales with a dorsal umbo and no sealing band.  Articulate (easily removed) seedwings.  One fibrovascular bundle per leaf.
Other features: Leaves in clusters of 1 to 5; leaf sheaths variably deciduous to persistent, in many forming a recurved basal rosette; bases of the leaf bracts not or moderately decurrent, leaving a moderately smooth branch often with small pulvini after the leaves are shed; bark is generally smooth (becomes rough at an older age in most but not all species); wood hard and resinous, with smooth-walled tracheids; shoots uninodal (producing only one whorl of branches per year) but summer ('lammas') growth (a second full flush) occuring on vigorous shoots of many species. Most are small, slow-growing trees with irregular rounded crowns, but many are long-lived, some exceptionally so. Generally, a very ancient group with diverse morphology, and most species with small relictual ranges; most are highly specialised to difficult sites where few or even no other trees will grow (one or more of low rainfall; infertile rocky sites; serpentine; limestone; very high altitudes); most are rare and many are endangered.
Section Parrya
The defining morphology: A heterogenous group, sharing nothing beyond the main features of the subgenus (above), they would be better treated in several sections (mostly yet to be formally named) corresponding to the subsections below, which are ancient groups that diverged from each other long ago.
Subsection Nelsonianae Nelson's Pinyon
Features: Cylindrical cones with indistinct umbos (no resting period), on long stout curved stalks; seeds large, with a vestigial wing. Leaves 3 per fascicle, but appearing single, 'zipped' together (can be separated with difficulty); sheath persistent. Species: nelsonii
(northeastern Mexico)
Subsection Krempfianae Krenpf's Pine
Features: Small winged seeds, small cones. Leaves 2 per fascicle, very broad (3-7mm wide) and flat; sheath deciduous. Species: krempfii
Subsection Gerardianae Lace-bark pines
Features: Distinctive smooth exfoliating bark even on old trees. Glossy, often fairly stout needles grouped in fascicles of 3 (-4); fully deciduous needle sheath. Very short seed wings (except long in P. squamata). Species: gerardiana, bungeana, squamata
(Central Asia).
Subsection Rzedowskianae Big-cone pinyons
Features: Long cylindrical cones (5-22 cm long); large seeds, usually with a very short wing (except long in P. rzedowskii). Leaves moderately long (6-12cm), 3 - 5 per fascicle; sheath semi-persistent, forming a rosette, or fully deciduous. Species: pinceana, maximartinezii, rzedowskii
Subsection Cembroides Pinyons [Piņons], a.k.a. Nut pines
Features: Large seeds with a very short, easily detached wing that remains attached to the cone scale; short globose cones, 2.5-8 cm long. Leaves short (2-6 cm), 1-5 per fascicle; sheath semi-persistent, forming a rosette. Species: monophylla, edulis, remota, cembroides,  quadrifolia, discolor, johannis, culminicola, orizabensis
(Mexico and SW United States).
Significant synonyms:
juarezensis = quadrifolia
discolor = johannis var. bicolor
Subsection Balfourianae Foxtail pines
Features: Extreme longevity of trees. Seeds small with long articulate wings; cones cylindrical. Leaves short, in fascicles of 5; sheath semi-persistent, forming a rosette; leaves long-retained (10-35 years), with bottlebrush-like ("foxtail") arrangement on branches. Species: balfouriana, longaeva, aristata
(SW United States).

SUBGENUS PINUS    Typical, Yellow or Hard Pines
The defining morphology: Cone scales with a dorsal umbo and a sealing band. Seedwings usually articulate (easily removed). Two fibrovascular bundles per leaf.
Other features: Resin canals in the intermediate or inner portion of the leaves; fascicles of 2 -5 (rarely up to 8) leaves; leaf sheaths are persistent (except in subsection Leiophyllae); leaf stomata on both ventral and dorsal surfaces; the bases of the leaf bracts are decurrent, leaving a rough branch after the leaves are shed (except P. pseudostrobus, P. apulcensis and P. maximinoi, where the bract bases are decurrent but fairly smooth); bark is generally thick and fissured; wood is generally harder and yellower and with more prounced annual growth rings; growth of spring shoots is either uninodal or multinodal; high % of alpha-pinene in many (but not all) species.
Section Pinus Eurasian Hard Pines
The defining morphology: Wood with large ('fenestriform') ray cell pits; 2 pairs (other pines have only 1 pair) of heterobrachial chromosomes (in which the long arm is more than 2x the length of the short arm); shoots always uninodal.
Subsection Pinus
Features: As for the section. Leaves in fascicles of 2-3; small cones, mature in 18 months with moderately flexible scales (stiff in P. yunnanensis, P. kesiya), opening early and falling completely from the branch (moderately persistent in a few). Species: sylvestris, densiflora, tabuliformis, densata, taiwanensis, mugo, nigra, heldreichii, thunbergii, luchuensis, hwangshanensis, massoniana, resinosa, tropicalis, yunnanensis, kesiya
(Europe, Asia; also P. resinosa in northeast North America and P. tropicalis in Cuba).
Significant synonyms:
uncinata = mugo subsp. uncinata
leucodermis = heldreichii
henryae = tabuliformis var. henryae
insularis = kesiya
Section Pinea Mediterranean Pines
The defining morphology: Glossy red-brown to nut-brown cones with thick, stiff, woody scales, often long-persistent; bright (often yellowish-) green leaves in fascicles of 2-3, thick plated red-brown bark. Wood with small ray cell pits.
Subsection Pineae
Features: Very large seed with very rudimentary wing, cones mature in 36 months. Species: pinea
(western Mediterranean; probably ancient human introduction in the east Med. but possibly native there)
Subsection Pinaster
Features: Moderately large seed with long wing; cones mature in 24 months (12 months in tropical P. latteri, P. merkusii). Shoots often multinodal; leaves in fascicles of 2-3; sheath persistent. Species: pinaster, canariensis, roxburghii, halepensis, brutia, latteri, merkusii
(Mediterranean, southern Asia).
Significant synonyms:
eldarica = brutia subsp. eldarica
Section Trifoliae American Hard Pines
The defining morphology:  A hard group to define. All but two American "hard" pines belong to this section. Wood with small ray cell pits. Vigorous shoots mostly multinodal (except subsection Ponderosae, uninodal). Subsections Taedae, Contortae and Oocarpae are not reliably separable on morphology; their separation depends mainly on barriers to experimental hybridisation. Subsection Ponderosae may yet prove to be better treated as a full section.
Subsection Leiophyllae
The defining morphology: Deciduous leaf sheath.
Other features: Leaves 3-5 per fascicle. Cones mature in 24-30 months; small seed with long detachable wing. Species: leiophylla, lumholtzii
(Mexico, southwest United States).
Significant synonyms:
chihuahuana = leiophylla subsp. chihuahuana
Subsection Australes
The defining morphology: None that reliably separates it from subsections Contortae or Oocarpae. The three subsections share fairly straight branching, not candelabra-like; multinodal shoots (more than 1 branch whorl per growing season on vigorous shoots); 2-3 (-5) leaves per fascicle; cones mature in 16-20 months, scales with a persistent umbo spine; small seed with long detachable wing (rarely weakly adnate in P. palustris, P. caribaea).
Other features: Mostly symmetrical cones, opening when ripe and falling complete (except persistent and often serotinous in P. pungens, P. rigida, P. serotina). Species: palustris, echinata, glabra, serotina, rigida, virginiana, clausa, pungens, taeda, hondurensis, elliottii, caribea, occidentalis, cubensis
(North & Central America, Caribbean).
Significant synonyms:
australis = palustris
caribaea var. hondurensis = hondurensis
Subsection Contortae
The defining morphology: See subsection Taedae
Features: Cones small, symmetrical or oblique, and often closed when ripe (serotinous). Leaves short (< 8 cm), 2 per fascicle. Species: contorta, banksiana
(Canada, United States, Mexico [Baja California] )
Significant synonyms:
murrayana = contorta subsp. murrayana
Subsection Oocarpae
The defining morphology: See subsection Taedae
Features: Cones often oblique and mostly remaining closed on the branch long after they are ripe (serotinous); but soon opening in teocote, herrerae, lawsonii, tecunumanii; leaves in fascicles of 2-5. Species: attenuata, muricata, radiata, greggii, patula, teocote, herrerae, lawsonii, tecunumanii, pringlei, jaliscana, praetermissa, oocarpa
(Central America, Mexico, western United States).
Subsection Ponderosae (including subsection Sabinianae)
The defining morphology: Branching candelabra-like, with upcurved branches, erect uninodal shoots with spreading leaves resembling a chimney sweep's brush. Symmetrical or slightly oblique cones; cones mature in 18 months (22 in P. torreyana), open when ripe, and some cone basal scales remain on the branch after the cone has fallen (except in P. maximinoi, P. gordoniana).
Other features: Leaves often long to very long, often stout, (2-) 3-5 (-8) per fascicle. Cone scale umbo mostly with a curved spine. Species: torreyana, sabiniana, coulteri, jeffreyi, ponderosa, arizonica, engelmanii, durangensis, hartwegii, cooperi, estevezii, montezumae, devoniana, pseudostrobus, apulcensis, maximinoi, gordoniana
(Central America, Mexico, western United States, southwest Canada).
Significant synonyms:
washoensis = ponderosa
rudis = hartwegii
oaxacana = apulcensis
douglasiana = gordoniana

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