The family Pinaceae (pine family), is in the order Pinales, formerly known as the Coniferales, and includes many of the well-known conifers of commercial importance such as cedars, firs, hemlocks, larches, pines and spruces. It is supported as monophyletic by its protein-type sieve cell plastids, pattern of proembryogeny, and lack of bioflavonoid. It is the largest extant conifer family in species diversity, with between 220-250 species (depending on taxonomic opinion) in 11 genera, and the second-largest (after Cupressaceae) in geographical range, found in most of the Northern Hemisphere with the majority of the species in temperate climates but ranging from sub arctic to tropical. The family often forms the dominant component of boreal, coastal and montane forests. One species just crosses the equator in southeast Asia. Major centres of diversity are found in the mountains of southwest China, Mexico, central Japan and California.

They are trees (rarely shrubs) growing from 2 to 100 m tall, mostly evergreen (except Larix and Pseudolarix, deciduous), resinous, monoecious, with subopposite or whorled branches, and spirally arranged, linear (needle-like) leaves. The female cones are large and usually woody, 2-60 cm long, with numerous spirally-arranged scales, and two winged seeds on each scale. The male cones are small, 0.5-6 cm long, and fall soon after pollination; pollen dispersal is by wind. Seed dispersal is mostly by wind, but some species have large seeds with reduced wings, and are dispersed by birds. Analysis of Pinaceae cones reveals how selective pressure has shaped the evolution of variable cone size and function throughout the family. Variation in cone size in the family has likely resulted from the variation of seed dispersal mechanisms available in the environment over time. All Pinaceae with seeds weighing less than 90mg, are seemingly adapted for wind dispersal. Pines having seeds larger than 100mg are more likely to have benefited from adaptations that promote animal dispersal, particularly by birds. Pinaceae that persist in areas where tree squirrels are abundant do not seem to have evolved adaptations for bird dispersal. The embryos of Pinaceae are multi-cotyledonous, with 3-24 cotyledons.

Boreal conifers have many adaptions for winter. The narrow conical shape of northern conifers, and their downward-drooping limbs help them shed snow, many of them seasonally alter their biochemistry to make them more resistant to freezing, called "hardening".

Classification

Classification of the subfamilies and genera of the Pinaceae family has been subject to debate in the past. Pinaceae ecology, morphology and history have all been used as the basis for methods of analyses of the family. An 1891 publication divided the family into two subfamiles, using the number and position of resin canals in the primary vascular region of the young taproot as the primary consideration. In a 1910 publication, the family was divided into two tribes based on the occurrence and type of long-short shoot dimorphism. A more recent classification divided the subfamilies and genera based on the consideration of features of ovulate cone anatomy among extant and fossil members of the family. Below is an example of the how morphology has been used to classify Pinaceae. The 11 genera are divided into four subfamilies, based on the cone, seed and leaf morphology:

1. Cones biennial, rarely triennial, with each year's scale growth distinct, forming an umbo on each scale. Cone scale base broad, concealing the seeds fully from abaxial view. Seed without resin vesicles. Seed wing holding the seed in a pair of claws. Leaves with primary stomatal bands adaxial (above the xylem) or equally on both surfaces. Subfamily Pinoideae (Pinus)
2. Cones annual, without a distinct umbo. Cone scale base broad, concealing the seeds fully from abaxial view. Seed without resin vesicles, blackish. Seed wing holding the seed loosely in a cup. Leaves with primary stomatal bands adaxial (above the xylem) or equally on both surfaces. Subfamily Piceoideae (Picea)
3. Cones annual, without a distinct umbo. Cone scale base broad, concealing the seeds fully from abaxial view. Seed without resin vesicles, whitish. Seed wing holding the seed tightly in a cup. Leaves with primary stomatal bands abaxial (below the phloem vessels) only. Subfamily Laricoideae (Larix, Cathaya, Pseudotsuga)
4. Cones annual, without a distinct umbo. Cone scale base narrow, with the seeds partly visible in abaxial view. Seed with resin vesicles. Seed wing holding the seed tightly in a cup. Leaves with primary stomatal bands abaxial (below the phloem vessels) only. Subfamily Abietoideae (Abies, Cedrus, Pseudolarix, Keteleeria, Nothotsuga, Tsuga)

References

• Behnke, H. D. 1974. Sieve element plastids of Gymnospermae: Their ultra structure and relation to systematics. Pl. Syst. Evol. 123:1-12.
• Benkman, C. W. 1995. Wind dispersal capacity of pine seeds and the evolution of different seed dispersal modes in pines. Oikos. 73:221-224.
• Farjon, A. 1998. World Checklist and Bibliography of Conifers. Royal Botanic Gardens, Kew. 300 p. ISBN 1-900347-54-7.
• Greene, D. F. and Johnson, E.A. 1990. The dispersal of winged fruits and seeds differing in autorotative behavior. - Can. J. Bot. 68: 2693-2697.
• Liston, A., Gernandt, D. S., Vining, T. F., Campbell, C. S. & Pinero, D. 2003. Molecular phylogeny of Pinaceae and Pinus. Pp. 107-114 in: Mill, R. R. (ed.). Proceedings of the International Conifer Conference. International Society for Horticultural Science, Brugge. [Acta Hort. No. 615.]
• Price, R. A., J. Olsen-Stojkovich, and J. M. Lowenstein. 1987. Relationships among the genera of Pinaceae: an immunological comparison. Syst. Bot. 12:91–97.