The Pinaceae, or pine family, are conifer trees or shrubs, including many of the well-known conifers of commercial importance such as cedars, firs, hemlocks, larches, pines, and spruces. The family is included in the order Pinales, formerly known as Coniferales. Pinaceae have distinctive cones with woody scales bearing typically two ovules, and are supported as monophyletic by both morphological trait and genetic analysis. They are the largest extant conifer family in species diversity, with between 220 and 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 subarctic to tropical. The family often forms the dominant component of boreal, coastal, and montane forests. One species, Pinus merkusii, grows just south of the equator in Southeast Asia. Major centres of diversity are found in the mountains of southwest China, Mexico, central Japan, and California.
Description The members of the family Pinaceae are trees (rarely shrubs) growing from 2 to 100 metres (7 to 300 feet) tall, mostly evergreen (except the deciduous Larix and Pseudolarix), resinous, monoecious, with subopposite or whorled branches, and spirally arranged, linear (needle-like) leaves. The embryos of Pinaceae have three to 24 cotyledons. The female cones are large and usually woody, 2–60 centimetres (1–24 inches) long, with numerous spirally arranged scales, and two winged seeds on each scale. The male cones are small, 0.5–6 cm (1⁄4–2+1⁄4 in) 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 their environments over time. All Pinaceae with seeds weighing less than 90 milligrams are seemingly adapted for wind dispersal. Pines having seeds larger than 100 mg 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. Boreal conifers have multiple adaptations to survive winters, including the tree's conical shape to shed snow, strong tracheid vessels to tolerate ice pressure, and a waxy covering on the needle leaves to minimise water loss.
Evolution
Fossil history The Pinaceae diverged from other conifer groups during the late Carboniferous ~313 million years ago. Various possible stem-group relatives have been reported from as early as the Late Permian (Lopingian) The extinct conifer cone genus Schizolepidopsis likely represent stem-group members of the Pinaceae, the first good records of which are in the Middle-Late Triassic, with abundant records during the Jurassic across Eurasia. The oldest crown group (descendant of the last common ancestor of all living species) member of Pinaceae is the cone Eathiestrobus, known from the Upper Jurassic (lower Kimmeridgian, 157.3-154.7 million years ago) of Scotland, which likely belongs to the pinoid grouping of the family. Pinaceae rapidly radiated during the Early Cretaceous. Members of the modern genera Pinus (pines), Picea (spruce), and Cedrus (cedar) first appear during the Early Cretaceous. The extinct Cretaceous genera Pseudoaraucaria and Obirastrobus appear to be members of Abietoideae, while Pityostrobus appears to be non-monophyletic, containing many disparately related members of Pinaceae. While Pinaceae, and indeed both of its subfamilies, substantially predate the break up of the super-continent Pangea, its distribution was limited to northern Laurasia. During the Cenozoic, Pinaceae had higher rates of species turnover than Southern Hemisphere conifers, thought to be driven by range shifts in response to glacial cycle.
Phylogeny Molecular studies show that Gnetophyta is the sister group to the Pinaceae, the lineages having diverged during the early-mid Carboniferous. This is known as the "gnepine" hypothesis. The Abietoideae and the Pinoideae diverged in the Jurassic. Pineae and Lariceae diverged in the Late Jurassic, while the Abieteae and Pseudolariceae diverged in the Cretaceous. A transcriptomic analysis in 2018 divided the Pinaceae into two clades, which have since been considered the two subfamilies Abietoideae and Pinoideae.
A study by J. D. Lockwood and colleagues in 2013 produced a broadly similar phylogeny, but with different placements for Pseudolarix and Cathaya. In this scheme, Pseudolariceae is subsumed by Abieteae.
Taxonomic history Classification of the subfamilies and genera of Pinaceae 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. In 1891, Van Tieghem divided the family into two subfamilies, using the number and position of resin canals in the primary vascular region of the young taproot as the primary consideration. In 1910, Friedrich Vierhapper divided the family into two tribes based on the occurrence and type of long–short shoot dimorphism. In 1976, Charles Miller divided the subfamilies and genera based on the consideration of features of ovulate cone anatomy among extant and fossil members of the family.
For example, Price (1987) classified the Pinaceae into 11 genera, grouped into four subfamilies, based on the microscopical anatomy and the morphology of the cones, pollen, wood, seeds, and leaves:
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