ThePinaceae, orpine family, areconifer trees or shrubs, including many of the well-known conifers of commercial importance such ascedars,firs,hemlocks,larches,pines, andspruces. The family is included in the orderPinales, formerly known asConiferales. Pinaceae have distinctive cones with woody scales bearing typically twoovules, and are supported asmonophyletic by bothmorphological trait and genetic analysis.[2] They are the largest extant conifer family in species diversity, with between 220 and 250 species (depending ontaxonomic opinion) in 11 genera,[3] and the second-largest (afterCupressaceae) in geographical range, found in most of theNorthern Hemisphere, with the majority of the species in temperate climates, but ranging from subarctic to tropical. The family often forms the dominant component ofboreal, coastal, andmontane forests. One species,Pinus merkusii, grows just south of theequator in Southeast Asia.[4] Majorcentres of diversity are found in the mountains ofsouthwest China, Mexico, central Japan, andCalifornia.
The members of the family Pinaceae aretrees (rarelyshrubs) growing from 2 to 100 metres (7 to 300 feet) tall, mostlyevergreen (except thedeciduousLarix andPseudolarix),resinous,monoecious, with subopposite or whorled branches, and spirally arranged, linear (needle-like) leaves.[3] The embryos of Pinaceae have three to 24cotyledons.
The femalecones are large and usually woody, 2–60 centimetres (1–24 inches) long, with numerous spirally arranged scales, and two wingedseeds 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 wheretree squirrels are abundant do not seem to have evolved adaptations for bird dispersal.[5]
Boreal conifers have multipleadaptations 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.[6]
The Pinaceae diverged from other conifer groups during the lateCarboniferous ~313 million years ago.[7] Various possiblestem-group relatives have been reported from as early as the LatePermian (Lopingian) The extinct conifer cone genusSchizolepidopsis likely represent stem-group members of the Pinaceae, the first good records of which are in the Middle-LateTriassic, with abundant records during theJurassic across Eurasia.[8][9] The oldestcrown group (descendant of the last common ancestor of all living species) member of Pinaceae is the coneEathiestrobus, known from the Upper Jurassic (lowerKimmeridgian, 157.3-154.7 million years ago) of Scotland,[10] which likely belongs to the pinoid grouping of the family.[11][9] Pinaceae rapidly radiated during theEarly Cretaceous.[7] Members of the modern generaPinus (pines),Picea (spruce), andCedrus (cedar) first appear during the Early Cretaceous.[12][13][14] The extinct Cretaceous generaPseudoaraucaria andObirastrobus appear to be members of Abietoideae, whilePityostrobus appears to be non-monophyletic, containing many disparately related members of Pinaceae.[11] While Pinaceae, and indeed all of its subfamilies, substantially predate the break up of the super-continentPangea, its distribution was limited to northernLaurasia. 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.
Molecular studies show thatGnetophyta is the sister group to the Pinaceae, the lineages having diverged during the early-midCarboniferous. This is known as the "gnepine" hypothesis.[15][16][17] 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.[18]
A study by J. D. Lockwood and colleagues in 2013 produced broadly similar results, but with different placements forPseudolarix andCathaya. In this scheme, Pseudolariceae is subsumed by Abieteae.[19]
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 ofresin 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.[20] 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.[21]
Cone features used in Pinaceae taxonomy
Immature 2nd-year cone ofPinus nigra, light brown umbo on green cone scales
Immature cone ofPicea abies, no umbo
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:[22]
SubfamilyPinoideae (Pinus): cones are biennial, rarely triennial, with each year's scale-growth distinct, forming an umbo on each scale, the cone scale base is broad, concealing the seeds fully fromabaxial (below thephloem vessels) view, the seed is without resin vesicles, the seed wing holds the seed in a pair of claws, leaves have primary stomatal bands adaxial (above the xylem) or equally on both surfaces.[22]
SubfamilyPiceoideae (Picea): cones are annual, without a distinct umbo, the cone scale base is broad, concealing the seeds fully from abaxial view, seed is without resin vesicles, blackish, the seed wing holds the seed loosely in a cup, leaves have primary stomatal bands adaxial (above the xylem) or equally on both surfaces.[22]
SubfamilyLaricoideae (Larix,Pseudotsuga, andCathaya): cones are annual, without a distinct umbo, the cone scale base is broad, concealing the seeds fully from abaxial view, the seed is without resin vesicles, whitish, the seed wing holds the seed tightly in a cup, leaves have primary stomatal bands abaxial only.[22]
SubfamilyAbietoideae (Abies,Cedrus,Pseudolarix,Keteleeria,Nothotsuga, andTsuga): cones are annual, without a distinct umbo, the cone scale base is narrow, with the seeds partly visible in abaxial view, the seed has resin vesicles, the seed wing holds the seed tightly in a cup, leaves have primary stomatal bands abaxial only.[22]
External stresses on plants have the ability to change the structure and composition offorest ecosystems. Common external stresses that Pinaceae experience areherbivore andpathogen attacks, which can kill trees.[23] In order to combat these stresses, trees need to adapt or evolve defenses against these stresses. Pinaceae have evolved myriad mechanical and chemical defenses, or a combination of the two, in order to protect themselves against antagonists.[24] Pinaceae have the ability to up-regulate a combination of constitutive mechanical andchemical strategies to further their defenses.[25]
Pinaceae defenses are prevalent in the bark of the trees. This part of the tree contributes a complex defensive boundary against external antagonists.[26]Constitutive andinduced defenses are both found in the bark.[26][27][28]
Constitutive defenses are typically the first line of defenses used against antagonists. These defenses include sclerified cells, lignified periderm cells, and secondary compounds such asphenolics and resins.[29][26][27] Constitutive defenses are always expressed and offer immediate protection from invaders but can be defeated by antagonists that have evolved adaptations to these defense mechanisms.[29][26] Common secondary compounds used by Pinaceae are phenolics or polyphenols. These are preserved invacuoles of polyphenolicparenchyma cells (PP) in thesecondary phloem.[30][28]
Induced defense responses need to be activated by certain cues, such as herbivore damage or other biotic signals.[29]
A common induced defense mechanism used by Pinaceae is resins.[31] Resins are also one of the primary defenses used against attack.[24] Resins are short term defenses that are composed of a complex combination of volatilemono- (C10) andsesquiterpenes (C15) and nonvolatilediterpene resin acids (C20).[24][31] They are produced and stored in specialized secretory areas known as resin ducts, resin blisters, or resin cavities.[31] Resins have the ability to wash away, trap, fend off antagonists, and are also involved in wound sealing.[30] They are an effective defense mechanism because they have toxic and inhibitory effects on invaders, such as insects or pathogens.[32] Resins could have developed as an evolutionary defense againstbark beetle attacks.[31] One well researched resin present in Pinaceae isoleoresin. Oleoresin had been found to be a valuable part of theconifer defense mechanism againstbiotic attacks. They are found insecretory tissues in tree stems, roots, and leaves.[32]
Many studies usemethyl jasmonate as an antagonist.[27][28][33] Methyl jasmonate induces defense responses in the stems of multiple Pinaceae species.[27][33] Methyl jasmonate stimulates the activation of PP cells and formation of xylem traumatic resin ducts (TD). These are involved in the release of phenolics and resins, both forms of defense mechanism.[27][28]
^Rothwell, Gar W.; Mapes, Gene; Stockey, Ruth A.; Hilton, Jason (April 2012). "The seed cone Eathiestrobus gen. nov.: Fossil evidence for a Jurassic origin of Pinaceae".American Journal of Botany.99 (4):708–720.Bibcode:2012AmJB...99..708R.doi:10.3732/ajb.1100595.PMID22491001.
^Blokhina, N. I.; Afonin, M. (2007). "Fossil wood Cedrus penzhinaensis sp. nov. (Pinaceae) from the Lower Cretaceous of north-western Kamchatka (Russia)".Acta Paleobotanica.47:379–389.S2CID54653621.
^Patricia E. Ryberg; Gar W. Rothwell; Ruth A. Stockey; Jason Hilton; Gene Mapes; James B. Riding (2012). "Reconsidering Relationships among Stem and Crown Group Pinaceae: Oldest Record of the GenusPinus from the Early Cretaceous of Yorkshire, United Kingdom".International Journal of Plant Sciences.173 (8):917–932.Bibcode:2012IJPlS.173..917R.doi:10.1086/667228.S2CID85402168.
^Gernandt, D.S.; Vining, T.F.; Campbell, C.S.; Piñero, D.; Liston, A. (August 1999).Molecular phylogeny of Pinaceae and Pinus(PDF). IV International Conifer Conference 615. pp. 107–114.
^abcdFranceschi, V. R., P. Krokene, T. Krekling, and E. Christiansen. 2000. Phloem parenchyma cells are involved in local and distance defense response to fungal inoculation or bark-beetle attack in Norway spruce (Pinaceae). American Journal of Botany 87:314-326.
^abcdNagy, Nina E.; Franceschi, Vincent R.; Solheim, Halvor; Krekling, Trygve; Christiansen, Erik (2000-03-01). "Wound-induced traumatic resin duct development in stems of Norway spruce (Pinaceae): anatomy and cytochemical traits".American Journal of Botany.87 (3):302–313.doi:10.2307/2656626.JSTOR2656626.PMID10718991.
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