Pinaceae

The members of the family Pinaceae are trees (rarely shrubs) growing from tall, mostly evergreen (except the deciduous Larix and Pseudolarix), resinous, monoecious, with subopposite or whorled branches, and spirally arranged, linear (needle-like) leaves. 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. File:496 Pinus silvestris.jpg|Features of Pinus sylvestris File:Vagamon Pine Forest.jpg|Cultivated pine forest in Western Ghats, India == 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. 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. 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. File:Ab plant 673.jpg|Immature 2nd-year cone of Pinus nigra, light brown umbo on green cone scales File:Norway Spruce cone.jpg|Immature cone of Picea 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: • Subfamily Pinoideae (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 from abaxial (below the phloem 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. • Subfamily Pinoideae (Cathaya, Larix, Picea, Pinus, and Pseudotsuga) • Subfamily Abietoideae (Abies, Cedrus, Pseudolarix, Keteleeria, Nothotsuga, and Tsuga) == Genera ==

Extant • Abies • Cedrus • Keteleeria • Nothotsuga • Pseudolarix • Tsuga • Pinus • Picea • Pseudotsuga • Cathaya • Larix Extinct • †Tsugaepollenites • †Abietipites • †Cedripites • †Schizolepidopsis • †Eathiestrobus • †Pesudoaraucaria • †Obirostrobus • †Pityostrobus == Defense mechanisms ==

External stresses on plants have the ability to change the structure and composition of forest ecosystems. Common external stresses that Pinaceae experience are herbivore and pathogen attacks, which can kill trees. 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. Pinaceae have the ability to up-regulate a combination of constitutive mechanical and chemical strategies to further their defenses. Pinaceae defenses are prevalent in the bark of the trees. This part of the tree contributes a complex defensive boundary against external antagonists. Constitutive and induced defenses are both found in the bark. Constitutive defenses Constitutive defenses are typically the first line of defenses used against antagonists. These defenses include sclerified cells, lignified periderm cells, and secondary compounds such as phenolics and resins. Resins are also one of the primary defenses used against attack. Resins could have developed as an evolutionary defense against bark beetle attacks. Methyl jasmonate induces defense responses in the stems of multiple Pinaceae species. 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. File:Pinceae_Bishop_pine_prickle_cone_pine_pinus_muricata.jpg | Bishop pine cones File:Pinaceae_Knobcone_Pine_Pinus_attenuata.jpg | Knobcone pine cone == References ==