The Pinaceae (/pɪˈneɪsiːˌiː,-siˌaɪ/), or pine family, are
conifer trees or shrubs, including many of the well-known conifers of commercial importance such as
cedars,
firs,
hemlocks,
piñons,
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.[1] They are the largest extant conifer family in species diversity, with between 220 and 250 species (depending on
taxonomic opinion) in 11 genera,[2] 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.[3] Major
centres of diversity are found in the mountains of
southwest China, Mexico, central Japan, and
California.
Description
Members of the family Pinaceae are
trees (rarely
shrubs) growing from 2 to 100 metres (7 to 300 feet) tall, mostly
evergreen (except the
deciduousLarix and Pseudolarix),
resinous,
monoecious, with subopposite or whorled branches, and spirally arranged, linear (needle-like) leaves.[2] 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.[4] Pinaceae that persist in areas where
tree squirrels are abundant do not seem to have evolved adaptations for bird dispersal.
Boreal conifers have many adaptions for winter. The narrow conical shape of northern conifers, and their downward-drooping limbs help them shed snow, and many of them seasonally alter their biochemistry to make them more resistant to freezing, called "hardening".
Classification
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. An 1891 publication 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 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 how the morphology has been used to classify Pinaceae.
The 11 genera are grouped into four subfamilies, based on the microscopical anatomy and the morphology of the cones, pollen, wood, seeds, and leaves:[5]
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
Piceoideae (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.
Subfamily
Laricoideae (Larix, Pseudotsuga, and Cathaya): 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.
Subfamily
Abietoideae (Abies, Cedrus, Pseudolarix, Keteleeria, Nothotsuga, and Tsuga): 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.
Phylogeny
A revised 2018 phylogeny places Cathaya as sister to the pines rather than in the Laricoidae subfamily with Larix and Pseudotsuga.
Multiple molecular studies indicate that in contrast to previous classifications placing it outside the conifers,
Gnetophyta may in fact be the sister group to the Pinaceae, with both lineages having diverged during the early-mid
Carboniferous. This is known as the "gnepine" hypothesis.[11][12]
Evolutionary history
Pinaceae is estimated to have diverged from other conifer groups during the late
Carboniferous ~313 million years ago.[13] 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.[14][15] 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,[16] which likely belongs to the pinoid grouping of the family.[17][15] Pinaceae rapidly radiated during the
Early Cretaceous.[13] Members of the modern genera Pinus (pines), Picea (spruce) and Cedrus (cedar) first appear during the Early Cretaceous.[18][19][20] 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.[17] While Pinaceae, and indeed all of its subfamilies, substantially predate the break up of the super-continent
Pangea, its distribution was limited to the 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 cycles.[21]
Defense mechanisms
External stresses on plants have the ability to change the structure and composition of
forest ecosystems. Common external stress that Pinaceae experience are
herbivore and
pathogen attack which often leads to tree death.[22] In order to combat these stresses, trees need to adapt or evolve defenses against these stresses. Pinaceae have evolved a myriad of mechanical and chemical defenses, or a combination of the two, in order to protect themselves against antagonists.[23]Pinaceae have the ability to up-regulate a combination of constitutive mechanical and
chemical strategies to further their defenses.[24]
Pinaceae defenses are prevalent in the bark of the trees. This part of the tree contributes a complex defensive boundary against external antagonists.[25]Constitutive and
induced defenses are both found in the bark.[25][26][27]
Constitutive defenses
Constitutive defenses are typically the first line of defenses used against antagonists and can include sclerified cells, lignified periderm cells, and secondary compounds such as
phenolics and resins.[28][25][26] Constitutive defenses are always expressed and offer immediate protection from invaders but could also be defeated by antagonists that have evolved adaptations to these defense mechanisms.[28][25] One of the common secondary compounds used by Pinaceae are phenolics or polyphenols. These secondary compounds are preserved in
vacuoles of polyphenolic
parenchyma cells (PP) in the
secondary phloem.[29][27]
Induced defenses
Induced defense responses need to be activated by certain cues, such as herbivore damage or other biotic signals.[28]
A common induced defense mechanism used by Pinaceae is resins.[30] Resins are also one of the primary defenses used against attack.[23] Resins are short term defenses that are composed of a complex combination of volatile
mono- (C10) and
sesquiterpenes (C15) and nonvolatile
diterpene resin acids (C20).[23][30] They are produced and stored in specialized secretory areas known as resin ducts, resin blisters, or resin cavities.[30] Resins have the ability to wash away, trap, fend off antagonists, and are also involved in wound sealing.[29] They are an effective defense mechanism because they have toxic and inhibitory effects on invaders, such as insects or pathogens.[31] Resins could have developed as an evolutionary defense against
bark beetle attacks.[30] One well researched resin present in Pinaceae is
oleoresin. Oleoresin had been found to be a valuable part of the
conifer defense mechanism against
biotic attacks.[31] They are found in
secretory tissues in tree stems, roots, and leaves.[31] Oleoresin is also needed in order to classify conifers.[31]
Active research: methyl jasmonate
The topic of defense mechanisms within family Pinaceae is a very active area of study with numerous studies being conducted. Many of these studies use
methyl jasmonate (MJ) as an antagonist.[26][27][32] Methyl jasmonate is known to be able to induce defense responses in the stems of multiple Pinaceae species.[26][32] It has been found that MJ stimulated the activation of PP cells and formation of xylem traumatic resin ducts (TD). These are structures that are involved in the release of phenolics and resins, both forms of defense mechanism.[26][27]
^Robert A. Price, Jeanine Olsen-Stojkovich & Jerold M. Lowenstein (1987). "Relationships among the genera of Pinaceae: an immunological comparison". Systematic Botany. 12 (1): 91–97.
doi:
10.2307/2419217.
JSTOR2419217.
^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.
doi:
10.3732/ajb.1100595.
PMID22491001.
^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 Genus Pinus from the Early Cretaceous of Yorkshire, United Kingdom". International Journal of Plant Sciences. 173 (8): 917–932.
doi:
10.1086/667228.
S2CID85402168.
^
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.