The Pinaceae (), or pine family, are conifer trees or shrubs, including many of the well-known conifers of commercial importance such as Cedrus, , Tsuga, piñons,
, and . The family is included in the order Pinales, formerly known as Coniferales. Pinaceae have distinctive cones with woody scales bearing typically two Ovule, and are supported as monophyletic by both morphological trait and genetic analysis.
Description
Members of the family Pinaceae are
(rarely
) growing from tall, mostly
evergreen (except the
deciduous Larix and
Pseudolarix),
,
monoecious, with subopposite or whorled branches, and spirally arranged, linear (needle-like) leaves.
The embryos of Pinaceae have three to 24
.
The female conifer cone are large and usually woody, long, with numerous spirally arranged scales, and two winged on each scale. The male cones are small, 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.
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".
File:Floral Morphology and Anatomy of Picea sp. (Spruce).jpg|Floral Morphology and Anatomy of Picea sp. (Spruce)
File:Vagamon Pine Forest.jpg|Cultivated pine forest in Western Ghats, India
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:
-
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.
Evolutionary 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 all of its subfamilies, substantially predate the break up of the super-continent
Pangaea, 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 cycles.
Defense mechanisms
External stresses on plants have the ability to change the structure and composition of
Forest ecology. Common external stress that
Pinaceae experience are
herbivore and
pathogen attack which often leads to tree death.
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.
have the ability to up-regulate a combination of constitutive mechanical and
Chemical defense 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.[Franceschi, 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.] Constitutive and induced defenses are both found in the bark.
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
Phenols and resins.
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.
One of the common secondary compounds used by
Pinaceae are phenolics or polyphenols. These secondary compounds are preserved in
of polyphenolic
Parenchyma (PP) in the
Phloem.
Induced defenses
Induced defense responses need to be activated by certain cues, such as herbivore damage or other biotic signals.
A common induced defense mechanism used by Pinaceae is resins.
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.
Methyl jasmonate is known to be able to induce defense responses in the stems of multiple
Pinaceae species.
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.
File:Pinceae_Bishop_pine_prickle_cone_pine_pinus_muricata.jpg | Close up of bishop pine cones
File:Pinaceae_Knobcone_Pine_Pinus_attenuata.jpg | Knobcone pine cone
External links
