Laricoideae

Laricoideae
Subalpine Larch in Wenatchee National Forest, Washington State, U.S.
Scientific classification
Kingdom:Plantae
Division:Pinophyta
Class:Pinopsida
Order:Pinales
Family:Pinaceae
Subfamily:Laricoideae
(Rendle) Pilg. & Melch. (1954)
Genera

The Laricoideae are a subfamily of the Pinaceae, in turn a family of Pinophyta division. They take their name from the genus Larix (larches), which contains most of the species in the genus and is one of two genera in the pine family that are deciduous (together with Pseudolarix, which belongs to a different subfamily, the Abietoideae). Three genera (Larix, Pseudotsuga and Cathaya) are currently assigned to this subfamily and its members can be found only in Northern Hemisphere[1] at high or medium latitudes and altitudes.

Description

The species of the subfamily Laricoideae are evergreen or deciduous trees that can reach the greater heights between the Pinaceae family (100 meters with Pseudotsuga menziesii). The leaves are needle-like[1] and have primary stomatal bands abaxial (below the phloem vessels) only. All members are monoecious trees, with separate sexes on the same plant but in different reproductive structures. The annual seed cones have no distinct umbo and the scales show a broad base concealing the seeds fully from abaxial view. These last are whitish and firmly fixed to the seedwing (the wing holds the seed tightly in a cup). Furthermore, among the distinctive features of this group, we have the micropylar fluid of the strobilus absent, no resin vesicles on the seeds[1] and the presence, in the vascular cylinder of the young root, of two characteristic resiniferous canals.

Taxonomy

The subfamily Laricoideae, comprising its members, was described with the current name by Robert Knud Friedrich Pilger and Hans Melchior in late 1954[2] and subsequently modified by other authors. Before that, the genera Larix, Pseudotsuga and Cedrus were gathered in a provisional subfamily called Laricinae, described by Melchior and Werdermann in 1954 (...trees that have both short and long shoots, monomorphic leaves, and strobili borne on the short shoots...) and rechristened immediately after with the current term. The grouping in this form was confirmed by Hart (1987) through cladistic analysis, but already in 1988 Frankis replaced Cedrus with Cathaya (a genus described for the first time in 1962) in a new classification that saw Larix as a distinct twin group compared to Cathaya-Pseudotsuga. Historically the Laricoideae were the subfamily of the Pinaceae comprising the trees with needles inserted both on the macroblasts and on the brachiblasts; for this reason in the past they have been also included in it the genera Pseudolarix (for a short time) and Cedrus, now eliminated after the most recent systematic updates developed on the basis of molecular genetic phylogeny, reproductive morphologies, chromosome numbers and immunology. Currently, based on these studies, result three genera in the subfamily Laricoideae, of which one is monotypic, that is it consists of only one species:[1]

  • Larix Mill. - Larches are the genus type of this subfamily. Deciduous trees, they live in cold climates at high altitude in the mountains of temperate-cool zones or at high latitudes. They are found in North America, Central Europe and Northern Asia (Russia, Japan, China).
  • Pseudotsuga Carrière - Douglas-firs are medium to extremely large trees and often resemble morphologically as species of Abies or Tsuga. Have cones pendulous with persistent scales and three-pointed bract sticking out between scales. They are found in North America and Eastern Asia, where they can reach 100 m in height (Pseudotsuga menziesii).
  • Cathaya Chun & Kuang - Monotypical genus with the only species Cathaya argyrophylla. The leaves are needle-like, evergreen, 2.5–5 cm long with ciliate margins when young; they grow in spiral patterns around sprig. Cones 3–5 cm long with 15-20 scales, each scale bearing two winged seeds. This plant grows in southern China, in provinces of Guangxi, Guizhou, Hunan and southeast Sichuan on steep and narrow mountain slopes at 950–1800 m altitude.

Within the subfamily the genera Larix and Pseudotsuga are more closely related to each other than Cathaya. This evidence is demonstrated by numerous biological similarities between the larches and the Douglas-firs including wood anatomy, immunology of seed protein and the absence of the two air sacs in the pollen, typical instead of the Pinaceae. The biological and morphological similarities between the pollen grains of the genera Larix and Pseudotsuga however do not stop here[3] and include other aspects as: granule not buoyant, atectate, with exine granular, pollination drop containing xylose[4] and the presence of an exine shed during microgametophyte germination. Doyle and O'Leary[3] (1935) furthermore described the pollination very similar in Larix and Pseudotsuga where the pollen, which lacks air sacs, lands on an almost stigmatic extension of the integument, the margins of which tend to inroll. The contact with the nucellus may (Larix) or may not (Pseudotsuga) be needed for pollen tubes to develop, but the mechanism is almost analogous. The time from pollination to fertilization in these two genera may be over a year and pollen germination can take months (Little et al., 2014).[3]

Price et al. he supposed in 1977 that the Laricoideae were a subfamily sister of the Abietoideae rather than the Pinoideae - Piceoideae group and this version was confirmed by Hart (1987), Frankis (1988), Farjon (1990), Wang et al. (2000) and Gernandt et al. (2008).

Revisions

According to the latest research still in progress,[5] the genus Cathaya would be attributed to the grouping of pines (subfamily Pinoideae), leaving therefore only Larix and Pseudotsuga to forming the subfamily Laricoideae. Furthermore, studying the mitochondrial rps3 gene, Ran et al.[3] (2010) found that Larix and Pseudotsuga are evolutionarily sister genera to all other Pinaceae, thus highlighting a different (parallel) origin with respect to other species. This version, that would find evidence in genetics, however is not universally accepted[1] and many botanics, researchers and scientists still use the previous classification waiting for further developments.

References

  1. 1 2 3 4 5 Gymnosperm Database.
  2. ↑ "Subfamily Laricoideae (Rendle) Pilger & Melchior". BioLib. Retrieved 2013-05-19.
  3. 1 2 3 4 Rudolphi, F. (2018-01-05). "Pinaceae". In Stephens, P. F. Angiosperm Phylogeny Website, Version 14. Missouri Botanical Garden. Retrieved 2018-01-05.
  4. ↑ Nepi, M.; von Aderkas, P.; Wagner, R.; Mugnaini, S.; Coulter, A.; Pacini, E. (2009). "Nectar and pollination drops: how different are they?". Annals of Botany. 104 (2): 205–219. doi:10.1093/aob/mcp124. PMC 2710891.
  5. ↑ Lin, C. P.; Huang, J. P.; Wu, C. S.; Hsu, C. Y.; Chaw, S. M. (2010). "Comparative Chloroplast Genomics Reveals the Evolution of Pinaceae Genera and Subfamilies". Genome Biology and Evolution. 2: 504–517. doi:10.1093/gbe/evq036. PMC 2997556.

Bibliography

  • Earle, Christopher J., ed. (2018). "Pinaceae". The Gymnosperm Database. Retrieved 2013-05-19.
  • Lin, C. P; Huang, J. P; Wu, C. S; Hsu, C. Y; Chaw, S. M (2010). "Comparative Chloroplast Genomics Reveals the Evolution of Pinaceae Genera and Subfamilies". Genome Biology and Evolution. 2: 504–517. doi:10.1093/gbe/evq036. PMC 2997556.
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