The Laricoideae are a subfamily of the Pinaceae, a Pinophyta phylum family. They take their name from the genus Larix (larches), which contains inside most of the species of the Cultivar group and is one of only two deciduous genera of the Pinaceae (together with Pseudolarix, which however belongs to a different subfamily, the Abietoideae). Ecologically important trees, the Laricoideae form pure or mixed forest associations often dominant in the in which they are present, thanks also to their biological adaptations to natural disturbances, to reproductive strategies put in place and high average longevity of the individuals. Currently are assigned to this subfamily three genera ( Larix, Pseudotsuga and Cathaya) and its members can be found only in Northern Hemisphere. The various species live for the most part in temperate or cold climates and are the more northerly conifers; some constitute an important source of timber and non-timber forest products.
Description
The
species of the
subfamily Laricoideae are
evergreen or
deciduous trees that can reach the greater heights in the
Pinaceae family (over 100 meters with
Pseudotsuga menziesii var. menziesii). The
leaves are needle-like and have primary stomatal bands only on the abaxial surface (below the
phloem vessels). All members are
monoecious, with separate sexes on the same
plant but in different reproductive structures. The annual
seed cones (
strobili) have no distinct umbo and the scales show a broad base which, at observation, completely hides the
seeds from the abaxial view. These last are whitish and firmly fixed to the wing (this thin membrane also keeps the
seed well attached to the scale during maturation); furthermore, among the typical distinctive features of the group, we have the micropylar fluid of the
strobilus absent, no
resin vesicles on the
seeds and the presence, in the vascular cylinder of the young
root, of two characteristic small resiniferous canals. The bark and the
wood of the genera
Larix and
Pseudotsuga have a similar
anatomy and morphology: the reddish color of the
heartwood and the white-yellowish of the sapwood, the high
specific weight compared to other
conifers, the distribution of
latewood and
earlywood, the presence of resiniferous channels and their localization in the tissuets, the
molecules that form the
resin and extractives, the chemical, physical and mechanical properties as well as the class of resistance to the attack of
pathogens such as
fungi and
insects are a clue of a common ancestral origin. Similar between the two genera are also some aspects of the phenology, the degree of shade tolerance, the fire-resistant marbled bark and the appearance of the young shoots.
Taxonomy
The
subfamily Laricoideae was described with the actual name by Robert Knud Friedrich Pilger and
Hans Melchior in late 1954
and subsequently modified by other authors in the course of time as regards the
taxon of belonging. Before that, the genera
Larix,
Pseudotsuga and
Cedrus were gathered in a provisional
subfamily called
Laricinae, defined for the first time by Melchior and Werdermann always 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 (now obsolete) 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 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, subsequently eliminated following the most recent systematic updates developed on the basis of molecular genetic phylogeny, reproductive morphology, chromosome numbers and immunology. Currently, based on these studies, there are three genera in the subfamily Laricoideae, of which one of which is monotypic as it consists of only one species:
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Pseudotsuga macrocarpa (Vasey) Heinrich Mayr – Bigcone Douglas-fir, spontaneous in mountains of Southern California.
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Douglas fir (Mirb.) Franco - Western North America from Central British Columbia to Mexico (Oaxaca):
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Pseudotsuga menziesii var. menziesii – Coast Douglas-fir
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Pseudotsuga menziesii var. glauca (Ludwig Beissner) Franco – Rocky Mountain Douglas-fir
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Pseudotsuga menziesii var. lindleyana (Benedikt Roezl) Carrière – Mexican Douglas-fir
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Pseudotsuga brevifolia W.C.Cheng & L.K.Fu – Short-leaf Chinese Douglas-fir
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Pseudotsuga forrestii Craib – Yunnan Douglas-fir
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Pseudotsuga japonica (Shiras.) Beissn. – Japanese Douglas-fir
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Pseudotsuga sinensis Dode – Chinese Douglas-fir:
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Pseudotsuga sinensis var. sinensis
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Pseudotsuga sinensis var. wilsoniana – Taiwan Douglas-fir
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Pseudotsuga sinensis var. gaussenii
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Cathaya argyrophylla Chun & Kuang
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Within the subfamily the genera Larix and Pseudotsuga are more closely correlated to each other ( Sister group) than Cathaya. This evidence is demonstrated by numerous biological and macro-micro morphological similarities between the Larix and the Pseudotsuga including, but not only, a various tissues common anatomy, immunology of seed protein and the absence of the two air sacs in the pollen, typicals instead of the other Pinaceae. The similarities between the pollen grains of the genera Larix and Pseudotsuga however do not stop here
Price et al. he supposed in 1977 that the Laricoideae were a subfamily Sister group 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), although it has not yet found application in the literature.
Dichotomous key
The
dichotomous key to recognizing the
genera included to the
subfamily Laricoideae is relatively simple, since only three of them belong to it and one of these is
deciduous. Below is reported the taxonomic identification scheme in the form of a table:
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1. Laricoideae (includes Larix, Pseudotsuga and Cathaya): 2
- 2. Deciduous trees............................ Larix
- 2. Evergreen trees: 3
- : 3. Medium to extremely large trees; often resemble species of Abies or Tsuga; Conifer cone pendulous, persistent scales, three-pointed bract sticking out between scales............................ Pseudotsuga
- : 3. Leaves needle-like, 2.5-5 cm long, ciliate margins when young, grow in spiral patterns around stem; Conifer cone 3-5 cm long, 15-20 scales, each scale bearing two winged seeds............................ Cathaya argyrophylla
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Revisions and research
According to the latest research still in progress,
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. (2010)
found that
Larix and
Pseudotsuga are evolutionarily
Sister group to all other
Pinaceae, highlighting a different (sub-parallel) origin compared than the remaining
species. Spellenberg, Earle and Nelson (2014)
report that the
Larix and
Pseudotsuga evolved from the
Pinaceae 135 million years ago and they kept a common
ancestor until 7 million years ago, thus forming a divided and closely related taxonomic line between them compared to the rest of the group, while maintaining a strong degree of kinship with it. For Wang et al. (2000),
instead,
Pseudotsuga differentiated himself from
Larix in Western
North America about 65 million years ago, in an era between the late
Cretaceous and the
Paleocene. These revisions and interactions, which would find evidence in
genetics, however are not universally accepted and many botanics, researchers and scientists still use the previous classification waiting for further developments.
For other authors, finally, the subfamily Laricoideae would have no taxonomic dignity of its own, recognizing only two large multi-group clades (Pinoid and Abietoid
See also
Bibliography
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Pinaceae, Drawings and Descriptions of the Genera: Abies, Cedrus, Pseudolarix, Keteleeria, Nothotsuga, Tsuga, Cathaya, Pseudotsuga, Larix and Picea. Aljos Farjon. Koeltz Scientific Books, 1990 - 330 pages.
External links
