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The arbol del Tule, one of the largest trees in the world [C.J. Earle, 2005.02].

 

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Taxodium

Richard 1810

Common names

Baldcypress, swamp cypress.

Taxonomic notes

A genus generally assigned two species, though their chief difference is linguistic—one occurs in a country speaking English, the other, Spanish. They are:

Synonymy: Schubertia Mirbel 1812, Cuprespinnata J. Nelson 1866 (Farjon 2005).

The two species show only very minor differences in cuticle morphology, cone size and deciduous phenology. In accordance with the species concept as usually applied among conifers, they could be treated as subspecies or even varieties of a single species. However, since one species is the national tree of Mexico and the other has been a popular timber and ornamental tree for over 300 years, it would serve little purpose to attempt to combine the two taxa. T. distichum includes two varieties, which are also sometimes segregated as distinct species but which are sympatric throughout almost the entire range and which are based on several differences that are environmentally determined (Watson 1985); thus they are not really even defensible as subspecies, let alone distinct species. See Farjon (2005) for a detailed discussion of this issue.

A variety of morphological and genetic studies (the main ones are discussed under Cupressaceae) have established that this genus is a sister to Glyptostrobus and, slightly less closely, to Cryptomeria. This close similarity was early noted by Endlicher (1847) when he described Glyptostrobus and was later elaborated by studies of chloroplast and ribosomal DNA (Brunsfeld et al. 1994, Gadek et al. 2000, Kusumi et al. 2000) and seed cone development (Takaso and Tomlinson 1990, Farjon and Garcia 2005).

Description

"Trees deciduous or evergreen. Branchlets terete. Lateral roots commonly producing erect, irregularly conic to rounded "knees" in periodically flooded habitats. Leaves alternate, in 2 ranks or not. Adult leaves divergent to strongly appressed, linear or linear-lanceolate to deltate, generally flattened, free portion to ca. 17 mm; abaxial glands absent. Pollen cones with 10-20 sporophylls, each sporophyll with 2-10 pollen sacs. The pollen cones are usually borne at the base of alternate leaves, forming pendent axillary panicles; they occur less commonly singly or in racemes. Seed cones maturing and shattering in 1 season, nearly globose; scales falling early, 5-10, valvate, ± peltate, thin and woody. Seeds (1-)2 per scale, irregularly 3-angled, wingless; cotyledons 4-9. x = 11" (Watson 1993). The two species may be distinguished as follows (Farjon 2005):

Leaf stomata most abundant on the abaxial side, in broader bands than on adaxial side; mature seed cones mostly 20-35 mm long. T. distichum
Leaf stomata about equally abundant on both sides; mature seed cones mostly 14-25 mm long. T. mucronatum

Distribution and Ecology

Southern US, Mexico and Guatemala (Watson 1993), in riparian and wetland habitats.

Big tree

See T. mucronatum.

Oldest

T. distichum (1,622 years).

Dendrochronology

See T. distichum.

Ethnobotany

See the species descriptions.

Observations

See the species descriptions.

Remarks

The name is combined from Taxus, the generic name of yew, and the Greek root -oides, "like" (Watson 1993), presumably in reference to the foliage.

Both species of Taxodium at least occasionally produce "knees," also sometimes called "pneumatophores," which are wooden growths that come off the root system and stick up into the air, sometimes to a height of a meter, resembling nothing so much as woody stalagmites. They are typically associated with trees growing in saturated anoxic soils and they are sometimes hollow, but their bark does not develop stomata, lenticels, aerenchyma, or any of the other structures commonly associated with plants that achieve gas exchange through hollow roots. They do contain high concentrations of starch and thus may have a food storage function, but this also has not been shown (Farjon 2005). Their real function remains a mystery.

Citations

Farjon, A. and S.O. Garcia. 2005. The early development of ovuliferous cones in Cupressaceae s. lat -- A survey of the genera. Pages 27-46 (Chapter 4) in Farjon (2005).

Kusumi, J., Y. Tsumura, H. Yoshimaru and H. Tachida. 2000. Phylogenetic relationships in Taxodiaceae and Cupressaceae sensu stricto based on matK gene, ch/L gene, trnL-trn-F IGS region, and trnL intron sequences. American Journal of Botany 87(10): 1480-1488.

Takaso, T. and P.B. Tomlinson. 1990. Cone and ovule ontogeny in Taxodium and Glyptostrobus (Taxodiaceae - Coniferales). Botanical Journal of the Linnaean Society 109: 15-37.

Watson, F. D. 1985. The nomenclature of pondcypress and baldcypress. Taxon 34:506-509.

See also

Last Modified 2012-12-01