Taxodium

Taxodium

Taxodium is a genus of one to three species (depending on taxonomic opinion) of extremely flood-tolerant conifers in the cypress family, Cupressaceae. Within the family, Taxodium is most closely related to Chinese Swamp Cypress (Glyptostrobus pensilis) and Sugi (Cryptomeria japonica).

Species of Taxodium occur in the southern part of the North American continent and are deciduous in the north and semi-evergreen to evergreen in the south. They are large trees, reaching 100-150 feet tall (30-45 m) and 2-3 m (exceptionally 11 m) trunk diameter. The needle-like leaves, 0.5-2 cm long, are borne spirally on the shoots, twisted at the base so as to appear in two flat rows on either side of the shoot. The cones are globose, 2-3.5 cm diameter, with 10-25 scales, each scale with 1-2 seeds; they are mature in 7-9 months after pollination, when they disintegrate to release the seeds. The male (pollen) cones are produced in pendulous racemes, and shed their pollen in early spring.

Species

The three taxa of Taxodium are treated here as distinct species, though some botanists treat them in just one or two species, with the others considered as varieties of the first described. The three are distinct in ecology, growing in different environments, but hybridise where they meet.

The most familiar species in the genus is the Bald Cypress, native to much of the southeastern United States, from Delaware to Texas and inland up the Mississippi River to southern Indiana. It occurs mainly along rivers with silt-rich flood deposits.

The Pond Cypress occurs within the range of Bald Cypress, but only on the southeastern coastal plain from North Carolina to Louisiana. It occurs in still blackwater rivers, ponds and swamps without silt-rich flood deposits.

The Montezuma Cypress occurs from the Rio Grande south to the highlands of southern Mexico, and differs from the other two species in being substantially evergreen. A specimen at Santa Maria del Tule in Oaxaca, the Árbol del Tule, is 43 m tall and has the greatest trunk thickness of any living tree, 11.42 m in diameter. It is a riparian tree, occurring on the banks of streams and rivers, not in swamps like the Bald and Pond cypress.

Uses

The trees are especially prized for their wood, of which the heartwood is extremely rot and termite resistant, with the notable exception of the host-specific Pecky Rot fungus (Stereum taxodii), which causes some damaged trees to become hollow and thus useless for timber. "A biochemical called cypressene is believed to act as a natural preservative in the heartwood, but it takes many decades to build up in the wood, making lumber cut from old-growth trees much more resistant to decay than lumber from younger trees". - Sternberg, G., Native Trees for North American Landscapes pp. 476. Bald Cypress wood was much used in former days in southeastern US for shingles. The shredded bark of these trees is used as a mulch, although the current harvest rate for this product is not sustainable and is causing substantial environmental damage especially in the south where cutting boundaries are not being followed.

Evolution

In earth's history Taxodium was widespread. It is known since the Jurassic and can be found as fossil e.g. in layers from Tertiary times.

External links and references

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