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Taxodium is a genus of one to three species (depending on taxonomic opinion) of extremely flood-tolerant conifers in the cypress family, Cupressaceae, one of several genera in the family commonly known as cypresses. 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 30_45 m tall 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 listed 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.
Bald Cypress The most familiar species is the Bald Cypress (Taxodium distichum), also known as Southern Cypress or Swamp Cypress, native to much of the southeastern United States, from Delaware to Texas and inland up the Mississippi River to southern Indiana. The northern limitations are not due to a lack of cold tolerance, but to specific reproductive requirements. The trees are called 'bald' because, unlike most other cypresses, they lose their leaves during the winter months.
Ancient Bald Cypress forests, with some trees over 1200 years old, once dominated swamps in the southeast US. The largest remaining stand of Bald Cypress is at Corkscrew Swamp Sanctuary, near Naples, Florida. These trees are around 500 years of age and some now exceed 40m (130 ft) in height. The Bald cypress occurs mainly along riparian (riverside) wetlands subject to periodic flooding by silt-rich 'brownwater' rivers.
Bald Cypresses growing in swamps have a peculiarity of growth called cypress knees. These are woody projections sent above the water from the roots. Their function is thought to be to provide oxygen to the roots that grow in the low dissolved oxygen (DO) waters typical of a swamp (see also mangroves, which have similar adaptations).
The Bald Cypress was designated the official state tree of Louisiana in 1963, and is considered by some to be a symbol of the southern swamps.
Pond Cypress The Pond Cypress (Taxodium ascendens or T. distichum var. imbricatum) is usually smaller than the Bald Cypress, and the bark is a lighter gray. The leaves are shorter, slenderer and are on shoots that tend to be erect rather than spreading. It occurs within the range of Bald Cypress, but only on the southeastern coastal plain from North Carolina to Louisiana. It differs in ecology, occurring mainly in still blackwater rivers, ponds and swamps without silt-rich flood deposits.
Montezuma Cypress The Montezuma Cypress (Taxodium mucronatum or T. distichum var. mucronatum) from the Rio Grande south to the highlands of southern Mexico differs from the other two species in being substantially evergreen. A specimen 43 m tall at Santa Maria del Tule in Oaxaca 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.
External links and references - Gymnosperm Database _ Taxodium (http://www.botanik.uni_bonn.de/conifers/cu/tax/index.htm)
- Corkscrew Swamp Sanctuary website (http://www.audubon.org/local/sanctuary/corkscrew/)
- National Audubon Society, undated. Corkscrew Swamp Sanctuary. A Companion Field Guide. Artype Inc., Ft. Meyers. 25 p.
- Sternberg, Guy, (2004) Native Trees for North American Landscapes pp. 476. Timber Press, Inc.
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