Calamites

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Calamites is a genus of extinct arborescent (tree-like) horsetails to which the modern horsetails (genus Equisetum) are closely related. Unlike their herbaceous modern cousins, these plants were medium-sized trees, growing to a height of 10 meters (31 feet). They were persistant minor component of coal swamps of the Carboniferous period.

Anatomy

The trunks of Calamites had a distinctive segmented, bamboo-like appearance and vertical ribbing. The branches, leaves and cones were all borne in whorls. The leaves were needle-shaped, with up to 25 per whorl.

Their trunks produced secondary xylem, meaning they were made of wood. The vascular cambium of Calamites was unifacial, producing secondary xylem towards the stem center, but not secondary phloem.

The stems of modern horsetails are typically hollow or contain numerous elongated air-filled sacs. Calamites was similar in that its trunk and stems were hollow, like wooden tubes. When these trunks buckled and broke, they could fill with sediment. This is the reason pith casts of the inside of Calamites stems are so common as fossils.

Reproduction

Calamites reproduced by means of spores, which were produced in small sacs organized into cones. They also known to have possesed massive, underground rhizomes, which allowed for the production of clones of one tree. This is the only group of trees of their period known to have a clonal habit. This type of asexual reproduction would allow them to spread quickly into new territory, in addition to aiding in anchoring them firmly in the unstable ground along rivers and in newly deposited delta sediments. The rhizomes of Calamites look quite similar to the stems in most cases, but have nodes that get progressively closer together as they get out approach the apical area (the growth tip that spreads outward through the soil).

Different forms

Calamites come in a variety of different "form genera". One type, Calamites suckowi, is distinguishable from other Calamites forms by its prominent, swollen nodes and relatively wide-spaced longitudinal ribs. Another example, Calamites cisti, has much smaller nodes and the ribs are typically closer together.

In addition, the distance between successive node lines on a Calamites suckowi specimen is typically much wider than the diameter. In other forms like Calamites cisti, the opposite is true or the specimen is just slightly wider than the diameter.

Extiction and classification

The genus Calamites has been placed in the plant division Equisetophyta (formerly known as Sphenophyta) and family Calamitaceae. They finally became extinct in the Lower Permian, a time which, however, also saw the origin of the family Equisetaceae, to which the only living sphenophyte genus Equisetum belongs.

See also

• Archaeopteris

References

• How large are the giant horsetails?
• Sphenophyta: Fossil Record
• Stewart, W. N. Paleobotany and the Evolution of Plants. Cambridge University Press, Cambridge (1983).
• Davis, Paul and Kenrick, Paul. Fossil Plants. Smithsonian Books (in association with the Natural History Museum of London), Washington, D.C. (2004). ISBN 1588341569