Calamitales

an order of extinct plants with segmented stems, resembling giant horsetails.

Members of this order reached a height of 8-12 m and a diameter of 0.5-1 m. The stem consis ted of nodes and internodes. The nodes of the shoots had whorls of branches or simple linear leaves with one vein (the genera Annularia and Asterophyllites). The spore-bearing cones of Calamitales were composed of alternating fruiting and sterile leaves (sporangiophores). Calamitales differed anatomically from horsetails in having highly developed secondary wood; however, like horsetails, they had in their trunks a large cavity in place of the pith, which was destroyed early in development. The basic genus of Calamitales, Calamites, had three subgenera (Stylocaiamites, Calamitina, and Eucala-mites). Primitive Calamitales (Osterocalamites), which appeared at the end of the Devonian period and became extinct in the middle of the Carboniferous period, were replaced by Calamitales proper, which in turn disappeared during the Permian period. Calamitales reached their greatest distribution and dimensions in the tropical zone (the Euramerican paleofloral region), where they grew in lowlands and, 5; in swampy places.