Wednesday, May 20, 2009

Fossil of the Week

Horsetails (also known as bottle or scouring rushes) are a group of vascular plants that reproduce by spores rather than seeds. They date back to the Late Devonian (375 million years ago); only one genus (Equisetum) survives today. Their presence in the fossil record indicates a humid to wet habitat such as along rivers and lakes.The stems of horsetails are hollow, distinctively segmented and bamboo-like in appearance, and are adorned with vertical ribs. The branches and leaves are borne in whorls attached to the stem at nodes. The leaves can be borne directly on the stem or on delicate side branches identical in structure to the main stem. Fossil horsetails, unlike their modern cousins, were medium-sized trees, growing to more than 30 meters (100 feet) in height. They were common components of coal swamps of the Carboniferous Period.

Text by Paula Mikkelsen, Photo courtesy J. Casciano

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