One of the major divisions (formerly known as Equisetophyta) of vascular plants that includes both living and fossil representatives. The three principal orders are Pseudoborniales (Devonian), Sphenophyllales (Devonian-Triassic), and Equisetales (Devonian-Recent); the Hyeniales (Devonian) may also be sphenophytes. See also Equisetales; Hyeniales; Pseudoborniales; Sphenophyllales.
All sphenophytes are characterized by axes with distinct nodes that produce whorls of small leaves or branches; branches often contain longitudinal ribs and furrows. Internally the stems of sphenophytes are characterized by longitudinally oriented canals, some of which functioned in gaseous exchange. Secondary tissues were produced in a few fossil forms. The reproductive organs of this group are loosely arranged strobili or cones consisting of a central axis bearing whorls of modified branches, each terminating in a recurved, thick-walled sporangium. Most sphenophytes produced one type of spore (homospory), although a few fossil forms were heterosporous.
Today all that remains of the sphenophytes is the genus Equisetum, commonly called the horsetail or scouring rush. Except in Australia and New Zealand, the members are worldwide in distribution and typically grow in damp habitats along the edges of streams, although some species are adapted to mesic conditions. A few species attain considerable size, but none of these produce secondary tissues. See also Embryobionta.
