an anatomic structure of the conducting cylinder, or stele, of the stem or root in plants of the division Lycopodiophyta. In contrast to the steles of other groups of plants, the plectostele has a spongy rather than a reticular structure. The xylem is distributed in sections impregnated in the phloem. In some species of Lycopodium the xylem is distributed in the shape of a cross (similar to an actinostele). The plectostele developed from the protostele, which is characteristic of the oldest terrestrial plants—psilophytes of the genus Rhynia and some extant ferns.