Equisetum L.

Terrestrials or subaquatics of stream banks, often immersed for considerable periods, of moderate size. Rhizome creeping underground bearing roots at the nodes; aerial stems erect, terete, longitudinally grooved, stomata in the grooves, siliceous cells on the ridges, jointed, hollow with a large central hollow (centrum) surrounded by small vallecular canals beneath each grooved, and smaller carinal canals beneath each ridge, photosynthetic, the leaves reduced to persistent or deciduous scariose teeth in a single whorl on an entire sheath at each node, the stem unbranched or with 1 - many branches borne in a whorl beneath the nodal sheath; vascular bundles of a region of phloem flanked by 2 patches of xylem immediately outside each carinal canal, uniting to form a complete cylinder (a medullated protostele) at the nodes. Sporangia borne in groups of 5 - 10 on the underside of peltate, +/- hexagonal sporangiophores, aggregated into a compact ovoid or ellipsoid terminal strobilis. Spores round, green, with 4 coiled, elongate-spathulate bands (elater) with a common point of attachment, that uncoil and recoil with changes in humidity.

Species in Papuasia