The seeds and the rhizomes contain an abundance of starch, which renders them serviceable in some places for food.
Sudan is extracted partly from the roots of Landolphia or from the rhizomes of Landolphia Thollonii or Carpodinus lanceolatus.
The morphology of Stigmaria has been much discussed; possibly the main axes, which do not agree perfectly either with rhizomes or roots, may best be regarded as comparable with the rhizophores of Selaginellae; they have also been compared with the embryonic stem, or protocorm, of certain species of Lycopodium; the homologies of the appendages with the roots of recent Lycopods appear manifest.
The stems, long known from Australia and India as Vertebraria, have in recent years been proved to be the rhizomes of Glossopteris.
Represented by casts of Triassic age, Equisetites arenaceus and other species, probably possessed the power of secondary growth in thickness; the cones were of the modern type, and the rhizomes occasionally formed large underground tubers like those frequently met with in Equisetum arvense, E.