by Nathaniel Lord Britton & Addison Brown

“ Ridges of the stem roughened with a single aeries of transversely oblong siliceous tubercles; sheaths short, nearly as broad as long, cylindric, appressed, marked with black girdles at the base, and at the bases of the dark caducous teeth; ridges of the sheath 3-carinate; branches when present occasionally fertile; spikes tipped with a rigid point. ”

“ Stems slender, rather stiff, evergreen, 2-4 high, with the stomata arranged in regular rows, rough, 8-34-furrowed, the ridges with two indistinct lines of tubercles, the central cavity large, from one-half to two-thirds the diameter; sheaths rather long, cylindric, marked with one or two black girdles, their ridges obscurely 4-carinate; teeth brown, membranous, soon deciduous; spikes pointed; stem rarely producing branches which are usually short and occasionally fertile; forms are sometimes found with longer sterile branches. ”

“ Spores all of the same size and shape, furnished with 2 narrow strap-like appendages attached at the middle, coiling around the spore when moist and spreading when dry and mature, in the form of a cross (elaters) . Epidermis impregnated with silica, rough. Prothallium on the surface of the ground, green, usually dioecious. ”