Terrestrial, to 1 m or more tall, erect or frequently arching and scandent; main stem articulate, glabrous or pubescent, sparsely leafy, the smaller stems inarticulate, more closely leafy, usually with short, stiff trichomes. Median leaves asymmetrical, sharply long-acuminate, decurrent at base, entire; lateral leaves +/- oblong, sharply acuminate, basifixed, 2-4 mm long, entire; leaves on main and secondary stems sparsely spaced, to 1 cm long, markedly auriculate. Cones terete to squarish at apices of ultimate branches; megaspores prominently white-ruffled. Shattuck 1158, Croat 16193. Rare, in ravines in the old forest. Standley reported S. conduplicata Spring., a synonym of S. arthritica. This report may have been based on a misdetermination of Shattuck 1158, which is this species.