9. Equisetum Laevigatum A. Br. Smooth Scouring-Rush

Fig. 97

Equisetum laevigatum A. Br.; Engelm. Amer. Journ. Sci. 46: 87. 1844.

Stems 1°-5° high, simple or little branched, pale green, annual or persistent, 14-30-furrowed, the ridges almost smooth. Sheaths elongated and enlarged upward, marked with a black girdle at the base of the mostly deciduous, white-margined teeth and rarely also at their bases; ridges of the sheath with a faint central carina and sometimes with faint short lateral ones; stomata arranged in single series; central cavity very large, the wall of the stem very thin, spikes pointed.

Along streams and rivers, especially in clay soil, Ontario to New Jersey, North Carolina, Louisiana, British Columbia and the Mexican border. May-June.

10. Equisetum Variegatum Schleich. Variegated Equisetum

Fig. 98

Equisetum variegatum Schleich. Cat. PI. Helvet. 27. 1807.

Stems slender, perennial, evergreen, 6'-18' long, rough, usually simple from a branched base, commonly tufted, 5-10-furrowed, the stomata borne in regular rows.. Sheaths campanulate, distinctly 4-cari-nate, green, variegated with black above, the median furrow deep and excurrent to the teeth and downward to the ridges of the stem, the teeth 5-10, each tipped with a decidugus bristle; central cavity small, rarely wanting.

Labrador and Greenland to Alaska, south to Con-neticut, western New York, Nebraska and Nevada. Also in Europe and Asia. Consists of several races. May-June.

11. Equisetum Scirpoides Michx. Sedgelike Equisetum

Fig. 99

Equisetum scirpoides Michx. Fl. Bor. Am. 2: 281. 1803.

Stems perennial, evergreen, very slender or filiform, 3'-6' long, somewhat rough, flexuous and curving, growing in slender tufts, mostly 6-furrowed with acute ridges, simple or branching from near the base. Sheaths 3-toothed, distinctly 4-carinate, the central furrow broad, the lateral narrow, the bristly teeth rather persistent; central cavity entirely wanting.

On moist or wet wooded banks, Labrador to Alaska, south to Pennsylvania, Illinois and British Columbia. Also in Europe and Asia. May-June.