HORSETAIL FA^IILY 



41 



6. Equisetum kansanum Schaftn. 



Summer Scouring-rush. 



Fig. 86. 



Equtsctum kansanum Schaftn. Ohio Nat. 13: 21. 1912. 



Rhizome dull blackisli. naked except at the nodes. 

 Aerial stems annual, single or clustered, erect, usu- 

 ally unbranched, 30-90 cm. long, 2-8 mm. thick, light 

 green, 15-30-grooved, smooth or slightly roughened, 

 the ridges rounded, with or without cross-bands of 

 silica, a single row of stomata borne at each side; 

 central cavity about three-fourths the diameter of the 

 stem ; sheaths elongate, green, contracted at the base, 

 dilate upward, with a narrow black terminal band, 

 the constituent leaves keeled in their lower half or 

 two-thirds ; teeth partly deciduous, cohering in groups 

 by their whitish membranous borders, the persistent 

 triangular bases rigid, lilackish, shining, incurved at 

 the tips or not ; spikes sessile or short-exserted. 1-3 

 cm. long, oblong-ovoid, obtuse. 



Ravine banks and moist slopes, commonly in clay, Upjier 

 Sonoran and Transition Zones; British Columbia to Ontario, 

 south to southern California, Arizona, New Mexico, Missouri, 

 and Ohio. Type locality: Bloom Township, Clay County, 

 Kansas. 



2 

 "3" 



7. Equisetum variegatum Schleich. 

 Xorthern Scouring-rush. Fig. 87. 



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



Aerial stems usually perennial, erect or assur- 

 gent, clustered, naked or rarely branched, 15-60 cm. 

 long, 1.5-4 mm. thick, 5-12-angled, rough or smooth- 

 ish. the ridges grooved, bearing 2 lines of silica 

 tubercles ; central cavity about one-third to half the 

 diameter of the stem ; sheaths campanulate, green, 

 black or variegated with black above, the constitu- 

 ent leaves distinctly 4-angled, with a deep median 

 groove, this decurrent into the stem ridges and 

 excurrent to the teeth ; teeth mostly persistent, 

 ample, connivent by their broad, whitish, _ mem- 

 branous borders, the middle portion blackish or 

 dark brown, prolonged into a rough, long-attenuate, 

 usually deciduous tip; terminal sheath large, the 

 spike sessile, 5-10 mm. long, strongly apiculate. 



Wet meadows, bogs, and alluvial thickets. Boreal Region; 

 Alaska to Labrador, south to Oregon, Wyoming, and (Con- 

 necticut; Greenland; Eurasia. Type localit)-: Switzerland. 

 Several varieties are recognized. 



8. Equisetum scirpoides Michx. 

 Sedgelike Horsetail. Fig. 88. 



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



Aerial stems numerous (10-100), tufted, simple, or 

 slightly branched at the base, green, prostrate or laxly 

 ascending, filiform, about 1 mm. thick, flexuous, 5-15 

 (25) cm. long, solid at the center, 6-ribbed by the 

 very deep grooving of the 3 angles, the ribs with a 

 regular row of silica tubercles ; sheaths loose, becoming 

 black or dark brown, the 3 constituent leaves with a 

 very broad central groove and 2 lateral ones, thus 4- 

 carinate ; teeth 3, distinct, persistent, blackish with broad 

 white borders, the tips subulate, fragile; spikes 3-5 mm. 

 long, sessile or short-pedunculate. 



Low fields, swamps, and moist evergreen woods. Boreal Region; 

 Alaska to Labrador, south to Washington, Montana, Michigan, 

 Illinois, and Pennsylvania; Eurasia. Type locality: Canada. 



