42 



EOUISETACEAE 



1 



5 



10: 120. 



9. Equisetum laevigatum A. Br. 

 Braiin's Scouring-rush. Fig. 89. 



Equisetum laevigatum A. Br. Am. Journ. Sci. 46: 87. 1S44. 



Equisetum hiemale intermedium A. A. Eaton, Fern Bull. 



1902. 



Equisetum intermedium Rydb. Fl. Rocky Mts. 1053. 191/. 



Aerial stems usually persisting 2 or more seasons, tufted, 

 erect, simple or at length sparingly branched, 30-120 cm. 

 long, 2-8 mm. thick, 20-30-angled, smoothish or rough, the 

 ridges bearing cross-bands of silica ; sheaths much longer 

 than broad, dilated upward, the lower 3 or 4 usually with 

 inferior and apical black rings, the others green, or com- 

 monly all the sheaths banded after the first year; leaves 

 centrally keeled below, narrowed upward, the brown- 

 spotted tips contracted and incurved with age, joined by 

 rather broad pale commissures; teeth thin, brownish, 

 flexuous, caducous to persistent, at first cohering in groups 

 by their pale transparent borders ; small stems and branches 

 usually very rough, the leaves centrally grooved, with sub- 

 persistent teeth ; spikes 1-2 cm. long, sharply apiculate. 



Damp alluvial thickets and sandy banks, chiefly in the Upper So- 

 noran Zone; British Columbia to southern California, east to New 

 York, Illinois, Missouri, and Texas. Type locality: near St. Louis, 

 Missouri. 



10. Equisetum praealtum Raf. 

 Prairie Scouring-rush. l*"ig. 90. 



Equisetum praealtum Raf. FI. Ludovic. 13. 1817. 

 Equisetum robustum A. Br.; Engelm. Am. Journ. Sci. 46: 88. 



1844. 



Aerial stems persisting several seasons, rigidly 

 erect, simple or at length branched, mostly 0.4-2 

 meters long, 4-12 mm. thick, 16-48-angled, very 

 rough, the ridges with irregular, strongly elevated 

 cross-bands of silica, the tips of these sometunes 

 more prominent ; sheaths a little longer than broad, 

 or not, cylindrical, tight, at maturity ashy in the 

 middle with a black basal band and a narrower 

 apical one, at length commonly deciduous in recurved 

 fragments ; leaves narrowly linear, sharply 3-carinate, 

 the central keel rarely grooved; teeth articulate, 

 brown centrally, subpersistent, cohering in groups; 

 branches variable, the sheaths with persistent teeth; 

 spikes oval, 1-2.5 cm. long, sharply apiculate. 



Moist, usually alluvial situations: British Columbia to 

 Quebec, southward nearly throughout the United States. 

 Type locality: Louisiana. 



3 



5 



11. Equisetum hiemale calif ornicum ]\Iilde. 

 Western Scouring-rush. 



Fig. 91. 



Equisetum hiemale califomicum Milde, Nov. Act. Acad. Caes. Leop. 

 Carol. Z2-: 517. 1867. 



Aerial stems persisting several seasons, rigidly erect, 



clustered, naked or at length rarely branched toward the 



apex, 0.5-2.5 mm. high, 5-15 mm. thick, 25-40-angled, 



rough, the ridges usually with 2 distinct rows of silica 



tubercles; sheaths as broad as long, cylindrical or slightly 



dilated above, variable in coloration, at maturity usually 



ashy, with a broad or narrow dark brown or blackish 



1)and below the middle and a narrow dark band at the top, 



the constituent leaves with a narrow central groove, 4-cari- 



nate; teeth dark brown, mostly cohering in groups by 



their pale membranous borders, tardily deciduous ; spikes 



exserted or not, 1-3 cm. long, sharply apiculate. 



Moist alluvial situations, often in shade; Alaska to California 

 (Santa Clara County), Nevada, Arizona, and New Me.xico. Type 

 locality: California. 



