1052 EQUISETACEAE 



Sheath close; central cavity one-half of the diameter of the stem or more 

 Sheaths 7-8 mm. long; stem stout, spariiif^ly branched. 5. E. fluviatile. 

 Sheaths less than 5 mm. long; stem slender, much branched. (Autumnal 

 ^ , , fonns of) 1. E. arvense. 



Teeth of the sheatlis deciduous ; plant unbranched or nearly so. 

 c,^ . , 6. E. kansanum. 



Stem pereimial, evergreen (except sometimes in E. laevigatum), mostly simple; spike 

 apiculate, with a rigid tip; stomata in regular rows. 

 Central cavity present; stem more than 6-angled, except sometimes in E. variegatum. 

 Teeth of the sheaths deciduous; stem tall and stout, many-grooved. 

 Stem tubercled, rough. 



Sheath close, usually with a black or dark ring near the base, then grayish 

 and with a narrow dark border at the base of the teeth. 

 Stem 1-2 m. high, stout; sheaths as broad as long. 7. E. robuslum. 

 Stem 0.3-1 m. high, slender; sheath longer than broad. 



8. E. affine. 

 Sheaths more ampUate above, green, with or without a narrow border, 

 but no ring below. g. E. intermedium. 



Stem not tubercled, smooth; sheaths enlarged upwards, with or without a dark 

 margin, but rarely with a rmg below. 10. E. laevigatum. 



Teeth of the sheaths persistent, white-margined; stem low, slender, 5-10-grooved. 

 ^ , 11. E. variegatum. 



Central cavity wantmg; stem 6-angled. 12. E. scirpoides. 



1. E. arvense L. Spore-bearing stems 1-2.5 dm. high, 3-5 mm. in diameter, 

 with loose 8-12-toothed sheaths, rarely with a few branches; cones pedimcled, 

 2-4 cm. long, ,5-10 mm. thick; sterile stems decumbent to erect, 1-3.5 dm. high, 

 2-3 mm. thick, 10-14-furrowed, branched; branches 3-4-angled, solid; teeth of 

 the sheaths lanceolate, acuminate. In the fall the sterile stems sometimes bear 

 small cones 4-10 mm. long, mostly with sterile spores (var. serotinum). Wet 

 banks: Greenl. — S.C. — Calif. — Alaska; Eurasia. Plain — Alp. 



2. E. sylvaticum L. Stems 1-4.5 dm. high, 8-14-riaged, 3-4 mm. thick; 

 both the fertile and the sterile ones branched; central cavity constituting half 

 the diameter; sheaths brown, loose, the teeth more or less coherent; primary 

 branches 4-5-angled, the secondary ones 3-angled; cones peduncled, 1-3 cm. 

 long, 5-8 mm. thick. Wet shady places: Newf. — Va. — la. — B.C. — Alaska; 

 Eurasia. Suhmont. — Mont. My-Je. 



3. E. pratense Ehrh. Stems 2-4 dm. high, 3-5 mm. thick, 8-20-ridged. 

 the fertile ones at first nearly unbranched, some developing short spreading 

 branches, the sterile ones with long branches; central cavity one-third the diam- 

 eter; sheaths green, loose; teeth lanceolate with dark middle; branches 3-ridged; 

 teeth of the sheaths deltoid; cones pedimcled, 1-2 cm. long, about 5 mm. thick. 

 Alluvial soil: N.S. — N.J. — Colo. — Alaska; Eurasia. Suhinont. — Subalp. Ap- 

 My. 



4. E. palustre L. Stems 2-9 dm. high, 3-5 mm. thick, 5-10-angled ; branches 

 long, ascending, hollow, 4r-7-angled; sheaths widened upwards; teeth lance-subu- 

 late; cones 1.5-2.5 cm. long, 5-6 mm. thick. Wet places: Newf. — Conn.— Wyo. 

 — Wash. — Alaska; Eurasia. Suhmont. — Mont. Je-Au. 



5. E. fluviatile L. Stems 3-15 dm. high, 4-8 mm. thick, 10-30-angled; 

 central cavity four-fifths of the diameter; branches spreading or upcurvod, long, 

 4-6-angled, hollow; sheaths appressed; teeth dark brown, distinct, narrow; cones 

 short-pedimcled, 1.5-2.5 cm. long, 5-7 mm. thick. E. limosum L. Shallow 

 water: Newf.— N.Y.— Wyo.— Wash.— B.C. Plain— Mont. Je-Jl. 



6. E. kansanum J. H. Schaffner. Stems 3-5 dm. high, 15-30-grooved, 

 light green; sheaths long, dilated above, green, with a narrow black band at the 

 top, rarely with a faint one below; cones short-peduncled, ovate or ovate-oblong, 

 1.5-2.5 cm. long, 7-8 mm. thick. Clay banks: Mo. — Utah — Mont. Plain — 

 Subtnont. 



7. E. robustum A. Br. Stems 1-3 m. high, 8-12 mm. thick, 16-48-angled, 

 dark green; ridges rounde<l, rough, with 3 rows of tubercles; sheath tight, about 

 as broad as long; teeth mostly ])ersistent, lance-linear, sharply 3-anglcd, black, 

 with white margins; spike sessile, 1.5-2.5 cm. long, 6-7 mm. thick, strongly 

 apiculate. N.Y.—Md.— La.— Tex.— Calif.— B.C. Plain— Suhmont. Je-Au. 



8. E. affine Engelm. Stems 3-10 dm. nigh, 4-8 mm. thick, 16-40-angIed, 

 dark green; ridges rounded, rough with 2 rows of tubercles; sheaths longer than 



