24 ISOETACEAE (qUILLWORT FAMILY) 



1. Ec[uisetum arvense L. Sp. PI. 1061. 1753/ Stems of two kinds; the 

 fertile in early spring, soft, pale or brownish, with loose and usually distant 

 8-12-toothed sheaths, 1-2 dm. high, crowned by the short spike of sporophylls, 

 withering early; the sterile stems slender, becoming 3-5 dm. high, 10-14- 

 furrowed, with numerous verticillate 4-angled soUd slender branches with 

 4-toothed sheaths. Common Horsetail. — Across the continent; also in 

 Europe and Asia. 



2. Equisetum pratense Ehrh. Hanov. Mag. 138. 1784. Differing from 

 the preceding in that the fertile stem is persistent, withering (after the spores 

 are shed) only at summit, then putting out branches and becoming like the 

 sterile in appearance: branchlets triangular with 3-toothed sheaths. — Re- 

 ported from Colorado, but rare in our range. 



3. Equisetum palustre L. Sp. PI. 1061. 1753. Stems all alike, slender, 

 2-4 dm, high, deeply 5-9-grooved, with conspicuous wing-like ridges: sheaths 

 with about 8 lance-subulate teeth: branches few, short; their sheaths about 

 5-toothed. — Scarcely within our range, but possibly occurring from Wyoming 

 to Montana and thence across the continent, and northward, 



4. Equisetum fluviatile L. Sp. PI. 1062. 1753. Stems 5-8 dm. high, at 

 first simple and then t^ed with the short spike of sporophylls, later produc- 

 ing erect yellow branches; furrows numerous, inconspicuous: sheaths ap- 

 pressed with about 18 dark brown, short, acute, rigid teeth. — In bogs and in 

 the borders of shallow ponds, northwestern Wyoming and Montana and thence 

 across the continent northward. 



5. Equisetum robustum A. Br., Engelm. Am. Journ. Sci. 46: S8. 1844. 

 Stems evergreen, usually very stout and tall, often 1 m. or more high and 

 2 cm. in diameter: the ridges narrow, rough with one line of tubercles: sheaths 

 short, with a black girdle above the base, rarely with a black limb, teeth abqut 

 40, 3-keeled, ovate-subulate, deciduous. — In many parts of North America 

 north of Mexico; also in Asia. 



6. Equisetum hiemale L. 1. c. Stems lower and slenderer, 3-8 dm. high: 

 the ridges roughened by two more or less distinct Hnes of tubercles: sheaths 

 elongated, with a black girdle above the base and a black limb of about 20 

 (17-26) narrowly linear teeth, 1-keeled at the base and with subulate de- 

 ciduous points: spikes tipped with a rigid point. The common Scoueing 

 Rush. — Nearly throughout North America; also in Europe and Asia. 



7. Equisetum laevigatum A. Br., Engelm. Am. Journ. Sci. 46: 87. 1844. 

 Stems 3-10 dm. high, sometimes with numerous branches: the ridges convex, 

 obtuse, smooth or barely roughish with minute tubercles: sheaths elongated, 

 with a narrow black limb and about 22 linear-subulate caducous teeth, 

 1-keeled below. — From New Mexico to Canada and across the continent. 



8. Equisetum variegatum Schleich. Cat. PL Helvet. 27. 1807. Stems in 

 tufts from a branched base, slender, ascending, 2-5 dm. high, usually simple, 

 only 5-10 grooved: sheaths green, variegated with black above; the 5-10 teeth 

 tipped with a deciduous bristle. — Colorado to Utah and Wyoming and almost 

 across the continent. 



5. ISOETACEAE Underw. Quillwort Family 



Mostly aquatic plants, with a short solid corm-like stem (trunk) and elon- 

 gated grass-like leaves, the bases of which are expanded and have thin stipule- 

 like infolded margins (the velum), which inclose large simple ovoid thin- walled 

 sporangia; the outer ones containing large spherical megaspores; those of the 

 inner leaves filled with very minute grayish microspores. 



1. ISOETES L. QuiLLWOET 



Characters those of the family. For an elaboration of the genus, see Under- 

 •wood's Our Native Ferns. Our species (as reported at present) belong to the 



