HORSETAIL FAMILY 



39 



Stems deeply 5-10-angled, slender, with a very small central cavity; sheaths dilated, loose. 



3. E. palustre. 

 Stems shallowly 10-30grooved, stout, with a very broad central cavity; sheaths cylindrical, 

 appressed. 4. E. fluiiatile. 



Fertile stems mostly unbranched above ground, sometimes (toward maturity) developing small ver- 

 ticillate branches; plants of dry or ordinarily moist situations. 



Stems very rough, the ridges with sharply projecting cross-bands of silica; limb of sheaths strongly 

 incurved with age; a diffuse tuft of many-branched sterile stems usually borne at the base of the 

 erect fertile ones. 5. E. fuiistoni. 



Stems smooth or nearly so, the ridges with or without cross-bands of silica; limb of sheath incurved 

 or not; diffuse basal tuft of branched sterile shoots wanting. 6. E. kansanum. 



Spikes rigidly apiculate; aerial stems evergreen, persisting 2 or more years. 



Stems 5-12-angled; central cavity half the diameter of the stem, or less, or wanting; leaves and teeth not 

 sharply differentiated. 

 Central cavity one-third to half the diameter of the stem; sheaths 5-12-toothed. 7. E. variegatum. 



Central cavity wanting; sheaths 3-toothed. 8. E. scirpoides. 



Stems 16-48-angled; central cavity more than half the diameter of the stem; leaves and teeth sharply 

 differentiated. 



Sheaths much longer than broad, dilated above, somewhat funnel-shaped, mostly green, the lower 

 ones w-ith a dark band. 9. E. laevigatum. 



Sheaths nearly or quite as broad as long, nearly cylindrical, tight, mostly ashy at maturity, with 

 2 dark bands. 



Ridges of the stem with a row of elevated cross-bands of silica; leaves sharply 3-carinate, the cen- 

 tral keel rarely grooved. 10. E. praealtitm. 



Ridges of the stem usually with 2 distinct rows of silica tubercles; leaves 4-carinate, the central 

 groove narrow but usually well defined. 11. £. hiemale calif ornicum. 



\. Equisetum arvense L. 

 Common Horsetail. Fig. 81. 



Equisetum arrense L. Sp. PI. 1061. 1753. 



Rhizome slightly angled, felted, tuber-bearing 

 Fertile stems erect, 5-25 cm. long, flesh-colored, 

 smooth, succulent, soon withering; internodes 2-8; 

 sheaths pale, loose, with 8-12 large, brownish, lanceo- 

 late teeth ; spike lance-ovoid, 2-3 cm. long, peduncu- 

 late. Sterile stems prostrate to erect, 10-60 cm. 

 long, green, 6-14-furrowed, roughish, the silex in 

 roundish dots ; branches numerous, in dense verticils, 

 usually simple, solid, prominently 3- or 4-angled, their 

 sheaths with triangular-lanceolate, erect, sharp-pointed 

 teeth. 



Thickets, open sandy banks, and alluvial situations, rarely in 

 deep shade; Alaska to Labrador and Newfoundland, southward 

 nearly throughout the United States; Greenland; Eurasia. 

 Type locality, European. E.xtremely variable in habit and size, 

 but offering no permanent varieties. 



2. Equisetum telmateia I'Lhrh. 

 Giant Horsetail. Fig. 82. 



Equisetum telmateia Ehrh. Hannov. Mag. 1783: 287. 1783. 



Rhizome, slightly grooved, felted, tuber-bearing. 

 Fertile stems erect, often clustered, 25-60 cm. long, 

 1-2.5 cm. thick, white or brownish, smooth, suc- 

 culent, soon withering ; sheaths loose, brownish, 

 membranous, 2-5 cm. long, the lower ones longer 

 than the internodes ; teeth 20-30, attenuate, coher- 

 ing in groups of 2 or 3 ; spikes stout-pedunculate, 

 4-8 cm. long, 1-2.5 cm. thick. Sterile stems erect, 

 0.5-3 meters long, 5-20 mm. thick, white or pale 

 green ; internodes 2-9 cm. long, 20-40-furrowed, the 

 ridges smooth; sheaths cylindrical, appressed, with 

 20^0 teeth, these elongate, with broad hyaline 

 margins, usually coherent in groups ; branches in 

 dense spreading verticils, solid, simple, 4-6-angled, 

 the keel very rough with cross-bands of silica. 



Swamps and borders of streams. Transition Zone; British 

 Columbia to southern California; Eurasia; north Africa. 

 Type locality, European. Intermediate, partially fertile 

 forms are found occasionally. 



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