Genus i. 



HORSETAIL FAMILY. 



39 



i. EQUISETUM [Tourn.] L. Sp. PI. 1061. 1753. 



Characters of the family. [Name ancient, signifying horse-tail, in allusion to the copious 

 branching of several species.] Called also Toad-pipe, Tad-pipe. 



About 25 species, of very wide geographic distribution. Type species : Equiselum fiuviatile L. 



Stems annual ; stomata scattered. 



Stems of two kinds, the fertile appearing in early spring before the sterile. 



Fertile stems simple, soon withering ; sheaths of branches of sterile stems 4-toothed. 



1. E. arvense. 

 Fertile stems branched when old, only the apex withering. 



Branches of the stem simple, their sheaths 3-toothed. 2. E. pratense. 



Branches compound. 3. E. sylvaticum. 



Stems all alike ; spores mature in summer ; branches simple or none. 



Sheaths rather loose ; branches usually long ; stems bushy below, attenuate upwards. 

 Central cavity very small ; spike long. 4. E. palustre. 



Central cavity about one-half the diameter of stem ; spike short. 5. E. littorale. 



Sheaths appressed ; branches usually short. 6. E. fiuviatile. 



Stems mostly perennial, evergreen ; spikes tipped with a rigid point ; stomata in regular rows. 

 Stems tall, usually many-grooved. 



Stems rough and tuberculate, prominently ridged. 



Ridges with 1 line of tubercles ; ridges of sheath tricarinate ; stem stout. 



7. E. robustum. 

 Ridges of the stem with 2 indistinct lines of tubercles ; ridges of sheath obscurely 4- 

 carinate ; stem slender. 8. E. hyemale. 



Stems not tuberculate ; sheaths enlarged upward. 9. E. laevigatum. 



Stems low, slender, tufted, usually 5-10-grooved. 



Central cavity small; sheaths 5-10-toothed. 10. E. variegatum. 



Central cavity none; sheaths 3-toothed. 11. E. scirpoides. 



1. Equisetum arvense L. 

 Fig. 89. 



Field Horsetail. 



Equisetum arvense L. Sp. PI. 1061. 1753. 



Stems annual, provided with scattered stomata, the 

 fertile appearing in early spring before the sterile. 

 Fertile stems 4'-io' high, not branched, soon wither- 

 ing, light brown, their loose scarious sheaths mostly 

 distant, whitish, ending in about 12 brown acuminate 

 teeth; sterile stems green, rather slender, 2'-2° high, 

 6-iQrfurrowed, with numerous long mostly simple verti- 

 cillate 4-angled or rarely 3-angled solid branches, the 

 sheaths of the branches 4-toothed, the stomata in 2 rows 

 in the furrows. 



In sandy soil, especially along roadsides and railways, 

 Newfoundland and Greenland to Alaska, _ south to Virginia 

 and California. Also in Europe and Asia. Ascends to at 

 least 2500 ft. in Virginia. An occasional form in which 

 the sterile stem bears a terminal spike is known as var. 

 serotinum. Sterile stems sometimes very short and with 

 long prostrate or ascending branches. Called also Corn- 

 field Horsetail ; Bottlebrush, Horse- or Snake-pipes ; Cat's- 

 tail. May. 



2. Equisetum pratense Ehrh. Thicket or Meadow 

 Horsetail. Fig. 90. 



Equisetum pratense Ehrh. Hanov. Mag. 9: 138. 1784. 



Stems annual, 8'-i6' high, with scattered stomata, the 

 fertile appearing in spring before the sterile, branched 

 when old, only its apex withering, the two becoming similar 

 in age ; stems rough, 8-20-ridged with narrow furrows and 

 cylindric or cup-shaped sheaths; branches straight, rather 

 short, simple, densely whorled, 3-angled or rarely 4-5- 

 angled, solid; sheaths of the stem with about 11 short 

 ovate-lanceolate teeth, those of the branches 3-toothed; 

 rootstocks solid, acutely angled. 



In sandy places, Nova Scotia and Rupert River to Minne- 

 sota, and Alaska, south to New Jersey, Iowa and Colorado. 

 Also in Europe and Asia. July-Sept. 



