5. Ophioglossaceae 41 



4. Equisetaceae Rich. — Horsetail Family 

 1. Equisetum L. 



1. Stems all alike, usually simple; stomata in regular rows in the 

 grooves. 

 2. Stems usually tall, 10- to 50-angled, hollow; teeth of the sheaths 

 soon deciduous. 

 3. Sheaths about as long as broad, short-cylindrical, appresscd, 

 ashy-gray, with a black band near the base; stems dark 

 green, perennial, rough-tuberculate; cones rigidly apicu- 

 late; moist sandy soil, common. Tall Scouring-rush [E. 

 prealtum Raf.]* E. hyemale L. 



3. Sheaths slightly longer than broad, dilated upward and some- 



what fimnelform, green, and usually with a narrow black 

 rim; stems pale, annual, smooth or nearly so; cones blunt 

 or with a small apiculus; sandy soil, common. Smooth 

 Scouring-rush [E. kansanum Schaffner] ....E. laevigatmn A.Br. 

 2. Stems low, slender, 5- to 10-angled; teeth of the sheaths persist- 

 ent; cones apiculate. 



4. Stems 15-30 cm tall, 1-3 mm thick, 5- to 10-angled; central 



cavity one-third the diameter of the stem; sheaths 5- to 10- 

 toothed ; cones 5-10 mm long; moist sandy soil in the n. 

 half of the state. Variegated Scouring-rush [E. nelsoni 



(A.A.Eaton) SchafTner] E. variegaturn Schleich. 



4. Stems 5-15 cm tall, 0.5-1 mm thick, 6-angled; central cavity 

 absent; sheaths mostly 3-toothed; cones 3-5 mm long; 

 moist ground, rare. Lake and McHenry counties. Dwarf 



Scouring-rush E. scirpoides Michx. 



1. Stems annual, flexible; stomata scattered: cones blunt. 

 5. Stems all alike, green, usually branched at inaturity. 



6. Stems 10- to 30-grooved; central cavity one-half or more the 

 diameter of the stem; sheaths tight; along ditches or in 

 marshes or shallow water in the n. half of the state. Water 



Horsetail E. fluviatile L. 



6. Stems 5- to 10-angled; central cavity about one-sixth the 

 diameter of the stem; sheaths loose; wet soil, rare. Peoria 



and Tazewell counties. Marsh Horsetail E. palustre L. 



5. Stems of two kinds, the sterile green and branched, the fertile 

 whitish or brownish, appearing in early spring and soon 

 withering; moist sandy soil, common, particularly on railroad 

 embankments. Field Horsetail E. arvense L. 



5. Ophioglossaceae Presl — Adder's-tongue Family 

 1. Sterile blade pinnately divided; venation free; sporangia in a panicle 



1. Botrychium 



1. Sterile blade simple, entire; venation reticulate; sporangia in two rows in 



a simple slender spike 2. Ophioglossum 



* 



Synonyms appear in brackets. 



