FLOWERING PLANTS AND FERNS OF ARIZONA 43 



branches at the solid sheathed nodes; leaves minute, united lengthwise 

 to form nodal sheaths, the tips free or connivent, persistent or de- 

 ciduous; fruit a terminal cone formed of stalked peltate bracts, these 

 bearing a few sporangia beneath; spores uniform, provided with 

 4 hygroscopic bands; gametophytes minute, dioecious, green. 



1. EQUISETTM. Horsetail 

 Key to the species 



1. Aerial stems dimorphous, the fertile ones flesh-colored, succulent, withering; 

 sterile stems green, with numerous slender branches in dense verticils. 



1. E. arvex.se. 

 1. Aerial stems uniform, simple or sometimes a few branches borne basally or in 

 irregular whorls (2). 



2. Spikes blunt or acutish; aerial stems annual 2. E. kansanum. 



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

 sons (3). 

 3. Sheaths distinctly longer than broad, dilated upward, the lower ones with 



a dark band below 3. E. laevigatum. 



3. Sheaths nearly or quite as broad as long, nearly cylindric, tight, mostly 

 ashy at maturity, with 2 dark bands (4). 

 4. Ridges of the stem with a row of elevated cross bands of silica; leaves 

 sharply 3-carinate, the central keel sometimes grooved. 



4. E. PREALTUM. 



4. Ridges usually with 2 distinct rows of silica tubercles; leaves 4-carinate, 

 the central groove usually well defined 5. E. hyemale. 



1. Equisetum arvense L., Sp. PL 1061. 1753. 



Near Flagstaff (Coconino County), Ryan Ranch, White Mountains 

 (Apache County), Sierra Ancha (Gila County), 6,000 to 7,000 feet, 

 moist soil along streams. Newfoundland and Labrador to Alaska, 

 southward nearly throughout the United States; Greenland; Eurasia. 



2. Equisetum kansanum Schaffn., Ohio Nat, 13: 21. 1912. 

 Coconino, Yavapai, Gila, Cochise, and Pima Counties, 5,000 to 



8,000 feet, marshes and springy places; sometimes a weed in cultivated 

 land. Ontario to British Columbia, southward to Ohio, Texas, New 

 Mexico, Arizona, and southern California; northern Mexico (Chi- 

 huahua) . 



3. Equisetum laevigatum A. Br., Amer. Jour. Sci. 46: 87. 1844. 



Equisetum hyemale var. intermedium A. A. Eaton, Fern Bui. 10: 



120. 1902. 

 Equisetum intermedium Rydb., Fl. Rocky Mount. 1053. 1917. 



Tuba and near Flagstaff (Coconino County), near Fort Huachuca 

 (Cochise County), 5,000 to 7,000 feet; moist alluvial thickets and 

 sandy banks. New York to British Columbia, south to Illinois, 

 Missouri, Texas, and the Mexican border region to southern Cali- 

 fornia; Mexico and Guatemala. 



4. Equisetum prealtum Raf., Fl. Ludovic. 13. 1817. 



Equisetum robustum A. Br., Amer. Jour. Sci. 46: 88. 1844. 



Chinle Creek (Apache County), Oak Creek Canyon (Coconino 

 County), Sierra Ancha (Gila County), Chiricahua and Euachuca 

 Mountains (Cochise County), Santa Catalina Mountains (Pima 

 County), 5,000 to 7,000 feet, springy places and along streams. Nova 

 Scotia to British Columbia, southward nearly throughout the United 

 States; Mexico. 



