velum variable, from very narrow to covering nearly one half of sporangium; 

 megaspores 280-440 microns in diameter, marked with low tubercles, frequently 

 confluent into short low wrinkles; microspores frequently ashy-gray, 20-30 microns 

 long, finely spinulose. Incl. var. pallida Engelm. 



In shallow ponds, bogs, old buffalo wallows, wet thickets and woods (especially 

 pinelands), in seasonal streams and temporary sedge-grass puddles in meadows 

 and prairies, and in temporary pools on granite outcrops, rare in Okla. (Atoka 

 Co.), widely distributed but uncommon in e. Tex., w. to Mason Co. on Edwards 

 Plateau, Mar.-Oct.; from N.J., w. to Minn., 111. and S.D., s. to Ga., La., Okla. and 

 Tex. 



4. Isoetes Butleri Engelm. 



Superficially resembling a pale-based form of /. melanopoda, smaller, dioecious; 

 leaves 8 to 30, almost bristleform, with triangular cross section, 8-22 cm. long, 

 0.5-1.2 mm. broad, pale at base, with broad dissepiments, slender air-canals and 

 4 bast-bundles, the pale sheaths granular on the back; sporangia 6-7 mm. long, 

 commonly covered with brown lines, with velum wanting or very narrow; ligule 

 subulate, with the base cordate; megaspores (360-) 480-650 microns in diameter, 

 covered with many low and distinct (sometimes confluent) wartlike tubercles; 

 microspores 27-37 microns long, covered with papillae. 



Rocky slopes, springy places, seepage areas, flats and depressions in Okla. 

 (Atoka Co.); Tenn., Mo. and e. Kan., s. to Ark. and Okla. 



Fam. 5. Equisetaceae Rich. Horsetail or Scouring-rush 

 Family 



Large or small terrestrial rushlike plants with wide-creeping branching perennial 

 rhizomes; roots felted, annual; aerial stems usually erect, perennial or annual, 

 cylindric, fluted, stout or slender, jointed, simple or with whorls of branches 

 at the solid nodes, with usually hollow internodes, often roughened by a coating 

 of silex; stomata arranged in regular rows or broad bands in the grooves; stem 

 leaves minute, reduced and united to form toothed sheaths at the nodes, the 

 free or connivent apical teeth persistent or deciduous; sporophylls aggregated 

 into a cone or strobile at the summit of the main stem or at the apex of the 

 branches, modified as stalked peltate scales; sporangia 6 or 7 under each scale, 

 opening down the inner side; spores all alike, numerous, green; prothallia in 

 damp places above ground, green, monoecious or dioecious, variously lobed. 



The family is represented only by the following genus. 



Our species are of lesser importance to animal and bird life than those found 

 farther north. The plants are incidentally browsed and eaten by cattle, deer and 

 muskrats, and some waterfowl are known to eat the rootstocks and stems. 



1. Equisetum L. 



Characters same as those of the family. A complex genus consisting of about 

 23 species that are widespread in both hemispheres. 



1. Aerial stems dimorphic; fertile stems light-brown, early-withering; sterile stems 

 green, with regular whorls of branches 1. E. arvense. 



1. Aerial stems uniform, without regular whorls of branches (2) 



2(1). Cones rounded at the summit, without a firm sharp tip; stems annual, soft 

 and easily crushed 2. E. kansanum. 



2. Cones tipped by a firm dark point; stems perennial (evergreen), firm and 



resistant or somewhat soft (3) 



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