EQUISETACEAE (HORSETAIL FAMILY) 23 



3. MARSILEACEAE R. Br. 



Perennial herbaceous plants rooting in the mud, with slender creeping root- 

 stocks, and 4-foliate or filiform long-petioled leaves. The sporocarps borne at 

 the base, either sessile or on a stipe (petiole), crustaceous, ovoid or bean- 

 shaped, 2-valved, several-celled and containing both megaspores and micro- 

 spores; the former give rise to prothallia producing archegonia; the latter to 

 prothallia producing antheridia. 



MARSILEA L. 



Characters of the family: 



Sporocarp toothed above 1. M. vestita. 



Sporocarp rounded above . . . . . . . . . 2. M. oligospora. 



1. Marsilea vestita Hook. & Grev. Ic. Fil. PL 159. 1831. Slender, 8-15 

 cm. high: leaflets broadly cuneate, entire or slightly toothed: sporpcarp 4-7 

 mm. long, 3-5 mm. wide, densely covered with soft spreading hair-like scales; 

 the lower tooth short and blunt; the upper acute, longer, sometimes curved: 

 sori in each valve 1011; megaspores in each sorus 12-20 (usually 15-18). 

 Variable and widely dispersed but rare; possibly not within our range. 



2. Marsilea oligospora L. N. Good. Bot. Gaz. 33: 66. 1902. Plant 4-7 cm. 

 high: leaflets woolly or becoming glabrous, 6-10 mm. long, 3-7 mm. wide: 

 sporocarp solitary, 4-6 mm. long, 4-5 mm. wide, covered with long, straight 

 and appressed (rarely somewhat woolly) pubescence : raphe short : lower tooth 

 short and blunt, upper a mere rounded papilla or wanting: peduncle 5-8 mm. 

 long: sori 5-8 in each valve; megaspores oval to barely oblong, 6-9 in each 

 sorus. Northwestern Wyoming (Jackson's Hole and Yellowstone Park). 

 Possibly the Rocky Mountain specimens all belong to this rather than to the 

 preceding species. 



4. EQUISETACEAE Michx. HORSETAIL FAMILY 



Perennials with subterranean rootstocks. Stems rush-like, simple or 

 branched, striate, jointed, usually hollow. Leaves of two kinds: the sterile 

 reduced to toothed sheaths at the nodes; the fertile shield-shaped and form- 

 ing a short spike terminating the stem. Occurring mostly in moist or sandy 

 situations. 



1. EQUISETUM L. HORSETAIL. SCOURING RUSH 



Stems simple or branched, the joints having closed ends. Leaves of the 

 fruiting cones 5-7-angled, with sporangia hood-like. Spores round, furnished 

 with two slender filaments attached by the middle and clavate at the free 

 ends. Prothallia above ground, green, usually dioecious. 



Stems dying down to the ground each year. 



Stems of two kinds; the fertile simple; the sterile with whorls of slen- 

 der branches at the nodes. 

 Fertile stems withering early . . . . . . . 1. E. arvense. 



Fertile stems persisting for the season. 2. E. pratense. 



Stems all alike, simple. 



Sheaths with about 8 white-margined teeth . . . . . 3. E. palustre. 



Sheaths with about 18 dark-brown teeth 4. E. fluviatile. 



Stems perennial, evergreen. 

 Stems many-grooved. 



Rough with conspicuous tubercles. 



Stems thick, often 1-3 m. high 5. E. robustum. 



Stems slenderer, mostly less than 5 dm. high . . , . 6. E. hiemale. 



Nearly smooth, the tubercles inconspicuous 7. E. laeyigatum. 



Stems with only 6-10 grooves . , 8. E. variegatum. 



