20 EQUISETACEAE 



FAMILY 2. SALVINIACEAE Keichenb. SALVINIA FAMILY. 

 Small floating plants, with a more or less elongated and sometimes branch- 

 ing axis bearing apparently 2-ranked leaves. Sporocarps soft, thin-walled, 

 borne 2 or more on a common stalk, 1-celled, with a central often branched re- 

 ceptacle, which bears macrosporanges containing a single macrospore or micro- 

 sporanges containing numerous microspores. 



1. AZOLLA Lain. 



Minute moss-like reddish or green floating plants, with pinnately branched stems cov- 

 ered with minute imbricated 2-lobed leaves, and emitting rootlets beneath. Sporocarps of 

 two kinds borne in the axils of the leaves, the smaller ovoid or acorn-shaped, containing 

 a single macrospore at the base and a few minute bodies above it, the larger globose, pro- 

 ducing many pedicelled sporanges, each containing several masses of microspores. 



1. Azolla Caroliniana Willd. Plants greenish or reddish, 2-4 mm. broad, deltoid 

 or triangular-ovate, pinnately branching, sometimes covering large surfaces of water. 

 Macrospores minutely granulate, with three accessory bodies ; masses of microspores 

 armed with rigid septate processes : leaves with ovate lobes, their color varying with the 

 amount of sunlight, the lower usually reddish, the upper green with a reddish border. 



Floating on still water, Ontario to British Columbia, south to Florida, Arizona and Mexico. 



Order 4. EQUISETALES. 



Rush-like perennial plants, with horizontal rootstocks and mostly hollow 

 jointed simple or often much-branched grooved stems, provided with a double 

 series of cavities and usually with a large central one, the branches whorled, the 

 nodes provided with diaphragms. Leaves reduced to toothed sheaths at the 

 joints. Sporanges 1-celled, clustered underneath the scales of terminal cone- 

 like spikes. Spores uniform, furnished with 2 narrow appendages (elaters) at- 

 tached at the middle, coiling around the spores when moist, and spreading, when 

 dry, in diverse ways. Prothallia terrestrial, green, usually dioecious. 



FAMILY 1. EQUISETACEAE Michx. HORSETAIL FAMILY. 

 Characters of the order. 

 Theonly genus. * EQUISETTJM L. 



Stems annual, of 2 kinds; fertile vernal, simple, soon withering; sterile much branched: stomata 



scattered. 1. E. arvense. 



Stems perennial : spikes rigid-pointed : stomata in regular rows. 

 Stems rough and tuberculate, prominently ridged. 



Stems stout : ridges with 1 line of tubercles : sheaths with 3-keeled lidges. 2. E. robustum. 



Stems slender : ridges with 2 indistinct lines of tubercles : sheaths with obscurely 



4-keeled ridges. 3. E. hyeniale. 



Stems not tuberculate : sheaths enlarged upward. 4. E. laevigatum. 



1. Equisetum arvense L. Stems annual, with scattered stomata, the fertile appear- 

 ing in early spring before the sterile. Fertile stems 1-2.5 dm. high, not branched, soon 

 withering, light brown, their loose scarious sheaths mostly distant, whitish, ending in about 

 12 brown acuminate teeth ; sterile stems green, rather slender, 0.5-6 dm. high, 6-19-fur- 

 rowed, with numerous long mostly simple whorled 4-angled or rarely 3-angled solid 

 branches, their sheaths 4-toothed, the stomata in two rows in the furrows. 



In sandy soil. Newfoundland, Greenland and Alaska, south to North Carolina and California. Also 

 in Europe and Asia. E. arvense serotinum is an occasional form with a cone terminating the normally 

 sterile plant. Spring. HORSETAIL. 



2. Equisetum robtistum A. Br. Stems perennial, stout, tall, evergreen, 1-2.5 m. 

 high, sometimes 2 cm. in diameteV, 20-48-furrowed, simple or little branched. Kidges 

 roughened with a single series of transversely oblong siliceous tubercles : sheaths short, 

 cylindric, appressed, marked with black girdles at the base, and at the bases of the dark 

 caducous teeth ; ridges of the sheath 3-carinate ; branches, when present, occasionally 

 fertile : spikes tipped with a rigid point. 



In wet places, Ohio to British Columbia, south to Louisiana, California and Mexico. Also in Asia. 



3. Equisetum hyemale L. Stems slender, rather stiff, evergreen, 6-12 dm. high, 

 with the stomata arranged in rows, rough, 8-34-furrowed, the ridges with two indistinct 



