6 SELAGINELLACEAE. 



11. EQUISETUM. HORSETAIL. 



Perennial plants with extensively creeping rootstocks; stems 

 simple or with whorled branches, furrowed lengthwise, hollow; 

 sporangia adhering on the under side of the shield-shaped scales 

 of the spike, one-celled, opening down the inner side; spores of 

 one kind, with elaters. 



Stems annual, of two kinds, the pale brown fertile ones appear- 

 ing in spring before the herbaceous sterile ones; spikes not 

 apiculate. E. arvense. 



Stems perennial, all alike, evergreen; spikes tipped with a rigid 



point. 



Ridges of the stem somewhat roughened with tubercles. E. hyemale. 

 Ridges of the stem nearly smooth. E. laevigatum. 



Equisetum arvense L. Aerial stems annual, of two kinds; the fertile 

 pale-brown and short-lived, appearing in early spring before the sterile; 

 fertile stems 10-20 cm. tall, simple, terete, bearing about four loose scarious 

 distant sheaths, these whitish with about 12 brownish acuminate teeth; 

 sterile stems pale green, 10-40 cm. tall, marked with 6-19 furrows, with numer- 

 ous whorls of mostly simple, solid branches, these 4-angled or rarely 3-angled ; 

 cavity of the main stem small; spike 2-3 cm. long. Common in moist places. 



Equisetum hyemale robustum (A. Br.) A. A. Eaton. Scouring rush. 

 Aerial stems evergreen, all alike, 40-120 cm. tall, 5-20 mm. thick, marked with 

 20^36 furrows; ridges roughened usually with a single series of transverse 

 siliceous tubercles; sheath short, commonly marked with a black girdle at the 

 base and another at the base of the early-falling teeth; spike nearly sessile in 

 the uppermost sheath, 2-3 cm. long, tipped with a rigid point. 



Common in moist places. The stems are usually simple but under certain 

 conditions branches may be produced. 



Equisetum laevigatum A. Braun. Aerial stems evergreen, pale, mostly 

 simple, 40-90 cm. tall, marked with 14-30 furrows, the ridges nearly smooth; 

 each sheath marked with a black girdle at the base of the deciduous white- 

 margined teeth, and sometimes with another at its base; wall of the stem thin, 

 the cavity large; spikes 2-3 cm. long, borne on a stalk that usually exceeds 

 the uppermost sheath. 



Common in low ground, on railway embankments, etc. When the primary 

 stems are cut off near the base a large number of smaller stems are produced, 

 resulting in a form very similar to E. variegatum Schleich. 



Class III. LYCOPODINEAE. 



Plant moss-like; stems branched, solid, with numerous 

 small leaves; sporangia solitary in the axils of the leaves or 

 on their upper surface. 



Family 5. SELAGINELLACEAE. 



Terrestrial, annual or perennial moss-like plants with branching 

 stems and scale-like leaves, which are many-ranked and uniform, 

 or four-ranked and of two kinds spreading in two planes; spo- 



