Flora of the Palouse Region 



Order 5. EQUISETEAE. 



Branches when present whorled: sporangia one-celled, clustered 

 under the scales of the terminal cone-like spikes; spikes of but one 

 kind: spores furnished with narrow ribbon-like appendages (elaters) 

 attached at the middle, coiling around them when moist and 

 spreading in the form of a cross when dry and mature: epidermis 

 impregnated with silica, rough. 



Family 5. EQUISETACEAE. 



Characters of the Order. 



10. EQUISETUM. 



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 appearing in spring 



before the herbaceous sterile ones. E. arvense. 



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

 Ridges of the stem somewhat roughened with tubercles. 



E. ROBUSTUM. 

 Ridges of the stem nearly smooth. E. laeyigaTum. 



E. 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 numerous 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. 



E robustum A. Braun. 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. The species is variable and probably 

 not distinct from E. hiemale L. 



E. 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 ex- 

 ceeds the uppermost sheath. 



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

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

 produced, resulting in a form very similar to B. variegatum Schleich. 



