1B. Stomates in single vertical lines on either side of valleys on main stem; branches absent (or rarely a few on old or damaged plants); aerial stems evergreen; cones mostly pointed with bristle tip....2
2C. Aerial stems stout as a pencil, more than 1.5 feet tall, dark blue-green, more than 14 vertical ridges; tubercules on stem ridges (feels rough with vertical fingernail scratch); sheaths grey between two black bands, teeth mostly missing....E.hyemale
2B. Aerial stems erect, less than 4mm diameter, to 1.5 feet tall, up to 12 vertical ridges; teeth with white margins....E.variegatum
2A. Aerial stems twisted, less than 1 ft., less than 0.6 mm diameter, up to 6 ridges; no central cavity....E.scirpoides
1A. Stomates in bands or scattered, difficult to see; branches present or not; aerial stems deciduous; cones mostly rounded....3
3B. Branches present to top of stem, first segment longer than stem sheath....4
4C. Most branches forked; main stem sheaths orange, with teeth adhering into 3 or 4 groups.....E.sylvaticum
4B. Branches more than 15, coarse (more than 1 mm. diameter), often ascending, with 3 or 4 sharp ridges; plants common; branch sheath teeth attenuate, spreading; plant dimorphic with fertile stem entirely brown, spring ephemeral....E.arvense
4A. Branches fewer than 15, delicate, less than 1 mm diameter, spreading; siliceous spines projecting from stem (mostly below nodes on upper part of stem), branches unforked; main stem sheaths green, teeth black and separate; branch sheath teeth deltate, clasping; plants uncommon....E.pratense
3A. Branches absent, or if present, not to top of stem, first segment shorter than sheath....5
5B. Stem collapses when pinched at internode; sheaths not much taller than wide, more than 11 teeth per sheath; branches with angular ridges and valleys....E.fluviatile
5A. Stems firm; sheaths twice as tall as wide, less than 11 teeth per sheath; branches with rounded ridges and valleys....E.palustre
The above is based on a key by Don Lubin at nefern.info
1B. Horsetails (subg. Equisetum) have branches, in regular whorls, giving them a somewhat bushy look.
2C. Branches forked; sheath teeth reddish and papery....E.sylvaticum, Wood Horsetail.
2B. First branch segment at the stem is noticeably shorter than the remaining segments.
3B. Stem has a very thin wall with a very large hollow in the center, stem collapses when pinched at internode; usually growing in water; more than 11 sheath teeth per joint, black throughout or with narrow white margins....E.fluviatile, Water Horsetail.
3A. Stem firm when pinched; stem joints appear elongated; less than 11 sheath teeth, with prominent white margins and dark centers; found near, but not actually in, water....E.palustre, Marsh Horsetail.
2A. First branch segment at the stem is actually longer than the stem segment from which it emerges.
4B. Branches are three-sided and horizontal to drooping; uncommon....E.pratense, Meadow Horsetail.
4A. Branches are four angled and vigorously ascending....E.arvense, Field Horsetail.
1A. Scouring Rushes (subg. Hippochaete) lack branches or, when branches are present, they are few and very irregular.
5B. Stems are very slender less than 1 mm diameter, low growing, twisted and tangled rather than upright....E. scirpoides, Dwarf Scouring Rush.
5A. Stems upright upright, more than 18 inches tall.
6C. Stem joints are marked by a narrow, black band; stems smooth and sheath teeth tiny or absent; absent in New England....E.laevigatum, Smooth Scouring Rush.
6B. Stem joints are marked by an ashy grey band; stem rough textured, dark blue-green....E.hyemale, Common Scouring Rush. The stems will be rough textured.
6A.Stem joints are marked by a distinct white margin; stem ridges minutely grooved and sheath teeth persistent....E.variegatum, Variegated Scouring Rush.
The above is based on a key by Earl Rook
Errors, suggests or a key you wish to have posted or adapted for posting? Contact Jeff at info@DigitalNaturalist.info.
last update 2022-Jan-26