Equisetum Key

New England Equisetum Key

1. 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

1'. Stomates in bands or scattered, difficult to see; branches present or not;

aerial stems deciduous; cones mostly rounded. → 3

2. Aerial stems stout as a pencil, >1.5 feet tall, dark blue-green, >14 vertical ridges;

tubercules on stem ridges (rough to vertical fingernail scratch);

sheaths grey between two black bands, teeth mostly missing – E. hyemale

2'. Aerial stems erect, ≤4mm diam., to 1½ ft. tall, ≤ 12 vertical ridges;

teeth with white margins – E. variegatum

2". Aerial stems twisted, <1 ft., <0.6mm diam., ≤6 ridges; no central cavity – E. scirpoides

3. Branches present, to top of stem, first segment ≥ stem sheath → 4

3'. Branches absent, or if present, not to top of stem, first segment < sheath → 6

4. Branches more than [15?], coarse (>1 mm. diam.), 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

4'. Branches fewer than [14?], delicate (<1mm diam.), spreading;

siliceous spines projecting from stem (mostly below nodes on upper part of stem) → 5

5. Most branches forked; main stem sheaths orange, with teeth adhering into 3 or 4 groups. – E. sylvaticum

5'. Branches unforked; main stem sheaths green, teeth black and separate;

branch sheath teeth deltate, clasping; plants uncommon – E. pratense

6. Stem collapses when pinched at internode; sheaths not much taller than wide,

>11 teeth per sheath; branches with angular ridges and valleys – E. fluviatile

6'. Stems firm; sheaths twice as tall as wide, <11 teeth per sheath;

branches with rounded ridges and valleys – E. palustre