Equisetum arvense L.
Standardized Common
Name: Horsetail
Other Common Names: Common Horsetail,
Field Horsetail, Joint Grass
Family: Equisetaceae
Taxonomy: Equisetum is a pteridophyte
(non-seed plant) genus of about 15 species, found nearly worldwide.
Hybridization among similar species is not uncommon; E. ×litorale Kühlewein ex
Ruprecht, a hybrid between E. arvense
and E. fluviatile, occurs throughout
northern North America. Equisetum arvense
is extremely variable in gross morphology; Hauke (1966) estimates that over 200
infraspecific taxa have been described. However, the features that distinguish
these supposed varieties or forms are often under environmental control, so
that multiple forms may appear in a single individual.
Description: Perennial,
rhizomatous herb with jointed stems branching at the nodes; leaves whorled,
reduced to a sheath surrounding the nodes. Reproductive stems and vegetative
stems generally separate; reproductive stems brown, unbranched, short-lived,
with rounded cones at apex; cones borne on vegetative stems in occasional
abnormal plants. Vegetative stems 2–100 cm tall, 0.8–4.5 mm in diameter;
internodes 1.4–4.5 cm long, with 4–16 ridges separated by valleys; in
cross-section hollow, with central canal 1/3–2/3 diameter of stem (reduced in
small stems), with large hollow spaces (vallecular canals) beneath valleys and
small carinal canals beneath ridges, closer to central canal. Leaf sheaths on
stems squarish in face view, 2–5(–10) mm high, 2–5(–9) mm broad; teeth 1–3.5 mm
long, dark, narrow, often cohering in pairs. Branches in regular whorls at most
nodes, ascending, solid, 3–4-ridged, with first internodes longer than the
subtending stem sheaths; sheath teeth attenuated.
Parts
in Commerce:
Vegetative stems
Identification:
- First
internode of each branch, except at the lowest nodes, longer than the
subtending stem sheath
- Branches
solid, lacking central cavity
- Branches
occur in regular whorls on most or all of stem, not confined to midstem or
lower part of stem
- Branches
3–4-angled, normally not further branched
- Stem
sheath teeth (4–)8–10(–16), usually under 4 mm long, dark (not reddish),
narrow, stiff (not papery), often cohering in pairs
- Branch
sheath teeth attenuate (not broadly triangular)
Adulterants: E. arvense may be confused with other species of Equisetum. It is particularly important
that E. arvense be distinguished from
E. palustre L., as the latter species,
which has been found as a contaminant of the former, is toxic when consumed by
livestock. Differences between the two include:
|
|
Equisetum arvense
|
Equisetum palustre
|
|
Number
of stem ridges and stem sheath teeth
|
(4–)8–10(–16)
|
4–10
|
|
Position
of branch whorls on stem
|
Regular
whorls along whole length of stem
|
Only
at midstem nodes; other nodes lacking branch whorls
|
|
Length
of first internode of each branch
|
Longer
than subtending stem sheath
|
Shorter
than subtending stem sheath
|
|
Branch
ridge number
|
3–4
|
4–6
|
|
Central
cavity of branches
|
Absent;
branches solid
|
Present
(observe near base of branches)
|
|
Stem
sheath teeth
|
Dark
with inconspicuous light margins; often cohering in pairs
|
Dark
with conspicuous white, membranous margins
|
|
Branch
sheath teeth
|
Lanceolate-attenuate
|
Triangular
|
References:
Hauke
RL. A systematic study of Equisetum
arvense. Nova Hedwigia. 1966;13:81–109.
Hauke
RL. A taxonomic monograph of Equisetum
Subgenus Equisetum. Nova Hedwigia.
1978;30:385–455.
Hauke
RL. Equisetaceae. In: Flora of North America Editorial Committee, eds. Flora
of North America, vol. 2. New York, NY: Oxford University Press;
1993:76–84.
Figure 25: a–d, Equisetum arvense; e–g, Equisetum
palustre.
