Description: This native perennial plant is about 1½–3' long. It consists of a central stem that is erect or semi-erect; this stem often has whorls of 2-6 branchlets along the upper half of its length, otherwise it is unbranched. The central stem has about 15-25 fine ridges along its length; it is green to dark green. The stem diameter is up to 1/3" across; it has a very large interior cavity that spans at least 80% of the diameter.
The central stem consists of several
overlapping joints. Each joint is several inches long; its apex consists of an
appressed ring-like sheath, from which the base of the next joint develops.
This sheath is about ¾" in length and green to brownish green; it is
often dark brown or black at the base, while its upper rim has about 18 tiny
teeth that are dark brown or black. However, the sheaths and their teeth become
whitish grey as they age. The jointed branchlets have an appearance that is
similar to the central stem, except that they are smaller. These branchlets
usually spread upward, rather than droop downward; unlike the central stem,
they are always unbranched. The branchlets are hollow and they span a few
inches in length. Each fertile shoot produces a spore-bearing cone that is
about 1" long; this cone is usually rounded at the top and it occurs on a short
stalk. Infertile shoots are similar to fertile shoots, except they lack
spore-bearing cones; both types of shoots are deciduous, rather than evergreen.
The spore-bearing cones are produced during late spring to early summer. After
releasing their spores, they gradually wither away. The root system consists of
extensive rhizomes and fibrous roots. This plant often forms vegetative
colonies.
Cultivation: The
preference is full to partial sun and wet to moist conditions. Different kinds
of soil are tolerated, including those containing sand, gravel, and sphagnum
moss. The pH of the soil can be acidic or alkaline. This plant often grows in
shallow water, although it can tolerate surprisingly dry situations as
well.
Range & Habitat: Water
Horsetail occurs occasionally in the northern half of Illinois, but it is
absent in the southern half of the state. Habitats include marshes, swamps,
bogs, edges of ponds and creeks, sloughs, ditches, and railroad embankments
(including the gravel ballast). This species prefers more aquatic habitats than
most Equisetum spp. (Horsetails).
Faunal
Associations: The value of Equisetum spp. (Horsetails) to
wildlife is limited. Because of the dense colonies that they often form,
Horsetails provide cover for wetland birds and small mammals. Because stems of
Horsetails contain high levels of silica and can cause thiamine-deficiency,
they are rarely eaten by most mammalian herbivores. Moose is an exception, but
this animal doesn't occur in Illinois.
Photographic Location: The gravelly embankment of a
railroad near Champaign, Illinois. This plant was photographed during the
summer, by which time its spore-bearing cones were withering away and its stems
were beginning to display symptoms of old age.
Comments: The webmaster was surprised to find
several colonies of this wetland plant growing on the gravelly embankment of a
railroad. For some reason, Horsetails often do this, even though this type of
habitat is supposed to be too dry for them. Water Horsetail is a rather slender
and medium-sized Equisetum sp. that produces small whorls of branchlets
in the upper half of its stems. It is smaller than Equisetum hyemale var.
affine (Scouring Rush), but larger than Equisetum arvense (Field
Horsetail). Field Horsetail also produces whorls of branchlets along its stems,
but its branchlets are more abundant and they eventually become almost as long
as the central stems. The branchlets of Water Horsetail are less abundant and
they are always much shorter than the central stems. Water Horsetail resembles
Equisetum palustre (Marsh Horsetail), Equisetum pratense (Meadow
Horsetail) and Equisetum sylvaticum (Woodland Horsetail), but its stems
are more hollow. The interior cavity of these latter species spans less than
50% of the diameter of their stems.