Description: This native
perennial plant produces fertile and infertile shoots that are deciduous. Each
fertile shoot is unbranched and about 4-6" tall. It has a central stalk that is
light brown to brown and about ¼" across in diameter. This stalk
terminates in a spore-bearing cone up to 1" long; the cone is oblongoid in
shape and rounded at the top. The surface of the cone is mostly brown, but it
is covered with spore-bearing tubercles that have black and white markings. The
fertile shoots develop during mid-spring, but soon wither away after the cones
have released their spores. The infertile (or vegetative) shoots have a very
different appearance. They develop during late spring and persist until the
fall. The infertile shoots are ½–2' tall; they have whorls of
branchlets along at least the upper half of their stems. The stems and
branchlets of these shoots are slender and green. Each central stem consists of
several joints; at the apex of each joint (except the uppermost), there is a
short sheath with 3-4 teeth along its upper rim. This sheath is appressed to
slightly spreading and green to brown. The base of the next joint develops from
this sheath. Each joint is terete with 10-14 ridges along its length; sometimes
there are more or fewer ridges. Initially, the branchlets are similar to the
central stems, except they are much smaller in size. Later, they become almost
as long as the stems. At this stage, the infertile shoots resemble small
conifers because of the long needle-like branchlets. The branchlets have joints
with sheaths like the stems, but there are only 3-4 teeth along the upper rim
of each sheath. Usually, these branchlets are unbranched, but sometimes they
produce secondary branchlets. An infertile shoot may produce a small infertile
cone at its apex, but this is very unusual. Both the stems and branchlets of
Common Horsetail are mostly solid. The root system consists of long rhizomes
and secondary fibrous roots. This plant often forms colonies.
Cultivation: The preference is full or partial sun
and moist to mesic conditions. Different kinds of soil are readily tolerated,
including those containing sand, gravel, and fertile loam. This plant spreads
readily by its rhizomes and can be very aggressive. It is possible to eliminate
a vegetative colony by spreading a black plastic sheet across the entire area
where it occurs. This sheet should remain in place for at least a year.
Range &
Habitat: Common Horsetail is found in every county of Illinois and
is quite common (see
Distribution
Map). Habitats include savannas, sandy savannas, black soil prairies, sand
prairies, gravel prairies, dolomite prairies, thickets, fens, seeps, ditches,
roadsides, areas along railroads (including the gravel ballast), old fields,
and waste areas. This plant is often found in degraded areas and is rather
weedy; however, it also occurs in higher quality habitats, especially where the
soil is rather sandy or gravelly.
Faunal
Associations: Where it occurs in dense colonies, Common Horsetail
provides cover for small mammals and birds. The coarse stems are not often
eaten by mammalian herbivores because of their silica deposits; these stems are
also somewhat toxic because thiamin-deficiency can result if they are eaten by
the same animals. Overall, the ecological value of this plant to wildlife is
low.
Photographic Location: The
photograph of the infertile shoot was taken near a railroad in Urbana,
Illinois, while the photograph of the fertile shoot was taken at the
webmaster's apartment complex in the same city.
Comments: This odd little plant is the most common
and weedy horsetail in Illinois. The cone-bearing fertile shoots resemble brown
mushrooms (something like the morel mushroom), while the infertile shoots look
like small conifers during the summer. Few people realize that both types of
shoots are produced from the rhizomes of the same plant. Common Horsetail
differs from other horsetails by its brown fertile shoots, which lack
chlorophyll. Other Equisetum spp. (Horsetails) in Illinois produce green
fertile shoots that are similar to infertile shoots in appearance. The whorled
branchlets of Common Horsetail can become almost as long as the central stem
– they are produced in great abundance and often obscure the central
stem's visibility by the beginning of summer. Other Horsetails produce
branchlets that are much shorter than their stems, or they produce no
branchlets at all. There are other technical differences between Common
Horsetail and other Horsetails, but it is usually easy to identify in the
field.