Equisetum arvense is our most common species of horsetail.
The stems are erect and usually bear many branches in whorls.
There are conspicuous sheaths at the nodes, above the whorled
branches, giving the stems a somewhat "jointed" appearance.
In our other species of Equisetum the spores are produced
in a cone-like strobilus at the tip of the stem, but in Equisetum
arvense the spores are produced by a separate
fertile stem that is brown rather than green and is much shorter
than the non-flowering green stems. Both fertile and sterile stems
arise from wide-ranging, horizontal, underground stems called
rhizomes. The rhizomes provide a means of rapid spread in much
the same way that quack-grass spreads in gardens and Equisetum
arvense can be an aggressive invader of sunny sites.