Hippuris vulgaris / common mare’s tail
- two possible forms – emergent and submerged
- submerged looks like a tail… thick with whorls of long-ish leaves
- emergent looks like Equisetum gone wild… whorls of many leaves
- both forms may be present
- mostly in river backwaters or small streams running through the fen
Common mare’s tail is a creeping, perennial herb, found in shallow, preferably non-acidic waters and mud flats. Mare’s tail has unbranched stems, abundant whorled leaves (especially under water) and inconspicuous flowers (at best). The plants may either be submerged or emergent (or both) and their form depends on that.
Underwater plants have limp stems and leaves that are very long (as in the gallery photos). These leaves often appear reddish. Emergent portions of the plants are stiff and erect and the leaves are much shorter and narrower, giving the usually-plentiful stalks a “bottle brush” appearance. That has, historically, caused confusion, suggesting that the plant is actually an Equisetum. In all cases, the stems are hollow and unbranched.
In the Valley, mare’s tail occurs mostly in backwaters or small streams running through the fen.
Regardless of shoot form, mare’s tail roots underwater, even if it’s 10 feet deep. It forms large colonies by thick, creeping rhizomes. This is the only form of spreading for fully submerged plants, but emersed plants also produce seeds. The roots form at stem nodes (see gallery photo).
Mare’s tail leaves occur in whorls of 6–12; under water whorls are quite closely spaced and responsible for the mare’s tail look. In all cases, the leaves are entire. Emerged leaves are whorled in groups of 8-12. They are also smooth-edged and hairless. They have pointed tips and no petioles.
Only emergent plants can flower, and not all do. But if they do, flowers are really inconspicuous and in the leaf axils of middle and upper leaves.
Interesting bits – Apparently, mare’s tail can be a serious methane emitter because of its deep roots. They extend well into the muck–to the anoxic zone–where methane is produced, and served as a conduit for the gas through to the atmosphere.
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