Common Rush

Juncus effusus
Wednesday, July 11, 2012

           Grass-like plants that make their home in aquatic or wetland environments can be fairly difficult to distinguish. However, the difference between grasses, sedges, and rushes is relatively straightforward. Sedges have edges (most sedges have distinctly triangular-shaped stems, although their leaves can be flat) and rushes are round (almost all rush stems are cylindrical in shape). On the other hand, if both the stem and leaves of the plant are flat, it is very likely to be a grass. A further test would reveal that grasses are hollow on the inside—that is, the center of their stem is open—whereas sedges and rushes are both solidly fleshy.

           This rush is unusual because of its lack of anything that might be considered to be a leaf, or even of nodes indicating their absence. The base of each stem is covered by a dark basal sheath. From the base, the stem continues for up to a meter before terminating in an inflorescence. Although it appears that the stem continues for 10-30 centimeters more after the inflorescence, this is, in fact, merely a modified bract of the flower that resembles the stem. The inflorescence is in the shape of a compound umbel (having many flower stalks that further divide into more stalks, ending with flowers; see right). The “rays” on this inflorescence can be either bunched together or widely spreading, and the entire inflorescence tends to droop from one side of the rush. When the inflorescence is young, it is green in color and the flower buds are in tight balls. As it ages, the color changes to yellowish and then to dark brown, while the flowers open in the summer. The flowers themselves are 3-parted, having three sepals, three petals, three stamens, and one style. They are not showy, and, indeed, the petals merely resemble inner sepals. The wind is responsible both for cross-pollination and for dispersing the tiny seeds when the 3-parted seed capsules split open. The seeds are also capable of floating on the water until they reach a suitable new habitat.

           This rush has a massive range. Native to Europe, Asia, North America, Australia, and New Zealand, it truly earns its Latin name effusus. It prefers damp, swampy ground, and can also be found growing in the shallow water of ponds, slow streams or rivers, or other bodies of water. However, it is relatively tolerant of dry conditions or degradation of its aquatic habitat. It prefers to be located in full sun, but, again, can tolerate some shade. It typically grows in clumps in swampy environments. Once it has been well established in a location, it will spread via its rhizomes and form new clumps in the surrounding area.     

           This rush has multiple human uses. In Japan, it is grown commercially for the weaving of tatami—split rush mats for homes. It has also been used historically to make “rushlights,” created by peeling away the outer layers of the rush, drying it, and soaking it in fat or wax. When it was dry, a rushlight could be used as an inexpensive candle.  

           These rushes were collected from the edge of the station pond, where a few clumps grow partially submerged in the water. They can also be found in the swampy area near Schoew, and elsewhere on the station.

Hazel Galloway