Flower:

Branching cluster at the top of the stem, the branches ascending to spreading with numerous flowers, the cluster compact or open and loose. The cluster is subtended by an erect bract that is round in cross-section and appears to be a continuation of the stem, with the cluster erupting from the side of the stem. The bract is several times longer than the cluster and up to 1/3 as long as the stem.

Flowers are numerous, single, not in heads of 2 or more, on stalks of varying lengths, with 6 tepals (petals and similar sepals) in 2 layers, 1.9 to 3.5 mm long, the inner and outer tepals about equal in shape, sharply pointed at the tip, and the inner tepals slightly shorter than the outer. Tepals are green along the midrib with a light to medium brown stripe along either side and translucent, white papery edging. Flowers have a 3-parted style and 6 yellow stamens, the anthers (tips) about as long as the filament (stalk).

Leaves and stems:

A flowering stem has no leaves to speak of, just one to several bladeless sheaths at the base. Sheaths are reddish to brown at the base and green to brown above. Stems are medium green, round in cross-section, smooth but with numerous longitudinal ridges, erect, unbranched, and create dense clumps from short rhizomes.

Fruit:

The tepals persist and become light brown and slightly spreading in fruit. Fruit is an oval-elliptic, 3-chambered capsule 1.5 to 3.2 mm long, brown when mature, as long as or slightly shorter than the tepals, rounded at the tip, sometimes with a minute beak at the top. Inside the capsule are numerous tiny seeds, about .5mm long, amber colored when mature, with no elongated tails.

Notes:

Juncus effusus is a circumpolar species, native to much of North America as well as Europe and Asia. There are 4 Juncus species in Minnesota that have a lateral cluster with the bract appearing to be a continuation of the stem. Of these, most similar is Juncus pylaei, which was once treated as a variety of J. effusus (var. pylaei) and is found in essentially the same habitats and geographical range within Minnesota. The most consistent difference between them is the number of vertical ridges on the stem, best seen just below the flower cluster, J. pylaei having 25 or fewer fairly distinct ridges and J. effusus having 25 or more ridges that are fairly inconspicuous until after drying.

The other species in Minnesota with lateral flower clusters, Juncus balticus and Juncus filiformis, are not clump-forming but rhizomatous, forming colonies, and are typically fewer flowered. Juncus balticus also has tepals that are often dark purplish brown with a green midrib and white edging, and larger fruits (3.5 to 4.5mm long); Juncus filiformis has a nearly round capsule and its bract is much longer, often longer than the stem. The taxonomy for some Juncus species is a bit confusing, including this one. USDA lists 9(!) varieties of Juncus effusus, BONAP lists 4 subspecies, the most common of which is subsp. solutus and is the subspecies found in Minnesota. The vars/subsp are not well documented so distinguishing characteristics are unclear (to us).