Flower:

3 to 30 (rarely more) flower heads in a branching cluster at the top of the stem, the cluster as long as or longer than wide, the branches erect to ascending to spreading, the lower branches subtended by an erect, leaf-like bract that does not overtop the cluster. Each flower head is 6 to 8 mm in diameter with 3 to 10 flowers, inverted cone-shaped to hemispheric in outline. Flowers have 6 tepals (petals and similar sepals) in 2 layers, both 1.8 to 3 mm long and pointed at the tip, green to straw-colored to dark chestnut brown with white, papery edging. Flowers are stalkless, have a 3-parted style and 6 stamens, the anthers (tips) as long as the filament (stalk).

Leaves and stems:

A flowering stem has 3 to 6 (rarely fewer) alternate leaves and 0 to 2 basal leaves. Leaves are 1 to 4¾ inches long, up to 1.1mm wide, round in cross-section, with cross partitions (septa) at regular intervals (may be easier felt than seen). The sheath is open at the front. At the tip of the sheath is a pair of lobes (auricles) .5 to 1 mm long, rounded at the tip with a membranous band around the edge. Stems are smooth, unbranched except in the flower cluster, erect or sometimes prostrate but rising at the tip (decumbent), or floating when in standing water. Plants form colonies from creeping rhizomes and may form tight clumps.

Fruit:

Fruit is a 3-sectioned capsule 2.8 to 4 mm long, extending about 1 mm beyond the tepals, tapering to a pointed tip, maturing to dark chestnut brown. Inside are numerous oval seeds, .5 mm long, maturing to dark golden brown, and with a faint, wrinkly texture.

Notes:

Jointed Rush is a very rare species in Minnesota, first recorded on the sandy shore of White Bear Lake in Ramsey County in 1926 and not seen again until 1998 in northern Aitkin County on another sandy shore. The original White Bear Lake population is presumed destroyed and only 3 other records currently exist in the state, and, according to the DNR, populations are at extreme risk due to lakeshore development and recreational activities. It was listed as an Endangered species in 2013. In its broader range, it is typically found in sandy, calcareous soils along shores, stream banks, bogs and in wet meadows.

Juncus articulatus most closely resembles 2 other Juncus species in Minnesota: Juncus brevicaudatus and Juncus alpinoarticulatus. The tepals and capsules are all slightly different between the three, with J. brevicaudatus capsules and tepals both longer, proportionately narrower and all tapering to sharply pointed tips, J. articulatus capsules and tepals also all tapering to pointed tips though proportionately broader than J. brevicaudatus, and J. alpinoarticulatus capsules more distinctly rounded at the tip, the inner tepals usually blunt to rounded, and the capsule not extending more than .5mm beyond the tips of the tepals, where the other two both extend about 1mm. J. brevicaudatus is also distinguished by its seed with a distinct elongated “tail” at each end, which the other two lack. The non-native Juncus compressus is somewhat similar, but its flowers are all single at branch tips, not in heads of 2 or more, and is usually found in the disturbed soils of roadsides, ditches and fields.