Juncus compressus (Round-fruited Rush)

Plant Info
Also known as: Flattened Rush, Compressed Rush
Genus:Juncus
Family:Juncaceae (Rush)
Life cycle:perennial
Origin:Eurasia
Status:
  • Weedy
Habitat:sun; moist to wet disturbed soil; roadsides, ditches, farm fields, fence rows
Fruiting season:July - August
Plant height:8 to 30 inches
Wetland Indicator Status:GP: FACW MW: OBL NCNE: FACW
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: 6-petals Cluster type: panicle

[photo of panicle] 5 to 60 flowers in a loose to congested branching cluster at the top of the stem, the cluster longer than wide, the branches mostly erect to ascending, the lower branches subtended by an erect, leaf-like bract that usually over-tops the cluster. Flowers are single at branch and branchlet tips, not in heads, have 6 tepals (petals and similar sepals) in 2 layers, both 1.7 to 2.7 mm long and rounded at the tip, brown to dark chestnut brown with a green midrib and white, papery edging. Flowers have a 3-parted style and 6 stamens, the anthers (tips) slightly longer than the filament (stalk).

Leaves and stems: Leaf attachment: alternate Leaf attachment: basal Leaf type: simple

[photo of auricle and channeled leaf] A flowering stem has 1 or 2 alternate leaves and 0 to 2 basal leaves. Leaves are 2 to 14 inches long, up to 2mm wide, flattened and often channeled, and lacking cross partitions (septa). The sheath is open at the front. At the tip of the sheath is a pair of lobes (auricles) .3 to .5 mm long, rounded at the tip with a membranous band around the edge. Stems are smooth, erect, unbranched except in the flower cluster, forming dense clumps and colonies from short, creeping rhizomes.

Fruit: Fruit type: capsule/pod

[photo of achenes and open capsules] Fruit is a 3-sectioned capsule 2.5 to 3.5 mm long, longer than the tepals, oval to nearly round and rounded at the tip, maturing to dark chestnut brown. Inside are numerous seeds, elliptic to crescent-shaped, narrowed at the tip, .3 to .5 mm long, maturing to dark golden brown, and with many vertical ridges and numerous cross-bars.

Notes:

Round-fruited Rush is the only non-native Juncus species in Minnesota at this time, found mostly in northwest Minnesota along roadsides and in ditches and fields. It is salt tolerant and thrives along salted roadsides. It is distinguished from other rushes primarily by the flowers being single rather than in heads of 2 or more, the flattened or channeled leaves, and capsules that are oval to nearly round and longer than the tepals. J. compressus most closely resembles the native Juncus gerardii, a species only recorded once in MN in 1950, which differs by anthers much longer than the filaments, capsules about as long as the tepals, and the lowest bract rarely over-tops the cluster.

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More photos

Photos by K. Chayka and Peter M. Dziuk taken in Kittson and Pennington counties.

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