Juncus marginatus (Grassleaf Rush)

Plant Info
Also known as: Marginated Rush
Genus:Juncus
Family:Juncaceae (Rush)
Life cycle:perennial
Origin:native
Status:
  • State Endangered
Habitat:part shade, sun; moist;
Fruiting season:August - September
Plant height:10 to 20 inches
Wetland Indicator Status:GP: FACW MW: FACW 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 flower heads] 5 to 50(200) flower heads in a branching cluster at the top of the stem, the heads at branch tips, the branches erect to ascending and subtended by an erect, scale-like bract shorter than the branch. The bract of the lowest branch is leaf-like and usually longer than the branch, sometimes overtopping the terminal cluster. Each flower head is up to 10 mm in diameter, inverted cone-shaped to nearly hemispheric, with 3 to 10+ erect to ascending flowers.

[close-up of flower heads] Flowers have 6 tepals (petals and similar sepals) in 2 layers, the outer tepals 1.8 to 3.2 mm long and pointed or abruptly tapering to a tail-like tip, the inner tepals slightly shorter and blunt or pointed at the tip, both brown with a broad green midstripe, and translucent whitish to light brown edging. Flowers have a 3-parted style and 3 stamens, the anthers (tips) up to half as long as the filament (stalk). At the base of each flower is an appressed, papery bract, sharply pointed or tapering to a tail-like tip and mostly shorter than the tepals (excluding the tail).

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

[photo of auricle and flat leaf blade] A flowering stem has 2 to 5 basal leaves and 1 to 3 alternate leaves on the lower stem. Leaves are 4 to 12 inches long, 1 to 5mm wide, flat, the stem leaves shorter and narrower than the basal leaves and all shorter than the flowering stem. The sheath is open at the front. At the tip of the sheath is a pair of lobes (auricles) .5 to 2 mm long, rounded at the tip. Stems are smooth, erect, unbranched, slightly flattened in cross-section, swollen and sometimes bulbous at the base, single or few from the base, sometimes forming loose clumps from short, knotty rhizomes.

Fruit: Fruit type: capsule/pod

[photo of fruit] Fruit is a 3-sectioned capsule, glossy brown when mature, sometimes speckled red, as long as or slightly shorter than the tepals, oval to nearly round. Inside are numerous seeds, .4 to .7 mm long, yellowish to amber-colored when mature, narrowly elliptic to spindle-shaped, narrowed at both ends but lacking distinct tails, and with network of fine ridges across the surface.

Notes:

Juncus marginatus is one of the rarest Juncus species in Minnesota. The first record was from southern Anoka County in 1917 but a second population was not discovered for another 82 years. According to the DNR, when the original population was destroyed in 1960, it was feared extirpated from the state and was subsequently listed as a Special Concern species in 1996. A few years later, the second Anoka County population was discovered and, more recently, a third site in Morrison County. The species was elevated to Endangered in 2013. The DNR's MNTaxa data currently lists it as present Ramsey County but there is no additional information on that population. Since the Anoka and Morrison populations are on state lands, it is hoped management practices will ensure the long-term survival of this species in Minnesota.

Some references describe the species as reaching 40+ inches in height with up to 200 flower heads in a cluster. That may be true to our south or east where this species is more common, but in Minnesota it rarely exceeds 20 inches and typically has fewer than 50 heads. It grows together in the same wetland habitat as other, more common Juncus species including J. canadensis, J. brevicaudatus, J. torreyi and J. vaseyi, all of which have leaves that are round or channeled in cross-section where J. marginatus leaves are flat. The tepals of J. marginatus are somewhat similar to J. longistylis, but the latter are about twice as large (5 to 6mm long) and is found primarily in western MN.

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More photos

Photos by K. Chayka taken in Anoka County.

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