Juncus stygius (Bog Rush)
|Also known as:||Moor Rush|
|Habitat:||part shade, sun; wet; fens, bogs, peatlands|
|Fruiting season:||July - September|
|Plant height:||4 to 12 inches|
|Wetland Indicator Status:||GP: OBL MW: none NCNE: OBL|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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1 or 2 compact clusters, rarely 3, each about 1 cm (3/8 inch) long, the terminal cluster stalkless and the lateral cluster(s) well separated on short, erect stalks. At the base of each cluster is a scale-like bract that is about as long as or a little longer than the cluster. Each cluster has 1 to 4 stalkless flowers, usually 2 or 3.
Flowers have 6 tepals (petals and similar sepals) in 2 layers, each 3.5 to 5 mm long, translucent whitish or straw-colored to purplish, all about the same length and pointed at the tip, the inner tepals slightly broader than the outer. Flowers have 6 stamens, the anthers (tips) to .5mm long and the filament (stalk) 3 to 4 mm long. In the center is a pale, bullet-shaped ovary with a feathery 3-parted style at the tip.
Leaves and stems:
A flowering stem has 1 to 3 basal leaves and 1 or 2 stem leaves, usually 1 above the middle of the stem. Leaves are 3 to 7 inches long, .5 to 1mm wide, less than half as long as the flowering stem, round to slightly flattened in cross-section. The sheath is open at the front. At the tip of the sheath is a pair of small, rounded lobes (auricles) that barely extend above the leaf base.
The tepals persist and are mostly erect in fruit. Fruit is an oblong-elliptic, 3-chambered capsule 5.5 to 9 mm long, greenish to light brown when mature, pointed at the tip, and much longer than the tepals when mature. Inside the capsule are spindle-shaped seeds, the body .8 to 1.1mm long, yellowish to brown when mature with a thickened appendage (tail) at each end that is slightly longer than the body.
Juncus stygius is a circumboreal species, with one variety native to Europe (var. stygius) and one in North America (var. americanus), which has a somewhat scattered distribution in Canada and barely reaches into the US from northern Maine to northern Minnesota. It is considered rare throughout its limited US range, currently listed as Special Concern in Minnesota and Endangered in Wisconsin. Its preferred habitat is the acidic soil of peatlands, fens and bogs, where it is mostly found in wet depressions and the margins of bog ponds. According to the DNR, its preferred habitat is most sensitive to changes in hydrology, even water diversion from miles away, but climate change and invasive species are also among threats to our limited populations. It should not be confused with any other Juncus species. The few-flowered, 1 or 2 compact heads, nearly white tepals, capsules much longer than the tepals, and very slender appearance distinguish it from other species. At a casual glance it somewhat resembles Rhynchospora alba (White Beakrush), which has more densely flowered clusters, leafier stems, sheaths are closed not open, floral bracts are more leaf-like not scale-like, and the flowers produce a single seed not a capsule.
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Photos by K. Chayka and Peter M. Dziuk taken in Lake County.
Have you seen this plant in Minnesota, or have any other comments about it?