Rhynchospora alba (White Beakrush)

Plant Info
Also known as: White Beaksedge
Genus:Rhynchospora
Family:Cyperaceae (Sedge)
Life cycle:perennial
Origin:native
Habitat:sun; wet; fens, bogs, peatlands, floating mats
Fruiting season:July - October
Plant height:6 to 20 inches
Wetland Indicator Status:GP: OBL MW: OBL NCNE: OBL
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: indistinct Cluster type: round Cluster type: spike

[photo of spikelet clusters] 1 to 3 inverted cone-shaped to hemispheric clusters at the tip of the stem, each 1 to 2.5 cm (3/8 to 1 inch) across, usually with 1 or 2 smaller, lateral clusters widely separated on the upper half of the stem. Each cluster is on an erect stalk with a leaf-like bract at the base, the bract about as long as or a little longer than the attending cluster. Each cluster has several to many spikelets (flower clusters).

[close-up of spikelets just past flowering] Spikelets are stalkless to short-stalked, 3.5 to 5.5 mm long (1/8 to ¼ inch), narrowly elliptic, pointed at the tip, with 2 or 3 perfect flowers (both male and female parts), each subtended by a scale; the lowest scale is often empty. Flowers have 3 stamens and a 2-parted style. Scales are 3 to 4 mm long, 1.4 to 2.5 mm wide, lance-shaped, pointed at the tip, tightly appressed and overlapping, white turning pale brown with maturity.

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

[photo of stem, sheath and flat leaf base] Leaves are alternate, erect to ascending, hairless, flat at the base, 3-sided at the tip, .5 to 2.5 mm wide, shorter than the flowering stem and the upper leaves usually not overtopping the terminal cluster. Sheaths are closed, more or less straight across at the tip, translucent green and membranous on the front. Stems are slender, erect, unbranched, round to weakly 3-sided in cross-section, hairless, green, leafy, and multiple from the base usually forming dense clumps.

Fruit: Fruit type: seed without plume

[photo of mature spikelet, scale and achene] Spikelets turn brown at maturity and produce 1 or 2 seeds (achenes), the body 1.5 to 2 mm long, flattened lens-shaped, oval in outline but widest above the middle (obovoid), the persistent style forming a narrowly triangular beak .5 to 1.2 mm long, and tapering at the base to a stalk-like appendage (stipe).

[photo of achene with perianth bristles] Surrounding the base are 9 to 12 barbed bristles all more or less equal in length and about as long as or slightly longer than the achene, including the beak, the barbs downward pointing or occasionally absent altogether, and the bristles often minutely hairy towards the base.

Notes:

Rhynchospora alba is a common sedge of the open, acidic soils of peatlands, fens, bogs, floating mats and conifer swamps, often forming colonies. The whitish spikelets really stand out. At a casual glance it is similar to the rare Juncus stygius, which has open sheaths not closed, only 1 to 4 flowers in a cluster, flowers with 6 tepals (petals and similar sepals), and fruit is a multi-seeded capsule. When flowering, Eriophorum virginicum (Tawny Cottongrass) also bears a resemblance, but is distinguished by longer and broader leaf-like bracts, the longest 4+ inches, and more strongly 3-sided stems especially the upper stem.

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More photos

Photos by K. Chayka taken in Lake County. Photos courtesy Peter M. Dziuk taken in Anoka and Lake counties.

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