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Eriophorum vaginatum L. var. spissum (Fernald) B. Boivin

Eriophorum spissum Fernald

Eriophorum spissum Fernald var. erubescens (Fernald) Fernald

Eriophorum vaginatum L. ssp. spissum (Fernald) Hultén

Cotton sedge, hare’s-tail cottongrass, tussock cottongrass, sheathed cottonsedge

KingdomPlantaePlants, but not fungi, lichens, or algae
SubkingdomTracheobiontaVascular plants—plants with a “circulatory system” for delivering water and nutrients
DivisionMagnoliophytaFlowering plants, also known as angiosperms
ClassLiliopsidaMonocots (plants with a single seed leaf); includes the lily family
SubclassCommelinidaeDayflowers and spiderworts, and several others
OrderCyperalesFlowering plants including grasses
FamilyCyperaceaeSedge family
GenusEriophorumWool-bearing
SpeciesvaginatumSheathed, having a sheath
var.spissumFrom Proto-Indo-European “spidtos,” cognate to Ancient Greek σπιδνός (spidnós, “dense, solid”) and Latvian spiedu (“I compress, I press”)

About plant names...

Hare’s-tail cottongrass is a tussock-forming sedge native to North America, with a preference for peaty bogs and acidic wetlands.

Plants: Stems (culms) are round, oval, or triangular in cross section. The stems are very thin, about ¹/₃₂" (0.3 mm), and densely packed into tussocks.

Leaves: There are a few basal, alternate leaves, and a few higher up, but they are easy to miss amongst the many stems. Each leaf is up to ¹/₃₂" (1 mm) wide, resembling a grass blade, and may be nearly as long as the stem.

Flowers: Flowers appear in a compact cluster at the tip of the stem, appearing elliptic at first, then more hemispheric as the plant matures. If you look closely, the numerous flowerheads are arranged in a spiral pattern. The cottony flowerheads are ¾-2" (1.9-5 cm) in size.

Fruits: ¹/₁₆-⅛" (1.9-3.5 mm) long. They are triangular to rounded in cross-section. White bristles around the base of each flower extend in length, becoming ¼-¾" (8.3-19 mm) long, producing the “cotton.” Seeds (achenes) are ¹/₁₆-⅛" (1.9-3.5 mm) long, and shaped like teardrops. They are three-sided when viewed in cross section. The tussocks of narrow stems, white bristles (vs. brownish), and erect (vs. nodding) orientation are identifying features.

These are closely similar:

 

Eriophorum vaginatum (cotton sedge, hare’s-tail cottongrass, tussock cottongrass, sheathed cottonsedge)

7/13/2015 · Mt. Mansfield, Stowe/Cambridge, VT
≈ 8 × 5" (19 × 13 cm) ID is uncertain

Eriophorum vaginatum (cotton sedge, hare’s-tail cottongrass, tussock cottongrass, sheathed cottonsedge)

7/13/2015 · Mt. Mansfield, Stowe/Cambridge, VT
≈ 9 × 6" (23 × 15 cm)

Eriophorum vaginatum (cotton sedge, hare’s-tail cottongrass, tussock cottongrass, sheathed cottonsedge)

7/13/2015 · Mt. Mansfield, Stowe/Cambridge, VT
≈ 12 × 8" (31 × 21 cm)

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Eriophorum vaginatum var. spissum

Eriophorum virginicum

Rhynchospora alba
Common Name

cotton sedge

tawny cottonsedge

white beakrush
Plant Stems (culms) are round, oval, or triangular in cross section. The stems are very thin, about ¹/₃₂" (0.3 mm), and densely packed into tussocks. Stems are not branched, hairless, and 16-48" (40-121 cm) in height. They are single, or in small groups, with round or slightly triangular cross sections. Stems are up to 20" (50 cm) in height, round or oval to weakly triangular (“obscurely triangular,” according to one source) in cross-section. They are not branched and hairless, and are cespitose: often occuring in clumps.
Flowers Flowers appear in a compact cluster at the tip of the stem, appearing elliptic at first, then more hemispheric as the plant matures. If you look closely, the numerous flowerheads are arranged in a spiral pattern. The cottony flowerheads are ¾-2" (1.9-5 cm) in size, erect (vs. nodding) and are white (vs. brownish). Although they often look like a single tuft of cotton, the tuft is comprised of 2-10 densely packed spikelet clusters. The lowermost spikelets are wrapped in leafy bracts, like tiny ears of corn. Each spikelet is ⅛-⅜" (6-10 mm) long. Ten or more threadlike bristles—the “cotton”—extend from the base of each flower. The threads eventually become up to ¾" (2 cm) long, usually brown at the base, and somewhere between off white and brown or red-brown as the plant ages. The red-brown color dis­tinguishes tawny cotton-grass from other cotton grasses. (More subtle identifiers include a single stamen per floret instead of 3, and multiple veins on the scales of the seedheads.) Flowers appear from Jun to Sep. White, rounded clusters of spikelets turn light brown with age. Usually there is a single cluster, but there may be one or two additional clusters. Clusters are ⅜-⅞" (1-2.5 cm) in size, comprised of spikelets that are ⅛-³/₁₆" (3.5-5.5 mm) long, and narrowly elliptic: shaped like miniature ears of corn.
Leaves There are a few basal, alternate leaves, and a few higher up, but they are easy to miss amongst the many stems. Each leaf is up to ¹/₃₂" (1 mm) wide, resembling a grass blade, and may be nearly as long as the stem. Alternate, up to 12" (30 cm) long × ¹/₃₂-⅛" (1.5-4 mm) wide. They are linear, flat at the base, becoming triangular in cross section as they approach the tip, with parallel veins. They may be erect, or floppy. Grasslike leaves are flat at the base, becoming triangular in cross-section toward the end, ~¹/₃₂" (0.5-1.5 mm) in width. Sheaths enclosing blades around the culm are closed.
Fruit ¹/₁₆-⅛" (1.9-3.5 mm) long. They are triangular to rounded in cross-section. White bristles around the base of each flower extend in length, becoming ¼-¾" (8.3-19 mm) long, producing the “cotton.” Seeds (achenes) are ¹/₁₆-⅛" (1.9-3.5 mm) long, and shaped like teardrops. They are three-sided when viewed in cross section. Fruits appear from July to September. The achenes are ¹/₁₆-⅛" (2.5-4 mm) long, shaped like a narrow ellipse with a triangular or rounded cross section. They are brown or black. Achenes are lenticular (“lens-shaped”), ~¹/₃₂" (0.9-1.3 mm) wide, narrowing to a stalk at the base. Each spikelet contains one or two achenes. Mature spikelets are brown. A tangle of 9 to 12 bristles surround the base of each spikelet.
Range/ Zones

USDA Zones: 2-6

Habitats Peaty bogs and acidic wetlands. Wet, peaty, acidic soil, such as bogs, damp meadows, and conifer swamps. Bogs, peatlands, floating mats.
Type Wild Wild Wild

 

 
Rhynchospora colorata

Kyllinga nemoralis
Common Name

starrush whitetop

white water sedge
Plant Grasslike clumps or solitary plants. Each is topped with a “flower” comprised of 3-10 specialized green and white leaves. The “petals” are really specialized leaves (bracts), each up to 5" (13 cm) × ¹/₁₆-¼" (2-7 mm). Stems are triangular in cross section. These perennials spread via creeping rhizomes. Their culms are tufted or spaced, standing straight, up to 22" (55 cm) in height. Like other sedges, the culms are triangular in cross-section.
Flowers A dense cluster of small spikelets ⅛-¼" (5-7 mm) long, nestled amidst the bracts. Each spikelet is white, ovoid, and contains several tiny flowers. They appear in June and July. Flowerheads are roughly spherical, ⅛-⅜" (5-10 mm) around. Usually there is a single flowerhead, but up to three smaller heads may be fused to the largest one. Beneath the flowerhead are 3 or 4 long bracts, grasslike spikes, up to 8" (20 cm) in length.
Leaves Grasslike, linear, arising from the base of the plant in clusters, spreading or erect, ¹/₃₂-⅛" (0.5-3 mm) wide. Grasslike leaves are linear, almost as long as the culms, ¹/₃₂-⅛" (1.5-3 mm) wide. Leaf sheafs are brown or purple-brown.
Fruit Spikelets mature to a yellow to mahogony color. Each spikelet contains several fruits, each ¹/₃₂-¹/₁₆" (1.5-1.7 mm) in size. Fruits appear in late spring to summer.  
Range/ Zones

USDA Zones: 7-10

Habitats Wet coastal areas, dunes, flatwoods, wet prairies, swales and roadside ditches Shaded meadows, rock crevices and along roadsides. Not native to North America, invasive in Hawai’i.
Type Wild Wild

 

Online References:

Eriophorum vaginatum var. spissum at Minnesota Wildflowers

Eriophorum vaginatum var. spissum on Wikipedia

Eriophorum vaginatum var. spissum on gobotany.nativeplanttrust.org

Eriophorum vaginatum var. spissum on plantfinder.nativeplanttrust.org

References:

Arsenault, Matt; Mittelhauser, Glen H.; Cameron, Don; Dibble, Alison C.; Haines, Arthur; Rooney, Sally C.; and Weber, Jill E., Sedges of Maine: A Field Guide to Cyperaceae, University of Maine Press, 2013, p. 606

Eriophorum vaginatum var. spissum description by Thomas H. Kent, last updated 16 Sep 2020.

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