Aquatic and Wetland Vascular Plants of the Northern Great Plains

Juncus L. -- Rush

Tufted or rhizomatous grasslike plants, mostly perennial; culms elongate, simple, erect; rhizomes often strongly developed. Leaves cauline or mainly basal, alternate and usually 3-ranked, reduced to sheathing at the base of the culm in some spp.; blades, if present, terete and often nodulose-septate, or flat to involute; sheaths broader than the blades, commonly with a pair of auricles at the summit. Inflorescence a compact to open cyme of few to many flowers, subtended by 1-few leaflike involucral bracts, the flowers borne singly on pedicels or grouped into glomerules of few to many; each subtended by 1 or 2 bracteoles. Flowers perfect, regular; perianth of 6 chaffy tepals, these green to purplish-brown, persistent, scalelike; stamens 6 or 3; carpels 3, united, stigmas 3, ovary superior, 1- or 3-celled, with parietal or axile placentation, ovules numerous. Fruit a many-seeded, 3-valved and often 3-angled capsule, 1-locular to completely 3-celled; seeds ovoid to oblong, apiculate or with membranous, taillike appendages at both ends.

Reference:

Weigand, K. M.  1900. Juncus tenuis Willd. and some of its
	North American allies.  Bull. Torrey Bot. Club 27:511-527.

Lead	Characteristic	Go To
1	Flowers individually pedicelled, each subtended by a pair of membranous bracteoles; leaves flat to involute or terete and narrowly channeled on the upper side, never septate, or the leaves bladeless, reduced to basal sheaths.	Lead 2
1	Flowers grouped into glomerules of few to many, each subtended by a single bracteole; leaves terete or flat, often nodulose-septate.	Lead 9
2	Leaves comprised of bladeless basal sheaths; involucral leaf erect, resembling a continuation of the culm, the inflorescence appearing lateral.	J. balticus
2	Leaves with blades; inflorescence terminal.	Lead 3
3	Plants annual; inflorescence making up 1/3 or more of the height of the plant.	J. bufonius
3	Plants perennial, often rhizomatous; inflorescence proportionately much smaller.	Lead 4
4	Leaves, except the involucres, all basal or nearly so, arising from well within the lower 1/4 of the stem.	Lead 5
4	Leaves cauline as well as basal, some arising from near or within the upper 1/2 of the stem.	Lead 8
5	Leaf blades terete, narrowly channeled on the upper side; capsule exceeding the perianth; seeds ca. 1 mm long, with a membranous appendage at each end.	J. vaseyi
5	Leaf blades flat or involute; capsule shorter than the perianth; seeds 0.3-0.5 mm long, merely minutely apiculate at each end.	Lead 6
6	Auricles flaplike, prolonged 1-5 mm beyond the summit of the sheath.	J. tenuis
6	Auricles not flaplike, low and rounded, only to 0.5 mm long.	Lead 7
7	Auricles cartilaginous, drying yellowish; bracteoles obtuse to subacute; leaf sheaths green, usually not reddish.	J. dudleyi
7	Auricles membranous, white or spotted with red or brown; bracteoles acute to acuminate or aristate; lower leaf sheaths often reddish.	J. interior
8	Capsule equaling or barely surpassing the outer tepals; stamens nearly reaching the summit of the perianth.	J. gerardii
8	Capsule much surpassing the outer tepals; stamens reaching the middle of the perianth.	J. compressus
9	Leaf blades flat, not hollow, not nodulose-septate or with only incomplete septae.	Lead 10
9	Leaf blades terete, hollow, nodulose-septate, the septae complete.	Lead 12
10	Leaves equitant, incompletely cross-septate; plants of moderate to high elevations in the Black Hills and westward.	J. ensifolius
10	Leaves not equitant, not at all cross-septate; plants more widespread in our range.	Lead 11
11	Tepals (4)5-6 mm long; stamens 6.	J. longistylis
11	Tepals 2-3.5 mm long; stamens 3.	J. marginatus
12	Glomerules obpyramidal to hemispheric, few- to 12-flowered, the flowers projecting upward.	Lead 13
12	Glomerules spherical, densely many-flowered, the flowers projecting outward in all directions at maturity.	Lead 16
13	Seeds 0.9-1.8 mm long, with membranous appendages at both ends; stamens 3.	Lead 14
13	Seeds 0.5 mm or less long, merely pointed at both ends; stamens 6.	Lead 15
14	Seeds 0.9-1.2 mm long, the body of the seed comprising 3/5 or more of its total length.	J. brevicaudatus
14	Seeds 1.2-1.9 mm long, the body of the seed comprising 1/2 or less of its total length.	J. canadensis
15	Inner tepals shorter than the outer ones, blunt to rounded; capsule rounded at the apex; inflorescence narrow, the branches mostly sharply ascending.	J. alpinus
15	Inner tepals longer than or about equaling the outer ones, acute to acuminate; capsule acute at the apex; inflorescence open, the branches spreading.	J. articulatus
16	Stamens 3, opposite the outer tepals.	Lead 17
16	Stamens 6, opposite both the inner and outer tepals.	Lead 18
17	Seeds with white, membranous, taillike appendages at both ends; capsule abruptly tapered to an apiculate tip.	J. canadensis
17	Seeds apiculate at both ends, without appendages; capsule gradually tapered to a slender beak ca. 1 mm long.	J. scirpoides
18	Inner and outer tepals equal in length, or nearly so; auricles membranous, yellowish.	J. nodosus
18	Outer tepals distinctly longer than the inner tepals; auricles white-hyaline.	J. torreyi