Herbs, perennial (rarely annual), rhizomatous. Culms terete. Leaves basal and cauline: blade terete, nearly terete, or flattened, perfectly septate. Inflorescences terminal panicles or racemes of 2 to –many heads, a single terminal head, or rarely a cyme of heads, sympodial; bracts erect or ascending, flat, involute or terete; bracteoles absent. Flowers in multiflowered heads (rarely only 2– or 3 flowers per head). Capsules 1- or 3-locular, beaked. Seeds tailed or not tailed. x = 20.

Discussion

Species ca. 80 (32 in the flora).

Selected References

None.

Key

1 Seeds tailed, 0.7–2.6 mm, including tails; seed body covered with whitish translucent veil. > 2
1 Seeds not tailed, 0.3–0.7 mm; seed body clear yellow-brown. > 7
2 Seeds 1.8–2.6 mm, including tails; stamens usually 6. > 3
2 Seeds 0.7–1.9 mm, including tails; stamens usually 3. > 4
3 Stems and leaves scabrous; auricles 1–7.5 mm Juncus caesariensis
3 Stems and leaves smooth; auricles 0.2–0.4 mm Juncus trigonocarpus
4 Seeds 1.1–1.9 mm; heads 5–50-flowered; inflorescence branches erect to ascending Juncus canadensis
4 Seeds 0.7–1.2 mm; heads 2–8-flowered or if to 20-flowered then proximal inflorescence branches widely spreading (J. subcaudatus). > 5
5 Outer tepals obtuse to nearly acute Juncus brachycephalus
5 Outer tepals acuminate to acute. > 6
6 Proximal inflorescence branches widely spreading Juncus subcaudatus
6 Proximal inflorescence branches erect Juncus brevicaudatus
7 Flowers 1–2(–4) at each node, not in heads; capsules fertile only below middle. > 8
7 Flowers in heads of 3–60; capsules fertile throughout or only below middle. > 9
8 Culms erect, 0.3–7 dm, not forming mats Juncus pelocarpus
8 Culms decumbent, 0.1–1 dm, forming mats Juncus subtilis
9 Heads spheric or nearly spheric, 15–60-flowered > 10
9 Heads obconic to hemispheric, 3–15-flowered. > 23
10 Stamens 6. > 18
10 Stamens 3. > 11
11 Plants cespitose; tepals lanceolate Juncus acuminatus
11 Plants rhizomatous; tepals lance-subulate. > 12
12 Capsules included Juncus brachycarpus
12 Capsule exserted to slightly included. > 13
13 Capsules remaining united at apex after dehiscence. > 14
13 Capsule valves separating at apex during dehiscence. > 16
14 Leaves laterally compressed, 3–5 mm diam. Juncus validus var. fascinatus
14 Leaves terete, 1–4 mm diam. > 15
15 Heads sometimes spheric, usually lobed; tepals green to stramineous, nearly equal; uppermost cauline leaf blade (below inflorescence bract) equaling or longer than its sheath Juncus scirpoides
15 Heads spheric; stramineous to reddish brown, inner tepals shorter than outer; uppermost cauline leaf blade much shorter than its sheath Juncus megacephalus
16 Tepals 4–5 mm; leaves laterally compressed Juncus validus var. validus
16 Tepals 2.9–4 mm; leaves terete. > 17
17 Capsules 3.5–5 mm, exserted; culms 0.4–3 dm Juncus nodosus
17 Capsules 3–3.5 mm; equaling perianth or slightly shorter; culms 2.5–8.5 dm Juncus bolanderi
18 Tepals lanceolate to lance-ovate, light green to light pink or white or dark purplish brown; capsule ovoid to obovoid, 1.9–3.5 mm; heads 1–2 per inflorescence (15–50 for J. pervetus). > 19
18 Tepals lance-subulate, green to stramineous; capsule lance-subulate, 3.2–6.5 mm; heads 1–23 per inflorescence. > 21
19 Heads 15–50 Juncus pervetus
19 Heads 1–2. > 20
20 Tepals dark purplish brown to black; anthers 1/4 to equal filament length Juncus mertensianus
20 Tepals light green, or light pink to white; anthers 2–3 times length of filaments Juncus chlorocephalus
21 Outer tepals 2.4–4.1 mm, equaling inner tepals; auricles 0.5–1.7 mm Juncus nodosus
21 Outer tepals 4–6 mm, outer and inner tepals unequal in length; auricles 1–4 mm. > 22
22 Outer tepals longer than inner; capsule 4.3–5.7 mm Juncus torreyi
22 Outer tepals shorter than inner; capsules 5.2–6.5 mm Juncus texanus
23 Stamens 3. > 24
23 Stamens 6. > 31
24 Stems creeping or floating, capillary; filiform, submersed leaves often formed before flowering; inflorescences with 1–9 heads. > 25
24 Stems erect, not floating; filiform leaves absent; inflorescences with 3–200 heads. > 26
25 Capsule rounded at apex, 2.5–4 mm; tepals 2–3.6 mm, obtuse to acute Juncus bulbosus
25 Capsule acute to acuminate at apex, 3.5–6.1 mm; tepals 2.8–5.5 mm, acute to acuminate-subulate Juncus supiniformis
26 Capsule much longer than perianth, 1.3–2 times perianth length. > 27
26 Capsule equaling or just exceeding perianth. > 29
27 Capsules beaked; plants often decumbent or matted Juncus supiniformis
27 Capsules not beaked; plants erect. > 28
28 Capsule 1/3 longer than perianth, 2.8–4.2 mm Juncus debilis
28 Capsule twice as long as perianth, 4–5.2 mm Juncus diffusissimus
29 Heads 5–50; tepals 2.6–3.5 mm, nearly equal; capsules 2.8–3.5 mm Juncus acuminatus
29 Heads 30–250; tepals 1.7–2.9 mm, inner tepals shorter than outer tepals; capsules 1.9–2.9 mm. > 30
30 Leaf blade with prominent and conspicuous ringlike bands at position of cross partitions; roots without terminal tubers; inner tepals 1.7–2.1 mm Juncus nodatus
30 Leaf blade with faint ringlike bands at position of septa; roots often with terminal tubers; inner tepals 2.4–2.8 mm Juncus elliottii
31 Stems creeping or floating, capillary; filiform, submersed leaves often formed before flowering; inflorescences with 1–9 heads. > 32
31 Stems erect; filiform submersed leaves not formed except in J. militaris; heads 1–66. > 34
32 Auricles 0.8–2.1 mm; capsules 3.5–6.1 mm Juncus supiniformis
32 Auricles 0.4–1 mm; capsules 2.5–4 mm. > 33
33 Capsules exserted about 1 mm beyond perianth; apex acute below beak; outer tepals acute to acuminate Juncus articulatus
33 Capsules as long as tepals or exserted to 0.5 mm beyond tepals, apex obtuse below apex; outer tepals acute to obtuse Juncus bulbosus
34 Proximal culm leaf overtopping inflorescences, distal culm leaf usually inflated, bladeless sheath; often developing filiform (hairlike) leaves off rhizome in running water Juncus militaris
34 Proximal culm leaf shorter than inflorescence, distal culm leaf usually with blade, sheath not inflated; not developing filiform leaves off rhizome. > 35
35 Tepals 1.6–3 mm; apex obtuse to acuminate, usually not subulate mucronate; anthers shorter than to equaling filaments. > 36
35 Tepals 2.3–6.2 mm; apex usually acuminate with subulate mucro (acute in J. acutiflorus); anthers equaling or longer than filaments. > 37
36 Inner tepals obtuse; inflorescence stiffly erect Juncus alpinoarticulatus
36 Inner tepals acuminate; inflorescence spreading Juncus articulatus
37 Capsule abruptly contracted at apex, usually not exserted Juncus nevadensis
37 Capsule narrowed to beak, exserted at least slightly. > 38
38 Heads 2–9; tepals 2.8–5.5 mm Juncus supiniformis
38 Heads 25–66; tepals 2.5–3.5 mm. > 39
39 Tepals nearly equal; heads with 6–10 flowers Juncus dubius
39 Tepals unequal, outer shorter than inner; heads with 5–8 flowers Juncus acutiflorus