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-locular or 3-locular, beaked. Seeds tailed or not tailed. x = 20.

Distribution

Worldwide

Discussion

Species ca. 80 (32 in the flora).

Selected References

None.

Lower Taxa

Juncus acuminatus, Juncus acutiflorus, Juncus alpinoarticulatus, Juncus articulatus, Juncus bolanderi, Juncus brachycarpus, Juncus brachycephalus, Juncus brevicaudatus, Juncus bulbosus, Juncus caesariensis, Juncus canadensis, Juncus chlorocephalus, Juncus debilis, Juncus diffusissimus, Juncus dubius, Juncus elliottii, Juncus megacephalus, Juncus mertensianus, Juncus militaris, Juncus nevadensis, Juncus nodatus, Juncus nodosus, Juncus pelocarpus, Juncus pervetus, Juncus scirpoides, Juncus subcaudatus, Juncus subtilis, Juncus supiniformis, Juncus texanus, Juncus torreyi, Juncus trigonocarpus, Juncus validus

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