Flora of North America species comparison

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Juncus debilis

Juncus subg. Septati

weak rush
Habit Herbs, perennial, cespitose, 1–2.5 dm. Herbs, perennial (rarely annual), rhizomatous.
Culms

erect, terete, 1–2 mm diam., smooth.

terete.
Cataphylls

0–1, maroon or dark green, apex acute.

Leaves

basal 0–1, cauline 1–3;

auricles 1–1.5 mm, apex rounded, scarious;

blade maroon or dark green, terete, 1–12.5 cm × 0.5–1.5 mm.

basal and cauline: blade terete, nearly terete, or flattened, perfectly septate.
Inflorescences

terminal panicles of 3–50 heads, 2–8 cm, branches ascending to spreading;

primary bract erect;

heads 2–10-flowered, obpyramidal, 2–5 mm diam.

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

tepals green to straw-colored, lanceolate, 1.8–2.3(–2.5) mm, apex sharply acuminate;

stamens 3, 1/2 filament length.

in multiflowered heads (rarely only 2– or 3 flowers per head).
Capsules

exserted, straw-colored, 1-locular, narrowly ellipsoid to lanceoloid, 2.8–3.7 7(–4.2) mm, apex acute, valves separating at dehiscence.

1- or 3-locular, beaked.
Seeds

ellipsoid, 0.3–0.4 mm, not tailed;

body clear yellow-brown.

tailed or not tailed.
x

= 20.

Juncus debilis

Juncus subg. Septati
Phenology Fruiting summer.
Habitat Marshy shores, in small streams, swamps, wet clearings, spring runs, commonly in very soft mucky substrates
Elevation 0–700 m (0–2300 ft)
Distribution
from FNA
AL; AR; DE; FL; GA; IL; KY; LA; MD; MO; MS; NC; NJ; NY; PA; SC; TN; TX; VA; Mexicos (Chiapas); Central America (Honduras)
[WildflowerSearch map]
[BONAP county map]
Worldwide
Discussion

Juncus debilis A. Gray is a name being proposed for conservation.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Species ca. 80 (32 in the flora).

(Discussion copyrighted by Flora of North America; reprinted with permission.)
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
J. caesariensis
3. Stems and leaves smooth; auricles 0.2–0.4 mm
J. trigonocarpus
4. Seeds 1.1–1.9 mm; heads 5–50-flowered; inflorescence branches erect to ascending
J. 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
J. brachycephalus
5. Outer tepals acuminate to acute.
→ 6
6. Proximal inflorescence branches widely spreading
J. subcaudatus
6. Proximal inflorescence branches erect
J. 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
J. pelocarpus
8. Culms decumbent, 0.1–1 dm, forming mats
J. 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
J. acuminatus
11. Plants rhizomatous; tepals lance-subulate.
→ 12
12. Capsules included
J. 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.
J. 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
J. scirpoides
15. Heads spheric; stramineous to reddish brown, inner tepals shorter than outer; uppermost cauline leaf blade much shorter than its sheath
J. megacephalus
16. Tepals 4–5 mm; leaves laterally compressed
J. validus var. validus
16. Tepals 2.9–4 mm; leaves terete.
→ 17
17. Capsules 3.5–5 mm, exserted; culms 0.4–3 dm
J. nodosus
17. Capsules 3–3.5 mm; equaling perianth or slightly shorter; culms 2.5–8.5 dm
J. 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
J. pervetus
19. Heads 1–2.
→ 20
20. Tepals dark purplish brown to black; anthers 1/4 to equal filament length
J. mertensianus
20. Tepals light green, or light pink to white; anthers 2–3 times length of filaments
J. chlorocephalus
21. Outer tepals 2.4–4.1 mm, equaling inner tepals; auricles 0.5–1.7 mm
J. 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
J. torreyi
22. Outer tepals shorter than inner; capsules 5.2–6.5 mm
J. 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
J. bulbosus
25. Capsule acute to acuminate at apex, 3.5–6.1 mm; tepals 2.8–5.5 mm, acute to acuminate-subulate
J. 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
J. supiniformis
27. Capsules not beaked; plants erect.
→ 28
28. Capsule 1/3 longer than perianth, 2.8–4.2 mm
J. debilis
28. Capsule twice as long as perianth, 4–5.2 mm
J. diffusissimus
29. Heads 5–50; tepals 2.6–3.5 mm, nearly equal; capsules 2.8–3.5 mm
J. 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
J. nodatus
30. Leaf blade with faint ringlike bands at position of septa; roots often with terminal tubers; inner tepals 2.4–2.8 mm
J. 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
J. 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
J. articulatus
33. Capsules as long as tepals or exserted to 0.5 mm beyond tepals, apex obtuse below apex; outer tepals acute to obtuse
J. bulbosus
34. Proximal culm leaf overtopping inflorescences, distal culm leaf usually inflated, bladeless sheath; often developing filiform (hairlike) leaves off rhizome in running water
J. 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
J. alpinoarticulatus
36. Inner tepals acuminate; inflorescence spreading
J. articulatus
37. Capsule abruptly contracted at apex, usually not exserted
J. nevadensis
37. Capsule narrowed to beak, exserted at least slightly.
→ 38
38. Heads 2–9; tepals 2.8–5.5 mm
J. supiniformis
38. Heads 25–66; tepals 2.5–3.5 mm.
→ 39
39. Tepals nearly equal; heads with 6–10 flowers
J. dubius
39. Tepals unequal, outer shorter than inner; heads with 5–8 flowers
J. acutiflorus
Source FNA vol. 22. FNA vol. 22.
Parent taxa Juncaceae > Juncus > subg. Septati Juncaceae > Juncus
Sibling taxa
J. acuminatus, J. acutiflorus, J. acutus, J. alpinoarticulatus, J. anthelatus, J. arcticus, J. articulatus, J. biglumis, J. bolanderi, J. brachycarpus, J. brachycephalus, J. brachyphyllus, J. brevicaudatus, J. bryoides, J. bufonius, J. bulbosus, J. caesariensis, J. canadensis, J. capillaris, J. capitatus, J. castaneus, J. chlorocephalus, J. compressus, J. confusus, J. cooperi, J. coriaceus, J. covillei, J. dichotomus, J. diffusissimus, J. drummondii, J. dubius, J. dudleyi, J. effusus, J. elliottii, J. ensifolius, J. falcatus, J. filiformis, J. filipendulus, J. georgianus, J. gerardii, J. greenei, J. gymnocarpus, J. hallii, J. hemiendytus, J. howellii, J. inflexus, J. interior, J. kelloggii, J. leiospermus, J. lesueurii, J. longistylis, J. luciensis, J. macrandrus, J. macrophyllus, J. marginatus, J. maritimus, J. megacephalus, J. mertensianus, J. militaris, J. nevadensis, J. nodatus, J. nodosus, J. occidentalis, J. orthophyllus, J. oxymeris, J. parryi, J. patens, J. pelocarpus, J. pervetus, J. phaeocephalus, J. polycephalus, J. regelii, J. repens, J. roemerianus, J. scirpoides, J. secundus, J. squarrosus, J. stygius, J. subcaudatus, J. subtilis, J. supiniformis, J. tenuis, J. texanus, J. textilis, J. tiehmii, J. torreyi, J. trifidus, J. triformis, J. triglumis, J. trigonocarpus, J. uncialis, J. validus, J. vaseyi, J. xiphioides
Subordinate taxa
J. acuminatus, J. acutiflorus, J. alpinoarticulatus, J. articulatus, J. bolanderi, J. brachycarpus, J. brachycephalus, J. brevicaudatus, J. bulbosus, J. caesariensis, J. canadensis, J. chlorocephalus, J. debilis, J. diffusissimus, J. dubius, J. elliottii, J. megacephalus, J. mertensianus, J. militaris, J. nevadensis, J. nodatus, J. nodosus, J. pelocarpus, J. pervetus, J. scirpoides, J. subcaudatus, J. subtilis, J. supiniformis, J. texanus, J. torreyi, J. trigonocarpus, J. validus var. fascinatus, J. validus var. validus
Synonyms J. acuminatus var. debilis, J. radicans J. section Septati
Name authority A. Gray: Manual 481506. (1848) Buchenau: Abhandlungen herausgegeben vom naturwissenschaftlichen Vereine zu Bremen 4: 406. (1875)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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