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Juncus
See list of 38 species in this genusReferences: Hämet-Ahti (1980), Brooks and Clemants (2000).
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1a. Involucral bract solitary, of similar cross-sectional shape as the stem and appearing to be a continuation of it, therefore, the inflorescence appearing to emerge from the side of the stem (i.e., pseudolateral) [Figs. 146,150]; leaves bladeless, consisting of sheaths only
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2a. Stems cespitose; flowers with 3 stamens (or with 6 stamens in the rare introduction J. inflexus)
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3a. Capsules red-brown to dark brown, (2.5–) 3–4 mm long; stamens numbering 6 per flower, with filaments 0.8–1.5 mm long and anthers 0.8–1 mm long; stems prominently glaucous in life
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3b. Capsules tan to green-tan or brown, 1.5–3.2 mm long; stamens numbering 3 per flower, with filaments 0.5–0.8 mm long and anthers 0.5–0.8 mm long; stems green
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4a. Apical portion of stem relatively lustrous, smooth or nearly so below the inflorescence, the (25–) 30–60 longitudinal striations inconspicuous until drying [Fig. 146]; ridges of dried stems capped with dull, low cells
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4b. Apical portion of stem relatively dull, evidently ridged below the inflorescence with mostly 10–30 longitudinal grooves [Fig. 150]; ridges of dried stems capped with lustrous, papillose cells
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5a. Involucral bract swollen at the base of the inflorescence, sometimes somewhat reflexed in fruit; leaf sheaths with red-brown bases, the upper ones 15–23 cm long; inflorescence compact, mostly 10–25 mm in diameter; stems with 12–30 longitudinal ridges; tepals spreading from the base in fruit
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5b. Involucral bract not swollen, erect in fruit; leaf sheaths with dark red-brown to purple-black bases, the upper ones 5–12 cm long; inflorescence relatively open, mostly 15–80 mm in diameter; stems with 10–20 longitudinal ridges [Fig. 150]; tepals ascending or appressed to the capsule in fruit
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2b. Stems produced singly or a few together from an elongate rhizome; flowers with 6 stamens
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6a. Anthers 3–5 times as long as the filaments; tepals usually with a dark stripe on each side of the midvein [Fig. 143]; stems smooth in life, irregularly wrinkled when dry
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6b. Anthers 0.3–0.5 times as long as the filaments; tepals lacking dark stripes; stems finely grooved
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1b. Involucral bracts usually 2 or more, differentiated from the stem in some manner, the inflorescence appearing terminal [Fig. 151]; leaves with blades
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7a. Flowers occurring singly on pedicels [Fig. 142]; leaves variously flat to terete, never septate; bracteoles present, these a pair of small bracts at the base of the flowers in addition to the pair of bracts at the base of the pedicels
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8a. Plants annual with fibrous roots; inflorescence often occupying 33–90% of the total plant height; leaves without auricles
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9a. Inner tepals acute to acuminate, exceeding the capsule [Fig. 144]; capsules mostly acute to subacute at apex (rarely truncate); inflorescences relatively open
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9b. Inner tepals rounded to acute at the apex, many equaling or shorter than the capsule [Fig. 141]; capsules mostly truncate at apex; inflorescences relatively dense
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8b. Plants perennial; inflorescences rarely occupying more than 25% of the total plant height; leaves with auricles
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10a. Auricles erose; inflorescence of 1–3 flowers; capsules with a beak up to 0.7 mm long; margins of leaf blades minutely serrulate
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10b. Auricles entire; inflorescence with several to many flowers; capsules usually beakless (rarely shortly beaked; e.g., J. gerardii); margins of leaf blades entire
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11a. Leaves terete or caniculate; tepals shorter than and appressed to the capsule; capsules 3-locular, the septa meeting in the middle
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12a. Seeds with inconspicuous pale tails at each end less than 0.2 mm long; capsules 2.9–3.5 (–4) mm long, brown to dark brown; inner tepals mostly 1.9–3.4 mm long
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12b. Seeds with conspicuous, slender, slightly curved pale tails at each end 0.2–0.4 mm long; capsules (3.3–) 3.8–4.7 mm long, golden brown to light brown; inner tepals mostly 3.2–4 mm long
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11b. Leaves flat or becoming involute (nearly terete in some J. dichotomus); tepals equal to or longer than the capsule (often shorter in J. compressus), ascending to spreading; capsules partially 3-locular, the septa not meeting in the center or 3-locular in J. gerardii and J. secundus
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13a. Leaves not confined to the base of the stem, some borne on the upper ½ of the stem; tepals with a dark-stripe on each side of the midvein, the outer with an obtuse apex; stems produced singly or a few together from elongate rhizomes (varying to subcespitose in J. compressus); plants of saline habitats
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14a. Anthers 1.1–1.6 (–1.8) mm long, 2–4 times as long as the filament; capsules usually shorter than to equaling the length of the tepals; primary bract of the inflorescence mostly 1–5 cm long, usually not conspicuously exceeding the inflorescence
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14b. Anthers 0.6–1 mm long, 1–2 times as long as the filament; capsules usually exceeding the tepals; primary bract of the inflorescence 2–7.5 (–13) cm long, often conspicuously exceeding the inflorescence
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13b. Leaves confined primarily to the lower ⅓ of the stem; tepals lacking dark stripes, the outer acuminate at the apex; stems cespitose; plants of non-saline habitats
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15a. Auricles scarious, (1–) 1.5–5 mm long; sheath margin pliable, transparent
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16a. Monochasial branches of inflorescence erect to divergent, with crowded to remote flowers, the internodes less than 6 mm long [Fig. 151]; ultimate branches of monochasia 1–2 cm long; tepals (2.8–) 3.5–4.5 mm long; capsules more than 75% of the length of the tepals [Fig. 151]; plants usually shorter than 7 dm
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16b. Monochasial branches of inflorescence erect to ascending, often with inwardly curving branches, with widely scattered flowers, the internodes 6 mm or longer [Fig. 142]; ultimate branches of monochasia mostly 3–5 cm long; tepals 2.5–3.5 (–4) mm long; capsules less than 75% of the length of the tepals [Fig. 142]; plants mostly 7–9 dm tall
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15b. Auricles scarious to cartilaginous, 0.2–0.6 mm long; sheath margin of firmer texture, often brittle, transparent to opaque
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17a. Capsule 3-locular; placentation axile; leaves relatively short, often not exceeding midpoint of stem
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17b. Capsules only partially 3-locular, the incomplete septa not meeting in the center; placentation parietal; leaves usually extending past midpoint of stem
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18a. Leaves caniculate to nearly terete, rarely flat; inflorescence varying from compact to open and diffuse, usually with 10–35 or more flowers
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18b. Leaves flat, though often involute in age or drying; inflorescence usually compact and few-flowered, often with 10 or fewer flowers, rarely more than 15
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7b. Flowers borne in glomerules (sometimes solitary in J. pelocarpus and J. subtilis); leaves both terete and septate (except in J. biflorus, J. ensifolius, J. marginatus, and J. stygius); bracteoles absent, flowers subtended by only a pair of bracts at the base of the pedicel
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19a. Leaf blades compressed and equitant (i.e., set edge to stem), imperfectly septate (i.e., the septa inconspicuous and not continuous through the blade width)
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19b. Leaf blades elliptic to terete in cross-section, septate (imperfectly septate in J. stygius) or flat and non-septate, never equitant
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20a. Capsules 5.5–7 (–9) mm long; seeds 2.8–3.5 mm long including the white tails; leaves terete to elliptic in cross-section, imperfectly septate
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20b. Capsules 1.5–5.2 mm long; seeds 0.3–1.9 mm long; leaves either flat or both terete and septate
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21a. Leaves flat, without septa; capsules subglobose, often with red flecks [Fig. 148]
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22a. Widest leaf blades (1.3–) 1.6–2.6 (–3.5) mm wide; anthers (0.2–) 0.3–0.5 (–0.7) mm long, concealed by the tepals; tallest stems (19.2–) 26–44 (–56.8) cm tall; sheath of lowest leaf (17–) 22–38 (–47) mm long; base of stem (0.4–) 2–4.4 (–6) mm thick; inflorescence with (2–) 5–15 (–30) glomerules
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22b. Widest leaf blades (2.6–) 3.1–4.5 (–5.4) mm wide; anthers (0.5–) 0.6–1 (–1.3) mm long, exserted beyond tepals; tallest stems (27.2–) 50.8–81.2 (–100.7) cm tall; sheath of lowest leaf (32–) 43–78 (–97) mm long; base of stem (3.4–) 5.8–9.6 (–12) mm thick; inflorescence with 20–100 (–200) glomerules
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21b. Leaves terete and septate; capsules mostly obloid to ellipsoid or ovoid, without red flecks
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23a. Seeds 0.7–1.9 mm long including the pale tails at each end [Fig. 145], the body of the seed covered with a translucent, pale white veil (note: view at 20 × magnification); flowers usually with 3 stamens
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24a. Seeds 1.1–1.9 mm long, each tail 50–80% as long as the seed body [Fig. 145]; glomerules 5- to 50-flowered
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24b. Seeds 0.7–1.2 mm long, each tail 10–40% as long as the seed body; glomerules 2- to 10-flowered, rarely with as many as 20 flowers in J. subcaudatus
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25a. Outer tepals obtuse to subacute at the apex, soft, with conspicuous scarious margins, 1.8–2.5 mm long; capsules 2.4–3.8 mm long
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25b. Outer tepals sharply acute to acuminate, rigid, with narrow scarious margins, 2.1–3.2 mm long; capsules 3–4.8 mm long
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26a. Branches of inflorescence erect to strictly ascending; capsules 3.2–4.8 mm long, prominently exserted, extending more than 0.7 mm beyond perianth; glomerules with 2–5 (–7) flowers
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26b. Branches of inflorescence widely ascending to spreading; capsules 3–3.8 mm long, weakly to prominently exserted, not exceeding tepals by more than 0.6 (–1.3) mm; glomerules with 2–10 (–20) flowers
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23b. Seeds 0.3–0.7 mm long, merely pointed at the ends, the body clear yellow-brown to red-brown; flowers with 3 or 6 stamens
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27a. Flowers solitary or paired, sometimes replaced by vegetative bulbils [Fig. 149]
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28a. Stems upright; inflorescences many-flowered; outer tepals 1.6–2.3 mm long
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28b. Stems creeping or floating; entire plant with only 1–3 flowers; outer tepals (1.8–) 2.2–2.8 mm long
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27b. Flowers in glomerules of 2–100, not replaced by bulbils
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29a. Leaves dimorphic—those produced by the rhizome submersed and capillary, those produced by the stem emergent and thicker; lowest stem leaf overtopping inflorescence, 3–6 mm thick at midpoint
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29b. Leaves monomorphic, none capillary and produced by the rhizome; lowest stem leaf shorter than height of plant, mostly 0.5–3 mm thick
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30a. Glomerules spheric or subspheric, comprised of (6–) 10–100 flowers
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31a. Inflorescences composed of 24–60 glomerules; inner tepals obtuse to subacute at the apex
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31b. Inflorescences composed of 1–23 glomerules; inner tepals acuminate at the apex
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32a. Plants cespitose, without elongate rhizomes; tepals lanceolate to narrow-ovate (in part)
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32b. Plants not cespitose, the stems produced singly or a few together from elongate rhizomes; tepals subulate
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33a. Flowers with usually 3 stamens; capsules included within the perianth, the tips of the valves separate after dehiscence
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33b. Flowers with usually 6 stamens; capsules equaling tepals to exserted, the tips of the valves often cohering after dehiscence
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34a. Auricles 0.5–1 (–1.7) mm long, cartilaginous, dark yellow; glomerules composed of 6–25 (–30) flowers; inner and outer tepals of ± similar length
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34b. Auricles (1–) 2–4 mm long, scarious, pale brown; glomerules composed of 25–100 flowers; inner tepals shorter than outer tepals
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30b. Glomerules hemispheric to obconic, comprised of 2–20 flowers
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35a. Flowers with usually 3 stamens; plants cespitose; capsules light brown, 1-locular
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36a. Capsule approximately equal in length to tepals; glomerules composed of 5–20 (or more) flowers (in part)
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36b. Capsule evidently exserted beyond tepals; glomerules composed of 2–10 flowers
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37a. Capsules 2.8–3.7 (–4.2) mm long, approximately 1.3–1.5 times as long as the tepals; outer tepals 1.8–2.3(–2.5) mm long
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37b. Capsules 4–5.2 mm long, approximately 2 times as long as the tepals; outer tepals (2–)2.6–3.2 mm long
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35b. Flowers with usually 6 stamens; plants not cespitose, produced singly or a few together from elongate rhizomes (sometimes subcespitose in J. articulatus); capsules brown to dark brown, imperfectly 3-locular (i.e., the septa not extending all the way to the center)
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38b. Capsules acute (seldom obtuse) at apex; inner tepals acute to acuminate at apex; branches of inflorescence widely ascending to spreading
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Each photo represents one species in this genus.