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Published In: Species Plantarum 1: 325. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library
 

Project Name Data (Last Modified On 7/9/2009)
Acceptance : Accepted
Project Data     (Last Modified On 7/22/2009)

 

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1. Juncus L. (rush)

Plants sometimes with rhizomes and/or tubers, the aboveground growth caespitose or spaced along the rhizome. Aerial stems usually erect or ascending, usually unbranched below the inflorescence. Leaves glabrous, the leaf blades flat, tubular, or folded longitudinally with boat-shaped tips, the basal leaves usually few, sometimes reduced to bladeless sheaths, the leaves of the aerial stems absent or few, the sheaths open. Inflorescences panicles or sometimes reduced to racemes, usually with 1 or more leaflike or stemlike bracts at the base, the individual flowers single, in small clusters, or in dense, headlike clusters. Flowers in some species subtended by 2 small, triangular to ovate bracts, in addition to the single bracts scattered through the inflorescence. Sepals and petals similar to one another or sometimes the sepals slightly longer, lanceolate to ovate, erect or with the acute to attenuate (rarely obtuse) tips somewhat spreading, green or straw-colored to brown, usually firm-textured with scarious margins. Stamens 3 or 6. Fruits shorter than or longer than the perianth, obovoid to linear-attenuate, straw-colored to brown (sometimes black or nearly so in J. gerardii). Seeds usually numerous, 0.3–2.0 mm long, ellipsoid to ovoid, yellow or brown, lacking a caruncle (caplike appendage), but in some species with one or both ends tapered into short or long, tail-like appendages, the surfaces variously pitted or honeycombed. About 225 species, worldwide, but most diverse from temperate regions to the Arctic.

The species of Juncus can be difficult to determine. Keying sterile or flowering specimens is sometimes impossible, because in most species the mature capsules provide characters critical to species determination. To correctly identify a specimen, it is important to observe whether the individual flowers are closely subtended by a pair of short bracts, as opposed to the scattered small bracts in the inflorescences of other species groups.

The rushes are important components of many prairie and wetland communities. Most of the species are good for erosion control in some situations, and several species are effective colonizers of disturbed habitats. The seeds and rootstocks provide food for diverse wildlife species, and the aboveground portions are good forage for livestock and native grazing mammals.

Individuals of some species, particularly J. torreyi, produce aberrant inflorescences in which most of the flowers in each cluster are replaced by longer, green, leaflike structures. These gall-like growths are produced in response to parasitism by small insects, particularly members of the Homopteran genus of jumping plant lice, Livia Latreille.

 

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1 Inflorescence appearing to originate from the side of the stem, which continues vertically as a tubular, stemlike bract (2)
+ Inflorescence appearing terminal (3)
2 (1) Aerial stems caespitose along short, branched rhizomes, with 30–60 fine, longitudinal lines or ribs (most easily seen when dry); stamens 3 12 Juncus effusus
+ Aerial stems spaced along the widely creeping rhizome, often appearing aboveground in a line, lacking ribs (sometimes with short, faint, longitudinal lines when dry); stamens 6 3 Juncus balticus
3 (1) Leaf blades variously shaped, but lacking regularly spaced cross-partitions (4)
+ Leaf blades tubular and hollow (often drying flat), with cross-partitions at regular intervals visible as darker or raised lines or harder places (12)
4 (3) Individual flowers not subtended by 2 bracts, but bracts occurring singly scattered through the inflorescence; flowers mostly in few- to many-flowered clusters (5)
+ Individual flowers subtended by 2 small, triangular to ovate bracts in addition to the single bracts occurring scattered through the inflorescence; flowers mostly produced singly along the inflorescence branches (6)
5 (4) Aerial stems robust, 3–5 mm in diameter at the base, 60–130 cm tall, the rhizomes stout and conspicuous; blades of main leaves 4–7 mm wide; flowers in clusters of 2–5, 20–150 clusters per inflorescence 4 Juncus biflorus
+ Aerial stems slender, 1–3 mm in diameter at the base, 15–60(–80) cm tall, the rhizomes slender and inconspicuous; blades of main leaves 1–4 mm wide; flowers in clusters of 5–20, 2–20 clusters per inflorescence 15 Juncus marginatus
6 (4) Inflorescence 1/3–3/4 of the total plant height; plants annual, with soft bases 7 Juncus bufonius
+ Inflorescence usually less than 1/4 of the total plant height; plants perennial, with firm hard bases, often with rhizomes and/or tubers (7)
7 (6) Leaves of the aerial stems usually 1–3 in the lower half (excluding the leaflike bracts at the base of the inflorescence); sepals and petals narrowed to blunt, incurved tips 13 Juncus gerardii
+ Leaves all basal or nearly so (excluding the leaflike bracts at the base of the inflorescence); sepals and petals acute to acuminate, erect or spreading (8)
8 (7) Auricles at the top of the leaf sheaths 1.0–3.5 mm long, appearing as loose, white, thin flaps of tissue protruding from the sheath apex 21 Juncus tenuis
+ Auricles at the top of the leaf sheaths less than 1 mm long, appearing short and rounded, not protruding from the sheath apex (9)
9 (8) Perianth 2.5–4.0 mm long; bract at the base of the inflorescence shorter than the inflorescence; leaves usually less than 1/3 the height of the aerial stems (including the inflorescence); flowers mostly along the inner side of the inflorescence branches, which tend to curve inward near the tip 19 Juncus secundus
+ Perianth 3.5–6.0 mm long; bract at the base of the inflorescence longer than the inflorescence; leaves usually about 1/2 the height of the aerial stems (including the inflorescence); flowers mostly crowded near the tips of the inflorescence branches or not apparently produced along the inner side of the inflorescence branches, which are straight or arching outward (10)
10 (9) Auricles light yellow, hard and rigid, cartilaginous 11 Juncus dudleyi
+ Auricles white to tan or grayish brown, papery, not hard or cartilaginous (11)
11 (10) The 2 small bracts subtending each flower rounded or narrowed to blunt tips; fruits with 3 locules 6 Juncus brachyphyllus
+ The 2 small bracts subtending each flower acuminate; fruits with 1 locule or sometimes with 3 incomplete cross-walls protruding about halfway to the middle of the fruit 14 Juncus interior
12 (3) Petals rounded or blunt at the tips, the sepals acutely pointed 2 Juncus alpinoarticulatus
+ Petals and sepals with the tips acutely pointed or acuminate (13)
13 (12) Sepals and petals about 1/2 as long as the mature fruits 10 Juncus diffusissimus
+ Sepals and petals 3/4 as long as to longer than the mature fruits (14)
14 (13) Mature fruits 1/2–3/4 as long as the sepals and petals 5 Juncus brachycarpus
+ Mature fruits longer than to slightly shorter than the sepals and petals (15)
15 (14) Seeds 0.7–2.0 mm long, with an acuminate, tail-like appendages at each end (16)
+ Seeds 0.3–0.5 mm long, lacking tail-like appendages, the ends rounded or with short, dark, pointed tips (17)
16 (15) Seeds 1.3–2.0 mm long, the tail-like appendages 2/3 to nearly as long as the body; branches of the inflorescence mostly stiffly ascending 8 Juncus canadensis
+ Seeds 0.7–1.3 mm long, the tail-like appendages about 1/3 as long as the body or less, 1 of the appendages usually shorter than the other; at least some of the branches of the inflorescence loosely spreading 20 Juncus subcaudatus
17 (15) Flowers in small clusters of 2–7(–10) (18)
+ Flowers mostly in headlike clusters of 10–100 (19)
18 (17) Mature fruits 2.1–2.8 mm long, rounded or short-acuminate at the tips, about as long as the perianth; flower clusters mostly 50–200 or more per inflorescence; largest leaves 3–5 mm wide 16 Juncus nodatus
+ Mature fruits 2.8–4.2 mm long, conspicuously longer than the perianth; flower clusters mostly 3–35 per inflorescence; leaves 0.5–1 mm wide 9 Juncus debilis
19 (17) Leaf blades somewhat flattened, elliptic to narrowly elliptic in cross-section 23 Juncus validus
+ Leaf blades not flattened, circular in cross-section or nearly so (20)
20 (19) Stamens 3 per flower (opposite the sepals) (21)
+ Stamens 6 per flower (opposite the sepals and petals; search for remaining filaments opposite the petals in older fruiting specimens) (22)
21 (20) Rhizomes and tubers absent; fruits narrowly ovate to elliptic in outline, the tip acute with a small mucro (hard tooth or point) 1 Juncus acuminatus
+ Stout, tuberous rhizomes present; fruits narrowly lanceolate in outline, tapering gradually to a long beak 18 Juncus scirpoides
22 (20) Plants mostly 10–40 cm tall; sepals mostly 2.5–3.5 mm long, slightly shorter than to about as long as the petals; auricles at the top of the leaf sheaths 0.5–1.0 mm long, hard and often light yellow 17 Juncus nodosus
+ Plants mostly 40–100 cm tall; sepals mostly 4–6 mm long, slightly longer than the petals; auricles at the top of the leaf sheaths 2–5 mm long, papery, white 22 Juncus torreyi
 
 
 
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