Juncus mertensianus Bong.
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Family: Juncaceae
Genus: Juncus
Species Synonyms: Juncus slwookoorum S.B. Young
Common Names: slender-stemmed rush
Merten’s rush
Canada: Yukon Territory – British Columbia – western Alberta – southwestern Saskatchewan
Saskatchewan: southwestern Saskatchewan; Cypress Hills
Ecoregion: Cypress Upland
Saskatchewan: wet meadows
Provincial Status According
to Harms (2003):
Nature Conservancy Status:
Saskatchewan Species at
Risk Status:
Juncus mertensianus is threatened in Saskatchewan because it is rare or uncommon and is limited to the Cypress Hills.
Height: 5 – 40 cm
Roots: rhizomatous, sometimes very short (if plant caespitose), not swollen, branched
Stems: perennial, loosely to densely tufted, erect, terete, smooth
Leaves: basal leaves 1 – 2, cauline leaves 0 – 1, blade 0.5 – 1.5 cm long, green, flat; basal sheaths brown or purplish; auricles 1 mm long, apex rounded to acute, membranous or scarious
Inflorescence: head terminal, solitary or some with a second and smaller pedunculate head; heads 12 – 60-flowered, spherical; primary bract erect
Flowers: bracteoles absent; tepals all about the same length, inner may be slightly shorter than the outer, lanceolate to ovate, apex acute dark purplish-brown to black, shiny; stamens 6, anthers much shorter than filaments; stigmas 3
Fruits: capsules 2 – 3.5 mm long, included or slightly exserted, obovoid, chestnut brown, valves separating at dehiscence; seeds ellipsoid, not tailed, body yellowish-brown
1 Inflorescence appearing lateral; leaves all basal
1 Inflorescence appearing terminal; may have at least one blade-bearing leaf on lower stem or leaves all basal
2 Bract stout, much shorter than stem; perianth parts usually darker brown; anthers commonly much longer than their filaments
J. balticus
2 Bract slender, as long as or longer than stem; perianth parts greenish to light brown; anthers commonly shorter than or equal to their filaments
J. filiformis
3 Leaves nodulose-septate (divided by cross-partitions), terete, or if flattened, strongly equitant
3 Leaves not nodulose-septate, terete or if flattened, not equitant
4 Leaves strongly flattened and equitant
4 Leaves terete or slightly compressed
5 Styles surpassing petals; seeds with a distinct tail-like appendage
J. tracyi
5 Styles equal to petals; seeds without a tail
6 Stamens 3; auricles lacking
J. ensifolius
6 Stamens 6; auricles present
J. saximontanus
7 Flowers in dense spherical heads
7 Flowers few to many in narrower heads
8 Heads solitary; rhizomes densely matted
J. mertensianus
8 Heads solitary; rhizomes elongate and creeping, often bearing tubers
9 Tepals reddish-brown, inner tepals longer than or equal to outer tepals; leaves 1 – 2 mm thick; sheaths with yellowish auricles
J. nodosus var. nodosus
9 Tepals greenish to dull brown, inner tepals shorter than outer tepals; leaves to 5 mm thick; sheaths with hyaline auricles
J. torreyi
10 Seeds about 1 mm long, with definite white tail-like appendages
J. brevicaudatus
10 Seeds less than 0.5 mm long, apiculate but without white tails
11 Anthers shorter than or equalling their filaments; perianth segments obtuse; capsule exceeding the perianth
J. alpinoarticulatus ssp. nodulosus
11 Anthers distinctly longer than their filaments; perianth segments acute; capsule shorter than or equal to the perianth
J. nevadensis
12 Each flower inserted singly on the branches of the inflorescences and subtended by a pair of small bractlets in addition to the bractlet at the base of the pedicel
12 Each flower subtended only by the single bractlet at the base of the very short pedicel
13 Roots fibrous; dwarf species, branched near base; annuals; leaf sheaths not auricled
J. bufonius
13 Rhizomes elongate or short if culms densely tufted; plants not dwarfed or branched near the base; perennials; leaf sheaths auricled or prolonged
14 Leaf sheaths extending to about halfway up the culm
J. compressus
14 Leaf sheaths confined to base or only extending to about one third of the way up the stem
15 Sepals erect, closely appressed to the capsule
J. vaseyi
15 Sepals spreading to ascending, not closely appressed to the capsule
16 Auricles short and round; leaf blades less than half the length of the culm
J. dudleyi
16 Auricles delicate and scarious; leaf blades usually greater than half the length of the culm
17 Capsule 3-loculed, nearly equalling the perianth; inflorescence compact
J. confusus
17 Capsule 1-loculed, distinctly shorter than the perianth; inflorescence a loose panicle
18 Auricles prolonged into a membranous projection 3 – 5 mm long
J. tenuis
18 Auricles shorter, up to 2 mm long, submembranous
J. interior
19 Seeds apiculate; leaves flattened and grass-like
J. longistylus
19 Seeds with distinct white tail-like appendages; leaves terete to somewhat compressed or deeply channelled
20 Culms arising from elongate rhizomes; perianth and capsules dark brown to black
J. castaneus ssp. castaneus
20 Culms not rhizomatous, may form tussocks; perianth and capsules pale
21 Capsules to 9 mm long; heads 1 – 2; lower cauline leaves 1 – 3
J. stygius ssp. americanus
21 Capsules to 4 mm long; heads solitary; leaves all basal
J. albescens