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Juncus tenuis

Higher Taxonomy
Family: JuncaceaeView DescriptionDichotomous Key

Common Name: RUSH FAMILY
Habit: Annual, perennial herb generally from rhizomes. Stem: round or flat. Leaf: generally basal; sheath margins fused, or overlapping and generally with 2 ear-like extensions at blade junction; blade round, flat, or vestigial, glabrous or margin hairy. Inflorescence: head-like clusters or flowers 1, variously arranged; bracts subtending inflorescence 2, generally leaf-like; bracts subtending inflorescence branches 1--2, reduced; bractlets subtending flowers generally 1--2, generally translucent. Flower: generally bisexual, radial; sepals and petals similar, persistent, scale-like, green to brown or +- purple-black; stamens generally 3 or 6, anthers linear, persistent; pistil 1, ovary superior, chambers generally 1 or 3, placentas 1 and basal or 3 and axile or parietal, stigmas generally > style. Fruit: capsule, loculicidal. Seed: 3--many, generally with white appendages on 1 or both ends.
Genera In Family: 7 genera, 440 species: temperate, arctic, and tropical mountains. Note: Flowers late spring to early fall.
eFlora Treatment Author: Peter F. Zika, except as noted
Scientific Editor: Douglas H. Goldman, Bruce G. Baldwin.
Genus: JuncusView DescriptionDichotomous Key

Common Name: RUSH
Habit: Rhizome 0 or generally with scale-like leaves. Stem: generally cylindric or flat. Leaf: blade well developed and cylindric or flat, occasionally closely resembling stem, or reduced to small point; crosswalls generally present; appendages generally present at blade-sheath junction. Inflorescence: generally terminal, appearing lateral when pushed aside by inflorescence bract; bractlets 0--2. Flower: sepals, petals similar; stamens generally 3 or 6(2); pistil 1, ovary chambers 1--3, placentas axile or parietal, stigmas generally 3(2). Seed: many.
Species In Genus: 315 species: worldwide, especially northern hemisphere. Etymology: (Latin: to join or bind, from use of stems) Note: All species with leaf crosswalls may have leaves, stems swollen, deformed by sucking insects. Fruiting time given instead of flowering time. Plants included in TJM2 as Juncus brachyphyllus now treated in California as a new species, Juncus trilocularis (Zika 2012 Rhodora 114:309--329); Juncus bulbosus, Juncus dichotomus, and Juncus elliottii, only noted as naturalized in TJM2, now fully treated.

Juncus tenuis Willd.
Habit: Perennial herb, cespitose, stem 20--60 cm, generally 0--1 strong ridges per side. Leaf: sheath margins membranous, sheath appendages generally acute to acuminate, thin, +- translucent, generally 1--8 mm until late in season when generally smaller or 0; blade with flat side toward stem, 1/2 to = stem, 1--1.3 mm wide, not stiff, crosswalls 0. Inflorescence: +- open; lower bracts leaf-like, generally > inflorescence; branches unequal; flowers 1, generally > internodes, +- denser near branch tips; bractlets 2 per flower, acute to blunt. Flower: perianth parts 3--4.5 mm, +- equal, lanceolate, acuminate, spreading in fruit, green to +- red or pale brown; stamens 6, filaments >> anthers. Fruit: < perianth, widely ovoid, blunt to acute; chamber 1, partitions incomplete. Seed: 0.4--0.5 mm, oblong; appendages minute, blunt. Chromosomes: 2n=80.
Ecology: Uncommon. Damp places; Elevation: generally < 1500 m. Bioregional Distribution: NW, CaR, SN (exc Teh), GV, CCo, SnGb, MP; Distribution Outside California: North America, introduced worldwide except Antarctica. Fruiting Time: Jun--Sep Note: Hybridizes with Juncus occidentalis.
eFlora Treatment Author: Peter F. Zika
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botanical illustration including Juncus tenuis


Citation for this treatment: Peter F. Zika 2016. Juncus tenuis, in Jepson Flora Project (eds.) Jepson eFlora,, accessed on May 31, 2016.

Citation for the whole project: Jepson Flora Project (eds.) 2016. Jepson eFlora,, accessed on May 31, 2016.

Juncus tenuis
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© 2005 Steve Matson
Juncus tenuis
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© 2003 Steve Matson
Juncus tenuis
click for enlargement
© 2008 Keir Morse
Juncus tenuis
click for enlargement
© 2005 Steve Matson
Juncus tenuis
click for enlargement
© 2005 Steve Matson
Juncus tenuis
click for enlargement
© 2008 Keir Morse

More photos of Juncus tenuis in CalPhotos

Geographic subdivisions for Juncus tenuis:
NW, CaR, SN (exc Teh), GV, CCo, SnGb, MP;
Markers link to CCH specimen records. Yellow markers indicate records that may provide evidence for eFlora range revision or may have georeferencing or identification issues. Purple markers indicate specimens collected from a garden, greenhouse, or other non-wild location.
map of distribution 1
(Note: any qualifiers in the taxon distribution description, such as 'northern', 'southern', 'adjacent' etc., are not reflected in the map above, and in some cases indication of a taxon in a subdivision is based on a single collection or author-verified occurence).

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Data provided by the participants of the Consortium of California Herbaria.
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CCH collections by month

Duplicates counted once; synonyms included.
Species do not include records of infraspecific taxa.
Blue line denotes eFlora flowering time.