Juncus

Juncus
Habit of J. conglomeratus
Flower of J. squarrosus showing: 6 spreading tepals, anthers (upright yellow, held on white filaments), ovary (green) with stigma (pinkish tip column) and styles (white)
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Clade: Commelinids
Order: Poales
Family: Juncaceae
Genus: Juncus
L.
Type species
Juncus acutus
Synonyms[1]
  • Cephaloxys Desv., illegitimate superfluous name
  • Tristemon Raf. 1838, illegitimate homonym, not Raf. 1819 (Juncaginaceae) nor Klotzsch 1838 (syn of Erica in Ericaceae) nor Scheele 1848 (syn of Cucurbita in Cucurbitaceae)
  • Juncastrum Fourr., not validly published
  • Juncinella Fourr., not validly published
  • Phylloschoenus Fourr., not validly published
  • Tenageia (Dumort.) Fourr.
  • Microschoenus C.B.Clarke

Juncus is a genus of monocotyledonous flowering plants, commonly known as rushes. It is the largest genus in the family Juncaceae, containing around 300 species.[2]

Description

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Rushes of the genus Juncus are herbaceous plants that superficially resemble grasses or sedges.[3] They have historically received little attention from botanists; in his 1819 monograph, James Ebenezer Bicheno described the genus as "obscure and uninviting".[4]

The form of the flower differentiates rushes from grasses or sedges. The flowers of Juncus comprise five whorls of floral parts: three sepals, three petals (or, taken together, six tepals), two to six stamens (in two whorls) and a stigma with three lobes.[3] The stems are round in cross-section, unlike those of sedges,[3] which are typically somewhat triangular in cross-section.[5]

In Juncus section Juncotypus (formerly called Juncus subg. Genuini),[6] which contains some of the most widespread and familiar species, the leaves are reduced to sheaths around the base of the stem and the bract subtending the inflorescence closely resembles a continuation of the stem, giving the appearance that the inflorescence is lateral.[7]

Distribution and ecology

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Juncus has a cosmopolitan distribution, with species found throughout the world, with the exception of Antarctica.[2] They typically grow in cold or wet habitats, and in the tropics, are most common in montane environments.[3]

Fossil record

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Several fossil fruits of a Juncus species have been described from middle Miocene strata of the Fasterholt area near Silkeborg in Central Jutland, Denmark.[8]

Classification

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In Juncus effusus (and other species in J. sect. Juncotypus), the bract appears as a continuation of the stem, and the inflorescence appears lateral.

The genus Juncus was first named by Carl Linnaeus in his 1753 Species Plantarum. The type species of the genus was designated by Frederick Vernon Coville, who in 1913 chose the first species in Linnaeus' account, Juncus acutus.[6] Juncus can be divided into two major groups, one group with cymose inflorescences that include bracteoles, and one with racemose inflorescences with no bracteoles.[6]

The genus is divided into the following subgenera and sections:[6]

  • Juncus subg. Juncus
    • sect. Juncus
    • sect. Graminei (Engelm.) Engelm.
    • sect. Caespitosi Cout.
    • sect. Stygiopsis Kuntze
    • sect. Ozophyllum Dumort.
    • sect. Iridifolii Snogerup & Kirschner
  • Juncus subg. Poiophylli Buchenau
    • sect. Tenageia Dumort.
    • sect. Steirochloa Griseb.
    • sect. Juncotypus Dumort.
    • sect. Forskalina Kuntze

Species

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Selected Juncus species
J. inflexus
J. jacquinii
J. squarrosus
J. trifidus

Plants of the World Online accepts the following species in the genus Juncus:[9]

References

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  1. ^ Kew World Checklist of Selected Plant Families
  2. ^ a b Ralph E. Brooks; Steven E. Clemants (2000). "Juncus". Magnoliophyta: Alismatidae, Arecidae, Commelinidae (in part), and Zingiberidae. Flora of North America. Vol. 22. Oxford University Press. ISBN 0-19-513729-9.
  3. ^ a b c d D. M. D. Yakandawala; U. M. Sirisena; M. D. Dassanayake (2005). "Two new records of Juncus species (rush family – Juncaceae) in Sri Lanka" (PDF). Ceylon Journal of Science. 33: 67–76.
  4. ^ James Ebenezer Bicheno (1819). "XVII. Observations on the Linnean genus Juncus, with the characters of those species, which have been found growing wild in Great Britain". Transactions of the Linnean Society of London. 12 (2): 291–337. doi:10.1111/j.1095-8339.1817.tb00229.x.
  5. ^ Peter W. Ball; A. A. Reznicek; David F. Murray. "210. Cyperaceae Jussieu". In Flora of North America Committee (ed.). Magnoliophyta: Commelinidae (in part): Cyperaceae. Flora of North America. Vol. 23. Oxford University Press. ISBN 978-0-19-515207-4.
  6. ^ a b c d Jan Kirschner; Lázaro J. Novara; Vladimir S. Novikov; Sven Snogerup; Zdeněk Kaplan (1999). "Supraspecific division of the genus Juncus (Juncaceae)". Folia Geobotanica. 34 (3): 377–390. Bibcode:1999FolGe..34..377K. doi:10.1007/BF02912822. JSTOR 4201385. S2CID 31779452.
  7. ^ K. L. Wilson; L. A. S. Johnson (2001). "The genus Juncus (Juncaceae) in Malesia and allied septate-leaved species in adjoining regions". Telopea. 9 (2): 357–397. doi:10.7751/telopea20013009.
  8. ^ Angiosperm Fruits and Seeds from the Middle Miocene of Jutland (Denmark) by Else Marie Friis, The Royal Danish Academy of Sciences and Letters 24:3, 1985
  9. ^ "Juncus L." Plants of the World Online. Board of Trustees of the Royal Botanic Gardens, Kew. 2017. Retrieved 22 January 2021.
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