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)
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
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]
In 2013 the genus Oreojuncus was separated from Juncus. In 2022 Viktorie Brožová et al. published a phylogenetic analysis of the cyperids (families Juncaceae, Cyperaceae, and Thurniaceae) which found Juncus to be paraphyletic, and the authors proposed that six new genera, Alpinojuncus, Agathryon, Australojuncus, Boreojuncus, Juncinella, and Verojuncus, be split from Juncus.[9] As of July 2025 Plants of the World Online accepts Juncinella but treats the others as synonyms of Juncus.[1]
↑ 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
↑ Viktorie Brožová, Jarosław Proćków, Lenka Záveská Drábková, Toward finally unraveling the phylogenetic relationships of Juncaceae with respect to another cyperid family, Cyperaceae. Molecular Phylogenetics and Evolution, Volume 177, 2022, 107588, ISSN 1055-7903, https://doi.org/10.1016/j.ympev.2022.107588.
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