Juncus


Juncus is a genus of monocotyledonous flowering plants, commonly known as rushes. It is the largest genus in the family Juncaceae, containing around 340 species.

Description

Rushes of the genus Juncus are herbaceous plants that superficially resemble grasses or sedges. They have historically received little attention from botanists; in his 1819 monograph, James Ebenezer Bicheno described the genus as "obscure and uninviting".
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, two to six stamens and a stigma with three lobes. The stems are round in cross-section, unlike those of sedges, which are typically somewhat triangular in cross-section.
In Juncus section Juncotypus, 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.

Distribution and ecology

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

Fossil record

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

Classification

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. Juncus can be divided into two major groups, one group with cymose inflorescences that include bracteoles, and one with racemose inflorescences with no bracteoles.
In 2013 the genus Oreojuncus was separated from Juncus. In 2022 Viktorie Brožová et al. published a phylogenetic analysis of the cyperids 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. Plants of the World Online accepts Juncinella but treats the others as synonyms of Juncus.
The genus is divided into the following subgenera and sections:Juncus subg. Juncus
  • * sect. Juncus
  • * sect. Graminei
  • * sect. Caespitosi
  • * sect. Stygiopsis
  • * sect. Ozophyllum
  • * sect. Iridifolii Juncus subg. Poiophylli
  • * sect. Tenageia
  • * sect. Steirochloa
  • * sect. Juncotypus
  • * sect. ''Forskalina''

Species

As of July 2025, Plants of the World Online accepts 342 species:

Formerly placed here