Juncus compressus — round-fruited rush
![Inflorescences: Juncus compressus. ~ By Steve Garske. ~ Copyright © 2024 Steve Garske. ~ asimina[at]alphacomm.net](https://newfs.s3.amazonaws.com/taxon-images-1000s1000/Juncaceae/juncus-compressus-in-sgarske.jpg)
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Facts
Round-fruited rush is an exotic rush native to Europe and western Asia. In New England, it colonizes disturbed areas with saline soil. In other parts of its North American range it favors calcareous wetlands, which could bring it into contact with rare native species.
Habitat
Anthropogenic (man-made or disturbed habitats)
New England distribution
Adapted from BONAP data
Native: indigenous.
Non-native: introduced (intentionally or unintentionally); has become naturalized.
County documented: documented to exist in the county by evidence (herbarium specimen, photograph). Also covers those considered historical (not seen in 20 years).
State documented: documented to exist in the state, but not documented to a county within the state. Also covers those considered historical (not seen in 20 years).
Note: when native and non-native populations both exist in a county, only native status is shown on the map.
Found this plant? Take a photo and post a sighting.
enlargeCharacteristics
- Habitat
-
- terrestrial
- wetlands
- New England state
-
- Maine
- Vermont
- Stem shape in cross-section
- the stem is round or oval in cross-section
- Leaf blade width
- 0.8–2 mm
- Leaf blade cross-section
- the leaf blade is flat or rolled in at the edges
- Inflorescence position
- the inflorescence is at the tip of the plant
- Inflorescence branching
- the inflorescence is branched
- Fruit type (general)
- the fruit is a capsule, with at least three seeds in it
- Fruit length
- 2.5–3.5 mm
- Leaf position on plant
- some leaf attachment points are above the midpoint of the stem
- Perianth composition
- the perianth is green or brown, with six sepal-like parts, and a leafy texture
- Fruit cross-section
- the fruit is triangular to terete (circular) in cross-section
-
Flowers
- Anther color (dry)
- the anthers range in color from white to tan or yellow to yellow-brown
- Anther length
- 0.6–1 mm
- Floral bristle color
- NA
- Floral bristle number
- NA
- Floral bristle relative length
- NA
- Floral bristles
- NA
- Floral scale hairs
- NA
- Floral scale length
- 0 mm
- Floral scale nerves
- NA
- Flower number per cluster
-
- 5-20
- more than 20
- Inflorescence bract angle
- the bracts are vertical or angled only slightly outwards
- Inflorescence bract number
- there are two to five bracts per inflorescence
- Inflorescence bract position (Sparganium)
- NA
- Inflorescence bracts
- there are at least two bracts, and they are either flat or folded or rolled in at the edges
- Inflorescence branching
- the inflorescence is branched
- Inflorescence crowding
-
- the inflorescence is at least somewhat spread out, with at least one branch coming from the main stem
- the inflorescence is crowded together in one tight cluster
- Inflorescence position
- the inflorescence is at the tip of the plant
- Inflorescence shape
- the aggregations within the inflorescence are roughly circular (not flattened) in cross-section
- Inflorescence type
- there are two or more flowers, spikes or flower clusters on a branched inflorescence
- Perianth composition
- the perianth is green or brown, with six sepal-like parts, and a leafy texture
- Stamen length
- 1.1–1.7 mm
- Stamen number
- 4-6
- Stigma number
- 3
- floral bristle barbs
- NA
-
Fruits or seeds
- Achene beak length
- 0 mm
- Achene surface texture
- NA
- Achene tubercle relative width
- NA
- Achene tubercle width
- 0 mm
- Capsule relative length
- the capsule is longer thant he perianth
- Fruit cross-section
- the fruit is triangular to terete (circular) in cross-section
- Fruit length
- 2.5–3.5 mm
- Fruit type (general)
- the fruit is a capsule, with at least three seeds in it
- Fruit type (specific)
- the fruit is a capsule (splits along two or more seams, apical teeth or pores when dry, to release two or more seeds)
- Locules in capsule
- the three internal walls do not meet in the center
- Seed length
- 0.35–0.556 mm
- Seed tail relative length
- 0.3–0.6 mm
- Seed tails
- there is no tail on the seeds
- Tubercle height
- 0 mm
-
Growth form
- Lifespan
- the plant lives more than two years
- Underground organs
- the plant has a rhizome (a horizontal underground stem with roots growing from it)
-
Leaves
- Auricle length
- 0.3–0.5 mm
- Auricle texture
- the auricles are weak, papery and translucent
- Auricles
- the leaf sheath has auricles on it
- Leaf blade cross-section
- the leaf blade is flat or rolled in at the edges
- Leaf blade length
- 50–350 mm
- Leaf blade width
- 0.8–2 mm
- Leaf form
- all the leaves hold their form out of water
- Leaf position on plant
- some leaf attachment points are above the midpoint of the stem
- Leaf septa
- the leaf blades do not have transverse septa
- Leaf sheath hairs
- the leaf sheathes are without hairs
- Pedicel length (Typha)
- 0 mm
- Stem leaf blade ligules
- there are no ligules at the leaf blade bases
- Stem leaf blades
- there are fully-developed leaves with leaf blades on the main stem
-
Place
- Habitat
-
- terrestrial
- wetlands
- New England state
-
- Maine
- Vermont
- Specific habitat
- man-made or disturbed habitats
-
Stem, shoot, branch
- Plant height
- 10–80 cm
- Stem shape in cross-section
- the stem is round or oval in cross-section
- Stem texture near tip
- the stem feels smooth near the tip
Wetland status
Usually occurs in wetlands, but occasionally in non-wetlands. (Wetland indicator code: FACW)
In New England
Distribution
- Connecticut
- absent
- Maine
- present
- Massachusetts
- absent
- New Hampshire
- absent
- Rhode Island
- absent
- Vermont
- present
Conservation status
None
From Flora Novae Angliae dichotomous key
13. Juncus compressus Jacq. E
round-fruited rush. ME, VT. Shoulders and ditches of salted roadways, railroad embankments, disturbed saline soil.
Native to North America?
No
Sometimes confused with
- Juncus gerardii:
- anthers mostly 1.1–1.6 mm long, 2–4 times as long as the filament, and primary bract of the inflorescence mostly 1–5 cm long, usually not conspicuously exceeding the inflorescence (vs. J. compressus, with anthers 0.6–1 mm long, 1–2 times as long as the filament, and primary bract of the inflorescence mostly 2–7.5 cm long, often conspicuously exceeding the inflorescence).