This is one of the smallest species of Juncus in the state, reflected in the species name meaning "weak." Many populations may be undiscovered because of its resemblance to Juncus brachycarpus, Juncus acuminatus and Juncus subcaudatus.
There are four existing populations but only one of them is of good quality. The other three have less than 60 plants each and are under some threat by human disturbance. There are five historical occurrences but most of them are too vague for targeted searches.
Short-term trends are not well known since only one population has been revisited in recent years and the plants were extirpated by changes in habitat. This plant occurs in habitats that could undergo change in a short time.
This plant has only ever had five or fewer occurrences in New York at any one time. Some historical occurrences are too vague to know whether they still exist and others are from locations where the habitat probably no longer exists. As some locations are lost and others are discovered the plant will probably continue to exist in small numbers in the state.
One population is around a lake where it can be trampled by people fishing and walking.
Make sure the plants are protected from human impacts.
Research is needed to discover what limits the distribution of this plant in New York since there are many wet shorelines where it could live.
Juncus debilis has been collected from a rather broad variety of habitats in New York, including red maple swamps, mudflats, shallow emergent marshes, and coastal plain pond shores. More information on the habitat requirements of this small and possibly overlooked species in the state is needed (New York Natural Heritage Program 2007). Wet places, shores, etc. (Fernald 1970). Moist sandy soil (Gleason & Cronquist 1991).
In New York Juncus debilis is known only from Long Island, the Hudson Highlands west of the Hudson River, and along the Delaware River.
Juncus debilis reaches to northern tip of its range in far southern New York, New Jersey, and eastern Pennsylvania. From there its distribution arcs southwest, including the coastal states to northern Florida and eastern Texas, as well as Kentucky, Tennessee, Illinois, Missouri, and Arkansas in the interior.
Weak Rush is a tufted, grass-like perennial. Its stems are erect, round, smooth, and only 10 to 25 cm tall and 1-2mm wide. There are 1-3 dark green to purplish leaves along the stem, from 1 to 12.5 cm long and .5 to 1.5 mm wide. The flowers are borne in 3 to 35 heads on widely-spreading branches, each head with from 2-10 (20) flowers. As with all rushes, each flower has 6 tepals (reduced petal-like structures); in J. debilis these are green to straw-colored, up to 2.3 mm long, and have pointed tips. The fruit are capsules 2.8 to 3.7 mm long, exceeding the length of the perianth (tepals).
This species is best identifed when mature fruit are present.
Juncus acuminatus and J. brachycarpus each have tepals which are much longer than the fruit. J. subcaudatus has seeds .7 to 2.6 mm long, each with a tail and a white translucent veil, while those of J. debilis are only .3 to .4 mm long and lack tails or veils (FNA 2000).
The fruits on this species ripen in late July or early August and can persist into the fall.
The time of year you would expect to find Weak Rush fruiting in New York.
Juncus debilis Gray
Flora of North America Editorial Committee. 2000. Flora of North America north of Mexico. Vol. 22. Magnoliophyta: Alismatidae, Arecidae, Commelinidae (in part), and Zingiberidae. Oxford Univ. Press, New York. xxiii + 352 pp.
Clemants, Steven E. 1990. Juncaceae (rush family) of New York State. Contributions to a flora of New York State VII Richard S. Mitchell, ed. New York State Museum Bulletin No. 475. 67 pp.
Crow, Garrett E. and C. Barre Hellquist. 2000. Aquatic and Wetland Plants of Northeastern North America: A revised and enlarged edition of Norman C. Fassett's a Manual of Aquatic Plants. Volume One: Pteridophytes, Gymnosperms, and Angiosperms: Dicotyledons. The University of Wisconsin Press. Madison, Wisconsin. 536 Pages.
Fernald, M.L. 1950. Gray's manual of botany. 8th edition. D. Van Nostrand, New York. 1632 pp.
Gleason, Henry A. and A. Cronquist. 1991. Manual of Vascular Plants of Northeastern United States and Adjacent Canada. The New York Botanical Garden, Bronx, New York. 910 pp.
Holmgren, Noel. 1998. The Illustrated Companion to Gleason and Cronquist's Manual. Illustrations of the Vascular Plants of Northeastern United States and Adjacent Canada. The New York Botanical Garden, Bronx, New York.
New York Natural Heritage Program. 2010. Biotics database. New York Natural Heritage Program. New York State Department of Environmental Conservation. Albany, NY.
New York Natural Heritage Program. 2023. New York Natural Heritage Program Databases. Albany, NY.
Rhoads, Ann F. and Timothy A. Block. 2000. The Plants of Pennsylvania, an Illustrated Manual. University of Pennsylvania Press, Philadelphia, PA.
Weldy, T. and D. Werier. 2010. New York flora atlas. [S.M. Landry, K.N. Campbell, and L.D. Mabe (original application development), Florida Center for Community Design and Research http://www.fccdr.usf.edu/. University of South Florida http://www.usf.edu/]. New York Flora Association http://newyork.plantatlas.usf.edu/, Albany, New York
Weldy, Troy W. and David Werier. 2005. New York Flora Atlas. [S.M. Landry, K.N. Campbell, and L.D. Mabe (original application development), Florida Center for Community Design and Research. University of South Florida]. New York Flora Association, Albany, NY. Available on the web at (http://newyork.plantatlas.usf.edu/).
Information for this guide was last updated on: January 18, 2008
Please cite this page as:
New York Natural Heritage Program. 2023. Online Conservation Guide for Juncus debilis. Available from: https://guides.nynhp.org/weak-rush/. Accessed January 29, 2023.