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Weed Alert!

Coincya monensis (L.) Greuter and Burdet
(Isle of Man cabbage, coincya, star mustard)

Summary: new plant of unknown characters
Coincya monensis was first discovered in California in late February 1997 by Jim Belsher, a graduate student at Humboldt State University. The plants were growing next to the Manila Community Services District's treatment ponds, and occupied 2 acres in a pasture on fill and in disturbed dunes. It is not known how this population was introduced into Humboldt County, but it may have been brought in on construction equipment, with imported fill, or in horse manure.

Efforts are currently underway to prevent this species from invading nearby natural dunes and to eliminate the entire population if possible. The sand-verbena-beach bursage series and native dunegrass series plant communities are seriously threatened by invasive plants. Two federally listed species, Erysimum menziesii subsp. eurekense (Humboldt bay wallflower) and Layia carnosa (beach layia) reside in the nearby natural dunes.

(Click on thumbnail images for a closer view)

Basal rosette

Dune invaders


Beaked fruit

(Photographs by Andrea Pickart; andrea_pickart(at)mail.fws.gov)

Coincya monensis (L.) Greuter and Burdet is a medium sized herbaceous plant from the mustard family. Stems are prostrate to erect, branched, and up to 1m tall. Leaves (5-22 cm long x 0.5-8 cm wide) are glaucous with dentate lobes. The amount of lobing on the leaves decreases from the base of the plant to the base of the racemose inflorescence. Flowers have bright yellow petals with pale brown or violet veins. There are no bracts on the inflorescences. The fruit has 3-5 veined valves and a flat, 1-6 seeded beak. The entire, mature fruit is 3.5-8.5 cm in length. The fruiting pedicel is rarely erect. The fruit contains a single row of 8-10 seeds. Seeds are subspherical to oblong and can be black or brown in color.

The fruiting C. monensis plants growing in Humboldt Co., California ranged from 4 cm to 1 m tall. Basal rosettes varied from 2 to 40 cm in diameter. In contrast to the description above, they were not glaucous and not all lacked inflorescence bracts--these features of the species can apparently be quite variable.

Coincya is very similar to a number of other mustards found in eastern North America. It can be distinguished from the genus Brassica by the venation on the fruit--the valves on Brassica fruit have but one vein while Coincya has 3-5 veins. Plants in the genus Erucastrum have bracteate inflorescences and a style-like, 4 mm long beak on fruits. In contrast, Coincya inflorescences generally lack bracts, and the fruit-beaks are broad and somewhat flattened. While the flowers of Sinapis has uniformly colored petals and spreading sepals, Coincya petals have colored veins and the sepals are erect and converging.

Coincya monensis can be an annual or a perennial. Although most plants appear to be annuals in California, some plants were found to be perennial. In Pennsylvania plants may live 2-3 years and set seeds each year. The blooming period for C. monensis is long and lasts from late April to October. Some plants in Humboldt Co., California were observed setting seed on April 8, 1997 and dehisced between April 8 and April 14, 1997. In 1998 the plants bloomed earlier and were observed in fruit and dispersing seeds on March 19.

Scientific and Common Names:
The taxonomy and nomenclature of the genus Coincya is in dispute (see Leadlay & Heywood, 1990; Kartesz & Gandhi, 1994; and Rollins, 1961, 1993). Synonyms for C. monensisinclude: "Brassica monensis (L.) Hudson", "Erucastrum monensis (L.) Link", "Sinapis monensis (L.) Bab.", "Brassicella menensis (L.) O.E. Schulz", "Rhynchosinapis monensis (L.)", and "Hutera monensis (L.) Gomez-Campo". The five subspecies of C. monensis have over 129 synonyms. An excellent discussion of the situation is in Naczi & Thieret (1996).

The impacts of this new invader are unknown. However, C. monensis has the following characteristics.
1)It is a pioneering species in open habitats of western Europe.
2)It is extremely invasive in Pennsylvania and other states in the eastern USA.
3)Its spread in Pennsylvania has been rapid (twenty counties in 3 decades).
4)It is commonly found in disturbed areas such as fields, trails, alongside roads, and railroad tracks. It is also found in maritime sands, along sandy rivers, and steep, rocky areas and on cliffs (0-3200 m).
5)It can grow in extremely rocky and gravelly areas.
6)Large, dense stands may exclude other species.

Native Range:
Coincya monensis is native to Corsica, France, Germany, Great Britain, Italy, Morocco, Portugal, and Spain.

Range As An Invader:
This species has been found in five areas of the eastern USA, one of these in the late 1800s only, and the other four since the 1950s (Naczi & Thieret, 1996). The first USA detection was around ballast dumps near Philadelphia and Hoboken. C. monensis (then called "Brassica monensis" or "B. cheiranthus") was apparently transported via ship ballast. Fully established populations were not detected until 1958, when it was found in far western North Carolina (Yancey County), where it still persists. In 1964, C. monensis was found in Luzerne County, Pennsylvania. Collections made in the 1990s have documented its spread to 19 other counties in Pennsylvania. C. monensis is now spreading from Pennsylvania into southern New York. C. monensis has also been found in southwestern Michigan and Kentucky. The sources of these infestations are unknown, and it appears that there have been several long-distance dispersal and introduction events. Other states may have populations of C. monensis that have been undetected because of the plant's similarity to other weedy mustards.

In Europe C. monensis occurs from hardiness zone 10 (-1.1 to 4.4C minimum temperature) to zone 7 (-17.8 to -12.2C minimum temperature). However, in North America, the plant has become established in zone 5 areas (minimum temperature of -28.9 to -23.3C).

Little is known on the control of this new invader.
1)Except for a tap root, the roots are shallow and the plants are easily hand-pulled.
2)Monitor yearly, no later than late February to remove plants before fruits are formed.
3)It is an annual, so the focus must be on reducing or stopping seed production.

1)Kartesz, J.T. and K.N. Gandhi. 1994. Nomenclatural notes for the North American flora. XIII. Phytologia 76:441-457.
2)Leadlay, E.A. and V.H. Heywood. 1990. The biology and systematics of the genus Coincya Porta and Rigo ex Rouy (Cruciferae). J. Linn. Soc. Bot. 102:313-398.
3)Naczi, R.F.C. and J.W. Thieret. 1996. Invasion and spread of Coincya monensis (Brassicaceae) in North America. Sida 17(1):43-53.
4)Pickart, A. 1997. A New Invasive Mustard in California. CalEPPC News Fall:6
5)Rollins, R.C. 1961. A weedy crucifer again reaches North America. Rhodora 63:345-346.
6)Rollins, R.C. 1993. The Cruciferae of continental North America. Stanford University Press, Stanford, California.

--Tunyalee Martin/Wildland Invasive Species Team; January 2000

Updated January 2005
©The Nature Conservancy, 2000