> Home | Alerts archive | Ononis alopecuroides
Weed Alert!

Ononis alopecuroides
(Restharrow)


Summary: new plant of unknown characters
Ononis alopecuroides has been found in San Luis Obispo County, California. A dense, but relatively localized colony occupies approximately half an acre in open grazed woodland-savanna (Quercus agrifolia and Pinus sabiniana). The colony extends eastward down a dry arroyo to the edge of the riparian zone next to Suey Creek. G. Frederic Hrusa, Senior Plant Systematist for the California Department of Food and Agriculture believes that this colony will continue to expand if current control efforts are unsuccessful. This is the first record of O. alopecuroides in North America. How the colony came to be here is unknown. Hrusa believes that it may have been a contaminant in Trifolium seed since the two seeds look similar. Currently, this colony is the target of eradication measures by the San Luis Obispo County Agricultural Commissioners Office.

Description:
(Click on thumbnail images for a closer view)

Flowers

Fruiting spike

Plants

Infestation
Ononis alopecuroides L. (Fabaceae) is a heavily branched woody annual 0.5-1 m in height. The lower plant stems are glabrous while the upper stems are glandular and hairy. Young seedlings often have unifoliate leaves. Leaves on mature plants are trifoliate with the lateral leaflets reduced in size compared to the terminal leaflet. The leaflets are edged with tiny teeth and are elliptical or elliptic-orbicular in shape and glabrous. The flowers are borne singly at each node, and form dense terminal spikes. The corolla (13-16 mm wide) is pink and is as long as (or longer than) the tubular calyx. The seed-pod of O. alopecuroides is 8-10 mm in length and contains 2-3 seeds. Each seed is 2-3 mm long, orange-brown, smooth and shiny.

Germination occurs in the early spring. In 1998, seedlings germinated in late March at the San Luis Obispo Co. site. However, it was an "El Nino year" and spring occured later than usual. Flowering begins quite soon after maturity. Greenhouse-grown plants (from seedlings dug from the San Luis Obispo Co.) were fully flowering by June 1. The plant population at the San Luis Obispo Co. site were mature and nearly ready to disperse seed in early July.

Scientific and Common Names:
The genus Ononis is large, and O. alopecuroides L. is one of several similar species in a confusing complex. Other species in this complex are Ononis salzmanniana Boiss. & Reuter and Ononis baetica Roxas Clemente & Rubio. Some authors consider some of these names to be synonomous with O. alopecuroides. The genus name Ononis was coined because the plant is purported to be a favorite food of donkeys (Greek: onos). The common name "Restharrow" was derived from the fact that the long, thick root masses will "arrest the progress of the harrow."

Impacts and Considerations:
The impacts of this new invader are unknown. However, O. alopecuroides has the following characteristics.
1)It is considered weedy in northern Europe (where it is not native).
2)It invades disturbed or dry/rocky areas.
3)It forms dense stands that are capable of excluding other vegetation.
4)Plants appear to be unpalatable to the horses and burros that graze within the San Luis Obispo site.
5)The rapid production of many seeds suggests that established O. alopecuroides populations will be difficult to eradicate.

Native Range:
Ononis alopecuroides is native to the western Mediterranean region, northern Africa, and southern Europe.

Range As An Invader:
Ononis alopecuroides is occasionally weedy in northern and central Europe. The occurrence of O. alopecuroides in southern San Luis Obispo County, California is the first record for North America. O. alopecuroides grows best in moist areas receiving full sun. Sunny, dry areas tend to have smaller plants (0.3 m compared to 1.5 m tall and 1.5 m wide). Plants are not found in shady areas, even if the soil is moist.

Control:
Little is known on the control of this new invader.
1)It is an annual, so the focus must be on reducing or stopping seed production.
2)The rootstock is weak and easily pulled from the ground.
3)A 2% solution of glyphosate (e.g. Roundup) was effective on seedlings. Apply herbicide before flowering. Glyphosate is a nonselective herbicide, so it should be used with care to prevent damaging non-target plants.

References:
1)Flora Europaea Vol. 2 (eds. T.G. Tutin, V. H. Heywood, N.A. Burges, D.M. Moore, D.H. Valentine, S.M. Walters, and D.A. Webb), 1968, Cambridge University Press, Great Britain, p. 148.
2)G. Frederick Hrusa, CDFA Herbarium, personal communication.
3)G. Perez, San Luis Obispo County Agricultural Comissioners Office, personal communication.
4)Botanical.com
5)W3 Tropicos (Missouri Botanical Gardens)

--Tunyalee Martin/Wildland Invasive Species Team; December 1999



Updated January 2005
©The Nature Conservancy, 1999