Castor bean (Ricinus communis).
Description:
R. communis is a robust perennial shrub that typically reaches heights of 3-5 metres. It has large, palmately lobed leaves and sharply toothed leaf margins. The large (10 to 75cm across), umbrella-like leaves have 5 to 9 pointed, fingerlike lobes. Long purple leaf-stems are attached near the centers of the leaf blades. The leaves are usually deep green, but in some strains they have a reddish cast. They have an odor when crushed. The stems are smooth, round, and frequently red, with clear sap. The flowers are small and greenish, with both male and female flowers on the same plant. The fruit is a quarter-sized, three-lobed, round, spiny capsule, often green or red, containing up to three shiny, smooth, mottled seeds that resemble ticks. One large, mottled, attractive seed develops in each lobe. The flowers are male and female on the same plant, and are produced on a clustered, oblong, terminal spike. The male flowers are placed on the under portion of the spike; they have no corolla, only a green calyx, deeply cut into three to five segments, enclosing numerous, much branched, yellow stamens. The female flowers occupy the upper part of the spike and have likewise no corolla. The three narrow segments of the calyx are, however, of a reddish colour and the ovary in their centre is crowned by deeply divided, carmine-red threads (styles). The fruit is a blunt, greenish, deeply grooved capsule less than 2.5cm long, covered with soft, yielding prickles in each of which a seed is developed.
R. communis is herbaceous when young but in frost-free areas it can be an evergreen tree that gets up to 12m in height and become woody with age. The wood is soft and light with a thick central pith. Occasionally, irregular brown heartwood develops. The bark is light brown, smooth, and exhibits rings at the nodes and raised lenticels. There are a moderate number of large, star-shaped leaves with 7 to 9 long pointed lobes.
Occurs in:
Agricultural areas, coastland, riparian zones, ruderal/disturbed.
Castor bean (Ricinus communis) Distribution in North America shown in green.
Habitat description:
R. communis is frequently found in riparian areas, especially along the south and central coast, where it invades and displaces native vegetation. This plant is also common as an escape in abandoned fields, drainages, ditches, and along roadsides and railroad tracks. It is killed by low temperatures, and as little as twenty-four hours at 2 degrees F is sufficient to produce visible impacts on cellular membranes of seedlings at any stage of germination. Distribution is limited by castor bean’s intolerance of cold temperatures. It is tolerant of a wide range of soil types and conditions. Plants tend to germinate more profusely in full sun. Disturbance required if natural stands of R. communis are to successfully establish. If disturbance is not repeated, R. communis will be succeeded in a few years by grass, vines, or trees. It is competitive and most frequently seen in flood zones, on neglected farmland, and roadsides.
General impacts:
Castor bean displaces native plant species in riparian areas and drainages. Its seeds are among the first to germinate following fire. Plants colonize disturbed areas, and they grow rapidly, shading out native seeds and seedlings and producing monospecific stands in areas with previously healthy native vegetation. Humans and horses are especially vulnerable to R. communis seeds if they are chewed on when ingested. Fatal doses are from 2.5 to 6 seeds for humans and about 6 seeds for horses. Symptoms are stomach irritation, diarrhea, abdominal pain, increased heart rate, profuse sweating, collapse, and convulsions. Broken seeds can cause skin irritation. The foliage is only slightly toxic. Seeds that are ingested but not chewed will likely pass through the body harmlessly.
Geographical range:
Close up of the Castor bean (Ricinus communis) Weed.
Native range: R. communis was originally native to northeastern Africa and the Middle East.
Known introduced range: Australasia-Pacific, Asia, Europe, North America, and South America.
Management information:
When R. communis becomes weedy in neglected cropland and pasture it is matter of controling the invasive through cultivation and mowing, but in more difficult or sensitive environments Tunison and Zimmer suggest cutting the stump of mature R. communis and applying the herbicide “Banvel” along with the mechanical control techniques of uprooting seedling. The authors report that Banvel was nearly 100% effective. Langeland and Stocker also suggest treating R. communis with either basal bark or cut-stump methods followed by an application with 10% Garlon 4, but the authors reiterate that the site must be revisited several times after the initial herbicide treatment to hand pull seedlings that sprout.
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