Sonchus arvensis

Name and classification

Sonchus arvensis L.
Family Asteraceae, Tribe Cichoreae

NOTE: This species is actionable only when found in field or vegetable seed for planting; tolerance applies.

Common names

perennial sowthistle, field sowthistle

Disseminule

fruit

Description

Fruit an achene, flattened, narrowly elliptical to oblong in outline, frequently slightly curved, (1.8)2.4–4.5 mm long, 0.6–1.4 mm wide, 0.3–0.6 mm thick, narrowly elliptical in cross section; both ends truncate. Covered with ca. 10–16 prominent longitudinal ribs; ribs cross-grooved, appearing tubercled. Dark brown to light- and reddish-brown, dull to faintly glistening. Scar a round, slightly oblique, 4-segmented collar, rim and cavity cream colored. Apex horizontal, a +/– oval ring, cream colored, surrounding slender whitish style base variable in appearance or inconspicuous. Pappus of numerous white hairs, 1.5 cm long, +/– persistent. Embryo straight, spatulate; endosperm absent.

Identification considerations

Sonchus arvensis can be distinguished from Sonchus oleraceus by its deeper and more prominent ribs, and because it lacks the two distinct narrow longitudinal grooves present on each side of Sonchus oleraceus .

Similar species

Sonchus oleraceus L. (non-FNW)

Distribution

widely distributed in temperate regions of the world

native to Europe and temperate regions of western Asia and North Africa

Habitat

temperate and subtropical, humid climates; prefers moist to very wet fertile soils; on pond and river margins, moist meadows, disturbed sites

General information

Sonchus arvensis is a deep-rooted perennial herb, up to 2 m tall. It has been in the U.S. for 150 years. A weed of many crops, this species is a particularly serious weed of cereals. It can rapidly colonize new sites by means of its extensive horizontal and vertical root system. New shoots arise from buds on horizontal roots (including easily broken pieces of roots). Achenes are dispersed by wind, water, and by clinging to animals. Leaves contain a bitter tasting, milky sap. Sonchus arvensis is one of ten species covered under the Federal Seed Act for which tolerance is applicable to its introduction (7 CFR 361.6(a)(2)).

achenes

achenes

achene with pappus

achene with pappus

apex of achene

apex of achene

scar of achene

scar of achene

detail of ridged surface of achene

detail of ridged surface of achene

longitudinal section of achene showing embryo (left) and naked embryo (right)

longitudinal section of achene showing embryo (left) and naked embryo (right)