Sonchus L. is a genus of approximately 106 flowering plants in the family Asteraceae (tribe Cichorieae, subfamily Cichorioideae), commonly known as sow thistles. Authored by Carl Linnaeus, the type species is Sonchus oleraceus. The genus contains four recognized subgenera, including Dendroseris and Dendrosonchus.
Plants are mostly annual or perennial herbs, though some woody varieties exist in island lineages. Mature stems typically reach 30 cm to 2 meters in height depending on the species. Leaves are soft, irregularly lobed, and clasp the stem; younger plants form basal rosettes. A characteristic feature of the genus is the milky latex exuded from all plant parts when damaged. Flower heads are yellow and range from roughly half to one inch in diameter; mature fruits are single-seeded achenes dispersed by a feathery pappus similar to a dandelion's.
The genus is native to Eurasia and tropical Africa and has spread widely across temperate regions worldwide, commonly found along roadsides, in disturbed habitats, arable fields, ditches, and waste ground. Several species — notably Sonchus arvensis — are significant agricultural weeds capable of depleting soil nitrogen and water, and are not easily eradicated by mowing alone for all species. The plants serve as host plants for aphids and Lepidoptera larvae but also attract beneficial insects such as hoverflies, making some gardeners value them as sacrificial companion plants.
Etymology
The genus name Sonchus derives from the Ancient Greek σόγχος (sonchos), the classical name applied to plants of this type. The familiar common name "sow thistle" traces to an old agricultural tradition: the plants were fed to lactating pigs in the belief that they enhanced milk production.
Distribution
Sonchus is native to Eurasia and tropical Africa. Through deliberate introduction and accidental dispersal, it has naturalized across temperate regions worldwide. In North America it occurs throughout the coastal, piedmont, and mountain regions of North Carolina, and is widely recorded elsewhere across USDA hardiness zones 6b–9b. In Europe, Swiss records document five species with distributions across lowland and montane habitats. Within the genus, Sonchus arvensis (including subspecies arvensis and uliginosus) and Sonchus asper are among the most broadly distributed species.
Ecology
Sow thistles are highly adaptable, colonizing roadsides, arable fields, waste ground, ditches, and brackish margins. Several species — most prominently Sonchus arvensis — function as persistent agricultural weeds that deplete soil nitrogen and water reserves. Control by mowing is effective for some species as they do not regrow readily from root fragments, though the perennial S. arvensis is more resilient. The plants serve as important host plants for aphids and Lepidoptera larvae. At the same time, aphid colonies on sow thistles attract beneficial predatory insects including hoverflies, which has led some growers to use them deliberately as sacrificial companion plants alongside onions, tomatoes, and cucurbits. The genus also functions as a dynamic accumulator.
Cultivation
Most Sonchus species require little deliberate cultivation and establish readily in disturbed soils. Where grown intentionally, they tolerate a wide range of soil textures — light (sandy), medium (loamy), and heavy (clay) — and a pH range from mildly acid to mildly alkaline, including saline conditions. Full sun to semi-shade is acceptable, and moist conditions are preferred. Plants are self-fertile. Some species are valued in gardens as sacrificial or companion plants to lure aphids away from crops.
Cultural Uses
Sonchus species have a long history of use as food and medicine across multiple cultures. Young leaves can be eaten raw in salads, with a flavor described as similar to lettuce; cooked, they resemble chard. Stems can be prepared like asparagus once the outer skin is removed, young roots are edible when cooked, and roasted roots have been used as a coffee substitute. Nutritionally, leaves of Sonchus arvensis contain approximately 47 mg of vitamin C per 100 g and around 2% protein on a dry-weight basis. The plants have also been fed to livestock.
In New Zealand, Sonchus oleraceus is known in Maori as pūhā and has been a traditional green vegetable used in hangi (earth oven cooking) and other preparations, representing one of the most culturally significant introduced plants in Maori cuisine.
In traditional medicine, leaf poultices have been applied for their anti-inflammatory properties, leaf infusions used to address breast engorgement, and root preparations used for respiratory ailments including asthma and coughs.
Taxonomy
Sonchus was formally described by Carl Linnaeus, with Sonchus oleraceus serving as the type species. As of March 2023, the genus comprises approximately 106 accepted species and is divided into four subgenera, among them Dendroseris and Dendrosonchus. It is placed in the tribe Cichorieae within subfamily Cichorioideae of family Asteraceae. Info Flora records the genus under Checklist 1044649 in the Swiss flora system. In Switzerland, five species are documented: S. arvensis, S. asper, S. oleraceus, S. palustris, and S. tenerrimus.
Propagation
Sonchus species propagate primarily by seed. Seeds are equipped with a pappus structure enabling wind and water dispersal, contributing to their wide distribution. For deliberate cultivation, seeds are sown in spring in situ. Most species do not regrow reliably from root fragments, making seed the principal means of spread and establishment.
