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Sonchus arvensis
Sonchus arvensis subspecies uliginosusSynonyms: Sonchus uliginosus, Sonchus arvensis variety uliginosus(Field Sow-thistle)
Asteraceae (Sunflower Family)

Moist meadows, disturbed sites, openings. Summer, fall.
Bolam Pass Road, west side, September 11, 2015.

This wide-spread (see the map below) non-native plant grows to over three feet tall (as pictured above) and often spreads from roots into small colonies of plants.

The plant is native to Europe and the genus and species were named by Linnaeus in 1753 from specimens collected in Europe.

Some modern floras consider uliginosus a species, some a variety, and some a subspecies. Some modern floras indicate that Sonchus arvensis is always glandular; other floras indicate that it can be glandular or not. All floras I have checked indicate that the species occurs no higher than 9,000 feet, but the photographs were taken at 10,000. And finally, no floras show the plant occurring in Dolores County, Colorado, where these photographs were taken.

"Sonchus" is Greek for "thistle" and "arvensis" means "of the field". "Ulig" is Latin for "moisture" and "osus" is Latin for "abundant". 

Sonchus arvensis subspecies uliginosus
Sonchus arvensis subspecies uliginosusSynonyms: Sonchus uliginosus, Sonchus arvensis variety uliginosus(Field Sow-thistle)
Asteraceae (Sunflower Family)

Moist meadows, disturbed sites, openings. Summer, fall.
Bolam Pass Road, west side, September 11, 2015.

Flowers are yellow/orange, large, and attractive  --  even if the plant is noxious. As the photographs show, flowering stems split several times producing a panicle of flowers. Flower heads contain only ray flowers (as do Taraxacum, Dandelions).

 

Sonchus arvensis subspecies uliginosus

Sonchus arvensis subspecies uliginosusSynonyms: Sonchus uliginosus, Sonchus arvensis variety uliginosus(Field Sow-thistle)
Asteraceae (Sunflower Family)

Moist meadows, disturbed sites, openings. Summer, fall.
Bolam Pass Road, west side, September 11, 2015.

Note the shape of the involucre and that it is glabrous (smooth, without hairs).

Sonchus arvensis subspecies uliginosus

Sonchus arvensis subspecies uliginosusSynonyms: Sonchus uliginosus, Sonchus arvensis variety uliginosus(Field Sow-thistle)
Asteraceae (Sunflower Family)

Moist meadows, disturbed sites, openings. Summer, fall.
Bolam Pass Road, west side, September 11, 2015

The seeds (red arrow) are just 2-3 mm long, flattened, and topped by scores of silky, pappus hairs.

Sonchus arvensis subspecies uliginosus

Sonchus arvensis subspecies uliginosusSynonyms: Sonchus uliginosus, Sonchus arvensis variety uliginosus(Field Sow-thistle)
Asteraceae (Sunflower Family)

Moist meadows, disturbed sites, openings. Summer, fall.
Bolam Pass Road, west side, September 11, 2015.

Leaves have prickly margins and are 2-15 inches long, up to 4 inches wide, deeply to shallowly cut, clasping the stem, and reduced in size upward.

Range map © John Kartesz,
Floristic Synthesis of North America

State Color Key

Species present in state and native
Species present in state and exotic
Species not present in state

County Color Key

Species present and not rare
Species present and rare
Species extirpated (historic)
Species extinct
Species noxious
Species exotic and present
Native species, but adventive in state
Eradicated
Questionable presence

Sonchus arvensis subspecies uliginosus

Range map for Sonchus arvensis subspecies uliginosus