Montana Field Guide

Taprooted annual. Stems erect, 25–90 cm tall, simple or branched. Leaves oblong to oblanceolate, pinnately toothed or lobed less than halfway to the midvein, 5–20 cm long, winged-petiolate below, auriculate-clasping above. Involucres 8–14 mm high; phyllaries glabrous. Ray ligules 3–5 mm long, inconspicuous. Achenes tan to red-brown, 2–3 mm long, smooth between the ribs (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

In Montana there are three Sonchus species – all yellow flowered and similar in form until you look closely.

Spiny-leaf Sowthistle – Sonchus asper, non-native, undesirable
* Plants: Annual (maybe biennial). Short taproot. Lacking rhizomes
* Flower Heads: Usually less than 2.5 cm wide (full flower). Yellow ligules 3-6 mm long, shorter than the tube portion of the ray floret. Involucre 8-15 mm tall.
* Achene: Strongly compressed and somewhat winged. Smooth between the 3 ribs on each side.
* Leaves: spiny- to prickly-toothed margins. Leaf base auricles often rounded and coiled against the stem.

Field Sowthistle – Sonchus arvensis, non-native, undesirable
* Plants: Perennial. Long-taproot with spreading rhizomes.
* Flower Heads: Usually 3-5 cm wide (full flower). Yellow ligules 7-13 mm long, more or less equal to the length of the tube portion of the floret. Involucre 10-20 mm tall.
* Achene: Bumpy on and between the 5 or more ribs.
* Leaves: Toothed. Leaf base auricles often rounded, straight or curved.

Common Sowthistle – Sonchus oleraceus, non-native, undesirable
* Plants: Annual (maybe biennial). Short taproot. Lacking rhizomes.
* Flower Heads: Usually less than 2.5 cm wide (full flower). Yellow ligules 3-6 mm long, shorter or longer than the tube portion of ray floret. Involucre 8-15 mm tall.
* Achene: Weakly compressed. Bumpy between the 2-4 ribs on each side. Also bumpy on the ribs.
* Leaves: Leaf base auricles with acute lobes and not coiled around stem.

Disturbed soil of roadsides, pastures, lawns, streambanks; plains, valleys (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

POLLINATORS
The following animal species have been reported as pollinators of this plant species or its genus where their geographic ranges overlap: Bombus vagans, Bombus bifarius, Bombus fervidus, and Bombus terricola (Thorp et al. 1983, Colla and Dumesh 2010).