Arrow-leaf Groundsel

Senecio triangularis

Species distinguishing characteristics: 

  • Leafy stems with triangular, coarse-toothed leaves
  • Large patches of tall plants in moist to wet soils
  • Open, branched clusters of yellow flower heads with 5-8 disorderly rays
  • Bracts below flower head are green with black tips and form a single row
  • Leaves largest near the middle of the stem

Family Characteristics: 

  • Multiple layers of bracts beneath the flowers
  • Flower heads composed of several smaller flowers; each smaller flower produces an individual seed
  • Flowers may contain disk florets, such as those in the yellow center of a daisy, and/or petal-like ray florets
  • Undivided leaves
  • Includes the food plants lettuce, artichoke, and endive

Growth habitat: 

Erect perennial, 0.3-1.5 m tall, with one to many stems, and a woody base.  Often grows in large patches from rhizomes.

Leaves and stems: 

Stems are smooth to sparsely hairy and unbranched.  Stems have alternate leaves, 4-20 cm long and 2-10 cm wide, with strongly coarse-toothed edges.  Leaves are largest near the middle of the stem and may become somewhat smaller (but not greatly reduced in size), narrower, and short-stalked to stalkless towards the top.  Triangular leaves (or somewhat heart-shaped) have broad, squared-off bases (more so on lower and middle stem leaves).  Leaves are hairless except for short hairs on veins closer to the ground.  Leaves may wither and drop by flowering time.

Flowers: 

Few to many yellow flower heads on sparsely hairy stalks in a short, flat-topped open cluster that is widely branched.  Flower heads, 0.8-2 cm across, are composed of about 5-8 disorderly petal-like ray flowers, 0.7-1.4 cm long, and a slightly domed center comprised of several disk flowers.  The involucral bracts forming a deep cup, 0.7-1.2 cm tall, are below the flower head and are green with black tips and tufts of glandular hair in a single row.

Roots: 

Fibrous roots or short rhizomes.

Seeds: 

Smooth, oblong achenes (hard-coated seeds), 2 mm long, with faint ribbing on the surface, and a tuft (pappus) of slender, white hair-like bristles at the tip.  

Habitat preferences: 

Moist to saturated, nitrogen-rich soils of open forests, meadows, thickets, avalanche slopes, and streambanks at mid- to subalpine elevations.  Prefers full to partial sunlight.

Interesting facts: 

The genus Senecio is large, and may contain more species than any genus in the plant kingdom.  Senecio is derived from the Latin senex, or “old man,” and refers to the white-bearded seeds. 

Arrow-leaf groundsel provides favorable forage for wild ungulates, especially elk and deer, and fair to good forage for livestock, such as sheep.  However, liver damage or vomiting may result if ingested in large quantities due to the pyrrolizidine alkaloids present in the plant.  These naturally occurring toxic compounds, which are most concentrated in flowers and seeds, are likely present in about 3% of the world’s flowering plants and are intended to deter predation by animals or insect.  Indeed, most grazing occurs before flowering.

Medicinally, arrow-leaf groundsel is a diuretic, an astringent, and a diaphoretic.  The Cheyenne Indians reportedly used tea made from the leaves or roots as a sedative for chest pain.

Biological Classification: