arvense – field (Latin)

Native range: Europe and N Asia

Leaves:

• alternate
• lance-shaped
• irregularly lobed
• spiny-toothed
• hairless or green above
• densely white-hairy beneath

Flowers:

• dioecious
• male heads showier
• pink-purple, small heads of disk flowers only
• involcre (bracts near flower) 1-2 cm high
• bracts tipped with weak prickles
• several to many heads in an open inflorescence

Fruit:

• achenes (small, dry, one- seeded fruit)
• oblong
• flattened
• ribbed
• 3–4 mm long
• pappus of feathery, white bristles

Other characteristics:

• perennial from deep, wide-spreading roots and creeping rhizomes
• stems leafy, rather thin, green, without spiny wings, 30 cm to 2 m tall, highly branched above
• only thistle with male and female flowers on separate plants

Relevant info:

• bull thistle (C. vulgare) has much larger heads (involucres 2.5–4 cm high) and spiny-winged stems

Ecology & Adaptations:

• native to Eurasia
• found in fields, pastures, meadows, clearings, roadsides
• common and often abundant at low to middle elevations, primarily in settled or agricultural portions of PNW
• herbivore defense – spines
• vegetative reproduction:
  • spreads by rhizomes just beneath the soil surface
  • can also spread via root fragments
• seed dispersal – bristles attached to seeds facilitate dispersal by wind
• control:
  • combination of treatments is usually required
  • repeated digging at 7–28 day intervals for up to 4 years
  • repeated mowing to weaken stems and prevent seeding is effective in low-level infestations
  • various herbicides are recommended for agricultural settings (but not natural areas)