General: Low-growing vine-like plant with hard, spiked seeds that can puncture tires.
Height: Usually grows along the ground but can grow upward if trying to access light.
Flowers: Yellow flowers with 5 petals. Flowers open in the morning only.
Leaves/Stems: Leaves are oval and 5-15 mm long arranged oppositely along the stem. Stems branch and spread up to 100 cm wide.
Root: Shallow taproot.
Goat’s-head, Bullhead, Caltrop, Tackweed
Not many look alikes but could be confused with other plants that are ground creepers forming mats. Prostrate knotweed (Polygonum aviculare), Prostate spurge (Euphorbia maculata), Common Silverweed (Potentilla anserina).
Where did it come from? Introduced from Eurasia.
Where does it grow here? Thrives in dry grassland, fields and disturbed areas. It has been spreading in the vineyards of the Okanagan. It can tolerate a wide range of soil conditions.
Reproduction: Grows by seed only. The fruit is spiny with 5 sections that split open when it matures. Each bur has 2 spines each with 2-5 seeds. The seed can stay viable in the soil for up to 5 years. One plant can produce up to 1 million seeds.
When does it grow, flower & seed? Sprouts May and throughout season until October. Flowers 3 weeks after first growth. Seeds 1-2 weeks after flowers.
Spreads By: The spines are very sharp which cause them to stick to shoes, tires, animals and wine grape containers.
Plant Type: Annual.
Okanagan Invasive Species Online website
E-Flora BC: Electronic Atlas of the Flora of British Columbia