Biennial or sometimes perennial.
Stems (Fig 4,5) hollow, 1-5 cm in diameter, often hairy (a) below the nodes, often somewhat woolly or hairy throughout.
Basal leaves (Fig 6) long-stalked, 50-100 cm high, divided into 3 large, broad leaflets, these deep-lobed, sometimes the central one redivided, jagged-toothed with the veins mostly going to the tips of the teeth; stem leaves similar but smaller; lower portion of each leafstalk much expanded (b), almost balloon-like, circling the stem at the node (Fig 4).
Flowers (Fig 2,3) white in large, nearly flat-topped, compound umbels 10-20 cm or more across; seeds large, flat, elliptic in outline, 7-14 mm long. Flowers from June to September.
Cow parsnip occurs throughout Ontario in meadows and edges of moist woods.
It is distinguished by its large, broad trifoliate leaves, its slightly woolly or hairy stems (Fig 4,5), and its large, coarse umbels of white flowers (Fig 2,3).
Can cause phytophotodermatitis. http://www.weedinfo.ca/media/pdf/cow_parsnip_review.pdf to download a thorough review of this species.
Spotted water-hemlock (toxic), but usually Cow parsnip is much taller (103 m) and much coarser in general appearance.
Whole plant, roadside in Central Ontario, August.
Umbel of Cow parsnip.
White flowers in umbellettes of Cow parsnip umbel.
Hairy, wooly stem of cow parsnip.
Hairy stem of Cow parsnip.
Lower leaf of Cow parsnip.