Looking down from the Viewing Platform at Pelican Island National Wildlife on March 11, we saw a striking and substantially sized specimen of spiny sowthistle (Sonchus asper), an elongate pyramid thriving in the rich marshy soil. Spiny sowthistle can grow up to be 6 feet tall in fertile conditions.
This non-native weed of European origin also is known as spiny milk thistle, spiny milk thistle, sharp-fringed sow thistle, and prickly sow thistle. Milk thistle refers to the white latex held inside the hollow central stems.
The alternate leaves are toothed, prickly, curled, and rough (the species name asper means rough). Young, soft leaves were fed to lactating pigs, spawning many of the common names.
The leaves on the upper stem are dramatically reduced in size.
Flowering occurs in the winter, spring, and summer. Its yellow flowers are held in terminal corymbs and belie that it belongs to the daisy family, Asteraceae.
Its tiny seeds are attached to silken filaments and spread by the wind.
Spiny sowthistle is a weed of disturbed sites, old fields, and sometimes gardens. It occasionally volunteers along the trails at Oslo Riverfront Conservation and can vary greatly in size. Thick gloves are necessary if you wish to remove it.