ironweed
/ˈʌɪənwiːd/noun
Any of various plants growing as weeds of cultivated land and typically having tough or wiry stems; specifically (a) black or common knapweed, Centaurea nigra (now rare ); (b) North American any of several species of the genus Vernonia (family Asteraceae (Compositae)).
Origin
Early 19th century; earliest use found in Thomas Batchelor (1775–1838), farmer and writer on language. From iron + weed.