Xanthium strumarium

Fruiting Heads, Longitudinal Sections

Valeport Recreation Site, shore of Last Mountain Lake

Note the achene has been removed from the right-most chamber in Fruit B.

There are two types of flower heads.  Staminate flower heads contain a number of staminate florets, each consisting of a column of united filaments terminated by five distinct anthers.  Pistillate flower heads contain two pistillate florets surrounded by an involucre of persistent bracts with hooked tips.  Each ovary occupies one of two chambers in the interior of the involucre and each ovary is terminated by a two-branched style which protrudes beyond the involucre.  The involucre will eventually harden and become a burr which contains the two achenes.