Xanthium strumarium

Pistillate Florets, Inner Sides

Valeport Recreation Site, shore of Last Mountain Lake

Two pistillate flower heads were split longitudinally to separate the two florets comprising each head.  This is a photo of the inner faces of two of these florets (one form each head).  The separation plane was further toward the viewer in Floret A than in Floret B.  Thus the ovary in Floret B is fully exposed, while the ovary in Floret A may actually be from the adjoining (removed) floret.

Note the proximal involucral bracts have hooked tips but there are a few horn-like distal bracts which are larger and have less hooked tips than the proximal ones.

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.