Ambrosia psilostachya

A comparatively broad-leaved Ambrosia with merely tuberculate (rather than spiny) fruits.

Plant habit in the floodplain of the Gila River near Mogollon Box, 23 Sep 2007.

Cauline leaves in the Gila River floodplain, 23 Sep 2007.

Inflorescences, Gila River floodplain, 23 Sep 2007. Staminate pseudanthia are readily visible, the pistillate pseudanthia are hidden in the axils of the upper leaves.

Staminate pseudanthia, Gila River floodplain, 23 Sep 2007.

Pistillate pseudanthia, Gila River floodplain, 23 Sep 2007.

Another pistillate pseudanthium, Gila River floodplain, 23 Sep 2007.

Plant habit, Gila River floodplain, 23 Sep 2007.