Ambrosia psilostachya
is a widespread ragweed species. Leaves are pinnately dissected. Male flower umbels
hang along the top of the stem. Female flowers are inconspicuous and are located
in leaf axils. Ragweed pollen causes hay fever.
Compare to Ambrosia
trifida, which has broader leaves. A. trifida has a black rib
on the involucre of the male flower umbels.
Compare to Ambrosia
tomentosa, which has more finely dissected leaves. Female flower heads
are spiny burrs.
