Ambrosia is weeds disturbed in areas around Perth and occurring in temperate regions of the northern hemisphere and South America. It is very ordinary in appearance and is also called Ragweed.

Ambrosia is annual or perennial herbs. They have lobed or divided leaves ranging from small plants such as Ambrosia artemisiifolia (short or common ragweed) 30 cm to 1.5 m in height to A. trida, giant ragweed, which can reach 4 to 5 m tall.

The stems of Ambrosia are basally branched. They form a slender taproot or a creeping rhizome. The foliage is grayish to silvery green with bipinnatifid, deeply lobed leaves with winged petioles. But in the case of Ambrosia coronopifolia, the leaves are simple. The leaf arrangement is opposite at the base, but becomes alternate higher on the stem. The greenish yellow flower heads contain disc florets only, the male ones nodding in a terminal spike, the females upright, singly in the axils of the uppermost leaves. The numerous tiny male, yellowish-green disc flowers are about 3 mm in diameter. They grow in a terminal spike, subtended by joined bracts. The female, whitish-green flowers are 1-flowered and are inconspicuously situated below the male ones, in the leaf axils. The pappus is not there.

Ambrosia prefers dry, sunny grassy plains, and sandy soils. They grow well along river banks, along roadsides, disturbed soils, vacant lots and ruder sites.

Ambrosia artemisiifolia is a knee-high plant and is famous for causing sneezing fits, clogged sinuses and runny noses for folks with hay fever. Over 20 species of ragweed exist, but this one is probably the most common in the US and southern Canada.

Did you know?

·        Most allergy problems are caused by A. artemisiifolia and A. trifida, two species that account for more hay fever than all other plants together.

·        There are 41 species worldwide of Ambrosia.

·        The name of this genus is derived from the Greek word for "food of the gods".