Giant Ragweed
Scientific Name: Ambrosia trifida L.
Other Names: Iron-weed, great ragweed, wild hemp, horse-weed, and bitterweed..
Life Cycle: summer annual
General Description: Erect, tall plant with large distictively three-lobed leaves.
Seedlings: Cotyledons
are round, oblong, and thick (3-5x larger than common ragweed). Young
leaves are opposite and covered in rough hairs. First pair of leaves are
unlobed, but have large teeth on the margins (possibly small lobes).
True Leaves and Stem: Stems
and leaves are rough and hairy. Leaves are opposite and divided into
three lobes. Lower leaves are more deeply lobed that upper leaves.
Petioles are winged on the margins.
Roots: Primarily fiberous, but shallow taproot may be present.
Flower and Fruit: Flowers
produce large amounts of pollen. Flowers are small, green,
inconspicuous, and found on the ends of branches. Fruits have several
longitudinal ridges ending in 5 short spines (cimilar to a crown). Seeds
are approximately 6-12mm long (2x the size of common ragweed seeds).
Other Information: Pollen is the main cause of hay fever.