Ambrosia artemisiifolia (Common ragweed)
Image credit: Rodion KutsaevIdentification tips
Tip #1: to remember the scientific name, the name of the genus comes from the Greek "food of the gods", traditionally considers the food of the gods a dessert called ambrosia and I like to think that the goddess of hunting Artemis loved this dessert, so they named this species as ambrosia armesisiifolia. And why the "folia (leaf)" at the end? Just remember that the leaf of the plant resembles a hunting arrow.
Plant shape
2º Identification tip: the leaves are bluish-green and covered with fine hair. Split leaves and the lower sides covered with fine hair, giving a gray appearance.
Leaves
3º Identification tip: the leaves are the key to identification, they have a lacy appearance and spear shape, composed of several leaflets.
Stem
4º Identification tip: the stems can often have purple, reddish and brown coloring when more mature, usually new stems are green, it is not uncommon to see stems that the sun-facing face is reddish and the other is green, the stems are not hollow.
Flowers
5º Identification Tip: the flowers are practically unique, possessing very peculiar characteristics, reminiscent of a pot of ambrosia.
Seeds
6º Identification tip: the seeds have a straw, black and moss coloring, have a peculiar characteristic looking like a small head with a small crown and a pointed hat, care must be taken not to be confused with the seed of Ambrosia trifida, this one has the crown and hat much larger.
Seedlings - the terror of all
7º Identification tip: look for the lobed leaf (similar to lace or fern) and the cotyledons are spoon-shaped, being round different from the real leaves.
Extra references:
https://gobotany.nativeplanttrust.org/species/ambrosia/artemisiifolia/
https://herbarium.cfans.umn.edu/Detail.aspx?SpCode=162&LimitKeyword=