Helianthus annuus (Common sunflower)
Image credit: Marko BlaževićIdentification tips
Tip #1: the genre comes from the ancient Greek helios, "sun" + ánthos, "flower". Annun means for one year, because of its an annual plant.
Plant shape
2º Identification tip: sunflower is an annual vigorous growing plant with a unique stem.
Leaves
3º Identification tip: the leaves have a rough texture and are oval or heart-shaped. The leaves are alternating and have hair. The top surface of the leaves is opaque green and covered with short, stiff hair, giving a sandpaper feel. Petioles are light green to reddish-green and covered with short, stiff hair; the top surface of each petiole is channeled.
Stem
4º Identification tip: the stem is light green and covered with white hairs, and may have a reddish color.
Flowers
5º Identification tip: the flowers are large yellow and a central disc red-brown. Flowers bloom between July and September. The flowers have bracts on the back, usually oval with a long, thin tip with stiff, short hair on the edges. A plant can have more than one flower, which appears on the side buds.
Seeds
6º Identification tip: the seeds have balloon shape and black coloration with white stripes.
Seedlings - the terror of all
7º Identification tip: seedlings are easy to identify because cotyledons are large and thick and oblong. The first true leaves have an oval shape.
References
https://www.minnesotawildflowers.info/flower/common-sunflower
https://www.wildflowers-and-weeds.com/Plant_Families/Asteraceae.htm