Sunflowers are large, rough, hairy broadleaf plants with large yellow flower clusters. They may be summer annuals or perennials. When mature, the center or disk flowers hold scores of seeds that are very attractive to birds. Eleven species of Helianthus are found in California and some are classified as noxious.
Seedling
Cotyledons (seed leaves) are bright green and two to three times longer than they are wide.
Mature Plant
Stems are single or branched depending on the species. They are thick and covered with coarse hair. Leaves are spade shaped and range from about 3 to 6 inches (8–15 cm) to nearly 1 foot (30 cm) across and generally have rough hairs.
Flowers
Flower clusters are composed of a dark center (disk flowers) surrounded by a halo of yellow to orange flowers that look like petals (ray flowers).
Fruits
Fruits are single-seeded (achenes) and resemble those of commercial sunflower seeds.
Reproduction
In some species propagation is by seed only and in other species, by seed and creeping roots.
