Sunflowers are a popular annual garden plant because they grow quickly and have striking blooms. The cheerful, giant yellow flowers of a sunflower are easy to recognize, but the species Helianthus annuus has so many varieties that it's not always easy to identify it. Sunflowers come in a variety of colors and sizes, and they even can have differently shaped leaves. Fortunately there are some distinguishing features common to the whole species.
Pay attention to the growth of the plant. When a sunflower plant takes off in late spring, its daily growth is often noticeable, and some plants can grow a couple of inches in a day. Sunflowers generally start to bloom in late summer.
Feel the leaves of the plant. Sunflower leaves are almost always bristly or hairy feeling. Most sunflower leaves are large relative to the flower, but they can be heart-shaped, spike-shaped or oval. The leaves of sunflowers are usually dark green and they almost always have rough, serrated edges. A sunflower can often be identified by its leaves before it blooms.
Watch the flowers during the day. Sunflowers visibly turn their heads to face the sun as it moves across the sky, and they bow their heads as the sun goes down. This feature is particularly striking with with a whole field of sunflowers
Look at the blooms of the plant. Sunflower blooms can be many different colors, and there are even variegated varieties. What distinguishes sunflowers from other plants is that their blooms are actually made up of thousands of mini-flowers on the center disk. Each of these mini flowers produces one seed. Even the colored petals of a sunflower are mini flowers, called ray flowers.
Examine the mini flowers on the sunflower's disk with a magnifying glass. Each mini flower has five fused-together petals surrounding five stamens. The stamens are fused around a pistil, which holds a few stigmas that look like insect antennae.
Pull out a few seeds from the flower when it has finished blooming. Sunflower seeds are relatively large and easy to harvest. They are oval-shaped with one pointy end. The shells are white with light gray or brown lengthwise stripes. Crack open a shell to see the seed, which is usually flat and tan-colored. Its oval shape is also pointed on one end.
Taste a sunflower seed. The seeds are nutty-tasting with a slightly oily feel. Wildlife like squirrels and birds are attracted to sunflower seeds, and it can be a challenge to harvest any yourself before the animals get to them all.