The common sunflower (Helianthus annuus) is an annual that can reach towering heights of up to 10 feet. There is more intrigue to this plant than just its height, however. The many uses and characteristics of the various plant parts make it an appealing addition to any garden or landscape.
The support system for a sunflower lies in the roots and stalk of the plant. Sunflowers have a taproot that is strong and can break through hard soil, providing the tall plant a much-needed anchor. Roots are also responsible for absorbing water and minerals, which are sent up through the stalk to the rest of the plant. The sturdy stalk provides the stability the large flower head needs to remain upright and a structure to house the leaves. Within the stalk is a system of channels that transport water, minerals and sugars throughout the plant. Dried stalks can be used for livestock feed once the blooms have finished their show.
Leaves and Buds
Large, green leaves grow out of the sunflower stock and are responsible for the majority of the energy-producing photosynthesis for the plant. The leaf blade is the flattened area and contains small hairs. The petiole is the thin stemlike piece that attaches the leaf to the stalk. On the common annual sunflower, a bud develops at the end of the stalk and turns to face the sun throughout the day. Once the flower opens, this repositioning stops and the flowers remain open to the east.
Sunflowers are known as composite flowers. The large flower head at the top of the stalk is often referred to as one flower but is actually hundreds of small flowers. The dark center is made up of disk flowers that have five brown petals fused together into a tubular shape. The male, stamen, and female, stigma, are both present in disk flowers. The stamen is composed of filament and pollen-producing anthers. The stigma houses the style, which receives the pollen and allows it to travel down to the ovary, where the unfertilized seeds, ovules, are located. This is the process of pollination that enables the flowers to produce seeds. Sunflower seeds are a common snack for humans and wildlife. Seeds can be saved and planted the following year to grow a new crop of sunflowers.
The outer circle of the sunflower head -- typically yellow -- is mistakenly referenced as the petals of the flower. In fact, these yellow pieces are individual ray flowers. They do not have reproductive parts and consequently will not produce seeds. Ray flowers are more essential in their role of attracting pollinators to the disk flowers and providing the aesthetic appeal of the plant.