MORPHOLOGY

An erect, often unbranched, fast-growing, annual plant. Stems 0,7-3,5 m tall, hirsute. Leaves alternate, ovate, long-petroled, lamina with 3 main veins, 10-30 cm long, 5-20 cm wide, lower leaves opposite and cordate. Flowering head terminal on main stem, 10-40 cm in diameter, rotating to face the sun, sometimes drooping, heads on lateral branches smaller.Sunflower has not a single flower, but there are many small flowers packed together in a structure known as a head. On the outside of the head is a series of greenish bracts (little leaves). Next to the bracts are found the ray flowers, usually yellow. The ray flowers are sterile, their function is to attract insects. The flowers in the center of the head, called disk flowers, are smaller and quite different in shape and color

 

Disk flower consists of a tubular five-lobed corolla which represents five fused petals. Below the corolla is the inferior ovary. On either side on the top of the ovary are two small structures, technically known as the pappi. In many composites the pappi provide for efficient dispersal of the fruit. In the sunflower the pappus has no apparent function and falls off as the fruit matures. The disk flowers are perfect, spirally arranged on the head. The disk flowers are cross - pollinated, well adapted to pollination by insects. Commercial sunflowers (hybrids) have flowers that are self-compatible for pollination, meaning they do not require a pollinating insect. Hybrids replaced open-pollinated varieties because of their increased yield, pest resistance, uniformity, stalk quality and selfcompatibility.

 

 

The fruit is an achene, variable in size, usually from 1-1,5 cm long, full-colored or striped. Basic chemical composition and structure of achene is shown in figure No. 3.

 

 

 

Achene of sunflower:
Taproot strong, penetrating to depth of 3 m and with large lateral spread of surface roots. Root system is highly efficient, so it can utilize nitrogen and moisture from lower soil levels and thus can be grown in areas which are too dry for many crops. Plants are quite drought - resistant except during flowering. Sunflower has quite short growing season, generally requiring 100-150 days from planting to maturity, depending on hybrid, cultivar and use (seed production, silage). The crop may be grown on a wide range of soils, including poor, provided they are deep and well-drained, but the plants don´t like acidic or waterlogged soils. The high stalks remaining after-harvest can make excellent snow traps.