Sunflower
later in the season, and normally unbranched.
Sunflower leaves are phototropic and will follow the sun's rays with a lag of 120 behind
the sun's azimuth. This property has been shown to increase light interception and
possibly photosynthesis.
The sunflower head is not a single flower (as the name implies) but is made up of 1,000
to 2,000 individual flowers joined at a common receptacle. The flowers around the
circumference are ligulate ray flowers without stamens or pistils; the remaining flowers
are perfect flowers (with stamens and pistils). Anthesis (pollen shedding) begins at the
periphery and proceeds to the center of the head. Since many sunflower varieties have a
degree of self-incompatibility, pollen movement between plants by insects is important,
and bee colonies have generally increased yields.
In temperate regions, sunflower requires approximately 11 days from planting to
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