Give me sources of citied for this idea"Plant Morphology**: Sunflowers are characterized by their tall, erect stems that can reach heights of 1.5 to 3 meters. The plant's leaves are large, broad, and rough in texture, with a rough surface that helps deter pests. Sunflowers produce a single large flower head per stem, composed of hundreds of individual flowers known as florets. The central disk flowers mature into seeds, while the outer ray flowers are ornamental."

Answer 1

1. "Gardening Know How: Sunflower Plant Care - Sunflower Varieties for Gardens" by Heather Rhoades, published on Gardening Know How website, accessed on March 2, 2022.
(https://www.gardeningknowhow.com/ornamental/flowers/sunflower/sunflower-plant-varieties.htm)

2. "The Plant List: Helianthus annuus L." by The Plant List, published on The Plant List website, accessed on March 2, 2022.
(https://www.theplantlist.org/tpl1.1/record/gcc-10727)

3. "University of Minnesota Extension: Sunflowers" by the University of Minnesota Extension, published on University of Minnesota Extension website, accessed on March 2, 2022.
(https://www.extension.umn.edu/garden/yard-garden/flowers/growing-sunflowers/)

4. "Missouri Botanical Garden: Helianthus annuus" by Missouri Botanical Garden, published on Missouri Botanical Garden website, accessed on March 2, 2022.
(https://www.missouribotanicalgarden.org/PlantFinder/Helianthus-annuus)