Final answer:
The Helianthus annuus, which can grow a head over 30 inches in diameter, is known as the sunflower, a tall plant with a woody stem and singular large head capable of photosynthesis using the C3 pathway.
Step-by-step explanation:
The plant with the scientific name Helianthus annuus, which can have a head growing to more than 30 inches in diameter, is commonly known as the sunflower. This plant is an annual herbaceous plant that usually has a single stem towering over two meters in height, with a large single head that may weigh up to two kilograms. The strength of the sunflower stem comes from a ring of vascular bundles, making it capable of supporting the heavy head. The sunflower is a photosynthetic autotroph that uses the C3 pathway, and it converts sugars to fats, which are present in the seeds.