Sunflower Seeds

Plant in summer or fall. Takes 8 days to produce a large sunflower. Yields more seeds at harvest.
Overview
Sunflower Seeds are a type of seed. When planted, they grow into Sunflowers, which also drop 0–2 Sunflower Seeds when harvested, making them a renewable crop-related item once Sunflowers are cultivated.
They can be purchased at 

Sunflower Seeds are not used in any recipes.
A notable quirk affects their sale price when stacked from different sources. When selling Sunflower Seeds to Stone, seeds harvested from Sunflowers or bought from Stone sell for 4g each. However, seeds purchased from JojaMart sell for 3g each. If a single JojaMart-bought seed is placed in a stack with harvested seeds, the entire stack sells for 3g each. If the purchased seed is instead added to a stack of harvested seeds, or seeds bought from Stone, the entire stack sells for 4g each. This makes the order in which stacks are combined important when selling mixed seeds.
Official description
Plant in summer or fall. Takes 8 days to produce a large sunflower. Yields more seeds at harvest.