Pop Green are the seeds of hostile plants found in the forest of "Greenstone" on Boin Archipelago. They can grow from seeds to full-sized plants in moments.
Heracles used these seeds as bullets, weapons, and tools. According to him, they have various uses, and he taught Usopp how they work.
Pop Greens are seeds with instant growth capabilities, being able to sprout into full grown plants in a matter of moments. Presumably native to the Greenstone forest in the Boin Archipelago, they have been effectively weaponized by Heracles (who is shown simply throwing them) and Usopp (who fires them using Black Kabuto). How they are triggered is currently unknown, but different seeds are known to act on different stimuli.
Some grow upon impact, others grow in the presence of an oncoming target, while others are capable of growing in mid-air. These seeds also have varying ranges and effects, even those not normally attributed to plants, such as one capable of piercing opponents, another being able to explode, while another is shown to release a shock wave. Each type of seed also has a different color scheme, which the user can use to tell what each one is capable of.
When Usopp upgraded Nami's Sorcery Clima-Tact, he added the growth abilities of the Pop Green in as well, where similar to his Black Kabuto, he gave Nami the ability to extend the size of her new staff.
Further Information: Usopp's Arsenal/Black Kabuto
After two years of training with Heracles, Usopp gained mastery of the Pop Green as a new type of powerful weapon. According to Heracles, these seeds have various uses, especially in combat. It should be noted that the names given are not confirmed to be the plants actual name, rather the name Usopp has given to each attack.
- Usopp has a flowerbed called "Usopp Garden" on the Thousand Sunny where he mass produces the Pop Greens so that he will never run out on them.