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 Kuro 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 Kuro Kabuto, he gave Nami the ability to extend the size of her new staff.
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 plant's actual name, but rather the name Usopp has given to each attack.
Midori Boshi: Devil.
Midori Boshi: Sargasso.
Midori Boshi: Rafflesia.
Midori Boshi: Take Jave Rin.
Midori Boshi: Dokuro Bakuhatsu So.
Midori Boshi: Humandrake.
Midori Boshi: Trampolia.
Midori Boshi: Impact Wolf.
Midori Boshi: Boaty Banana.
Midori Boshi: Uchiwa Grass.
Grow Up Kuro Kabuto:Bakun So.
Super Grow Up Kuro Kabuto.
Midori Boshi: Platanus Shuriken.
Midori Boshi: Nemurisu.
Midori Boshi: Sea Devil.
Midori Boshi: Hebi Hanabi.
In SBS Volume 68, it was explained how 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 of them. This was also shown in Film Z, where he sprays insecticide on the flower bed.
Usopp Garden where he mass produces his pop greens.