The Blastcap is a mushroom-like plant which is native to the planet Tallon IV. They can be found in the Tallon Overworld and Chozo Ruins areas. They resemble large capped mushrooms and they come in small and large sizes and also live in groups.
The spores of the Blastcap can survive in outer space, and have propagated throughout the galaxy by means of traveling on interstellar solar winds. When approached, they will make a rustling noise and shake violently. Upon contact with Samus, or when sufficiently damaged, they will explode. The explosion will damage Samus as well as release a cloud of gas as the mushroom itself is consumed. This can also often set off other nearby Blastcaps in a chain reaction effect. Contrary to its scan data, the gas is not harmful.
Blastcaps are also encountered in Metroid Prime Hunters on both Alinos and Arcterra. The gas emitted by this variant can harm Samus. The type that appears on Arcterra seems to be a white arctic species, though they appear to be merely scenery and cannot be scanned.
"Volatile chemicals within this weed's toxic fungal cap may explode if agitated. The poisonous flesh of the Blastcap helps keep it from being eaten. It also detonates its fungal cap when it senses even slight contact."
Metroid Prime Hunters
"A large mushroom that explodes on contact, emitting noxious gas. Originating on TALLON IV, its spores can survive without atmosphere and have propagated throughout the galaxy on solar winds."
- A similar species of mushroom known as "Blaxcaps" appears in the first Pikmin game during the final battle with Bulblax.