Horsetail
Equestrius vindico, this is not the scientific name given by humans.
The Horsetail is a brown plant, that easily sticks out of the ground like a post. It is a hardy plant that can survive when its supply of nourishment is very low in variety and quality, thus making it seen more often in rather shady places, such as caves. This plant reproducts by the release of spores. This plant, like most others, has no help to you and the Pikmin.
Olimar's Notes
This variety of horsetail is prevalent in regions with low nutrient content in the soil. Unlike most other plants, this particular species propagates itself through the release of spores.