A Glowstem is a type of plant found in Pikmin 2 on the GameCube. It can be found in the underground segments of the game, where you'll find two different colors of it - red and green, though overall the difference in color makes no difference to the gameplay. The plant's top is bright, and will lighten up the underground areas. In the game, Captain Olimar notes the similarities between the Glowstem and the street lights found on his home planet, Hocotate.
A similar plant found in the game is the Common Glowcap, which resembles a mushroom.
"Although they are obviously unrelated, the glowstem bears a striking resemblance to the street lights on Hocotate. It is highly possible that glowstems could be a relic of some unknown civilization beyond the scope of our imagination."
"Inedible. Known effects include uncontrollable episodes of impromptu break dancing."