The glowcap family is a family of fungi found in the three main Pikmin games, as well as Pikmin Adventure. Both variants shed light and are found only underground. In Pikmin and Pikmin 2, they are only cosmetic, like most plants. However, in Pikmin 3, the Common Glowcap can be used as shelter from the Vehemoth Phosbat and can be used for light. This type of glowcap is also used in Pikmin Adventure to breifly light up cave sections, which is what happens when touched.
Rather than actual plants, Glowstems are LEDs (light emitting diodes) with either a green or orange light. If touched, the light will flicker for a moment, and then return to normal. They are found in caves with metallic scenery.