Physicists Philippe Marmottant and his team have observed a unique form of locotion in the spores of the Horsetail (Equisetum) plant. Each spore (measuring ~50 micrometers) is equipped with four appendages (elaters) that "are initially wrapped around the main spore body, and that deploy upon drying or fold back in humid air." Changes in humidity alter the shape of the appendages allowing it to 'crawl' in a random direction. However, a spore can explosively propel itself if the elaters are initially tightly bundled and subsequently unfurled through a change in humidity.
The researchers speculate that "the study will inspire new biomimetic classes of self-propelled objects, based on many appendices that open/close and that undergo friction with the ground."
As an aside, this pattern of behaviour is fairly reminiscent of the shape retaining properties of memory allow/polymers.