Some species of liverworts have devised an interesting strategy. They explosively disperse their sperms into the air! Researchers in Japan recently published a research paper that includes documentation of the distance the airborne sperms disperse and a video of the dispersal. This phenomenon has been known to occur since the early 1900's, however little attention had been given to it. The stimulus that caused the dispersal was the addition of water to the plant. Thus the explosive dispersal would most likely occur during or after rainfall.
It quite the evolutionary solution! Rather than being limited by water and distance these plants have evolved a strategy to undergo sexual reproduction with greater success. If there is not a film of water uniting one plant with a mate, then they toss their sperm into the air after a little bit of rain and they might get lucky. Checkout the video below.
Shimamura, M., Yamaguchi, T. & Deguchi, H. 2008. Airborne sperm of Conocephalum conicum (Conocephalaceae). J. Plant Res. 121: 69-71.