 Estimates indicate as many as 2–4% of all flowering plants and 7% of all fern species are the results of polyploid hybridization.Many crop species such as wheat are hybrids, and hybridization is an important factor in speciation in some plant groups.Garden flowers in the genus "Saxifraga" are often hybrids, and a tetraploid natural hybrid, "Saxifraga osloenis", is thought to have formed at the end of the last ice age.. Homoploid speciation also occurs in plants, and has for example given rise to several species of sunflower.