The process of evolution works slightly differently in plants than animals. Differences in plant physiology and reproduction mean that while the same evolutionary principles of natural selection apply, the finer nuances of their effect are radically different.

One major difference is the ability of plants to reproduce clonally, and the totipotent nature of their cells, allowing them to reproduce asexually much more easily than most animals. They are also capable of polyploidy – where more than two chromosome sets are inherited from parents. This allows relatively fast bursts of evolution to occur. The long periods of dormancy that seed plants can employ also makes them less vulnerable to extinction, as they can “sit out” the tough periods and wait until more clement times to leap back to life.

The effect of these differences is most profoundly seen during extinction events. These events, which wiped out between 6 and 62% of terrestrial animal families, had “negligible” effect on plant families. However, the ecosystem structure is significantly rearranged, with the abundances and distributions of different groups of plants changing profoundly. These effects are perhaps due to the higher diversity within families, as extinction – which was common at the species level – was very selective. For example, wind-pollinated species survived better than insect-pollinated taxa, and specialised species generally lost out. In general, the surviving taxa were rare before the extinction, suggesting that they were generalists who were poor competitors when times were easy, but prospered when specialised groups went extinct and left ecological niches vacant.
Source: http://en.wikipedia.org/wiki/Evolution_of_plants

See Also: Bouquet, Roses, Floral