Synchronic blooming of many individuals
of the cactus Rebutia heliosa

Many plant species need pollinators in order to cross-pollinate and produce seeds; for this reason the production of flowers in various plant  is relatively synchronized and all mature individuals of the same species bloom at the same time, in spite of the variations in environmental conditions across a region. While such synchrony could be generated by responses to weather factors, it may represent an evolved response to optimize reproductive success.

Synchronous flowering of a species across a region may enhance fertilization and seed set during years with strong flowering responses as a higher concentration of flowers increases the probability of pollination. In addition, synchronous flowering may reduce the proportion of seeds attacked by seed predators due to predator satiation The resulting pattern is selectively advantageous in reducing the proportion of seeds lost to predators
 

Furthermore some plants belonging to different species living in the same area may simultaneously  presents similar typical adaptations for a very low pollination probability environment converging into parallel phenological patterns and synchronizes their blooming cycles so to maximize the attraction of pollinator

For example some cactus species  bloom only once a year  (or in a few cycling phases) and flowers last only one or a few days, so blooming tends to be massively synchronous with most stems in a population producing a flowers on a given day.
An other example are spring ephemerals and bulbous plant (e.g.:  hyacinths, and narcissi) that also all flowering simultaneously.