Why this flowers only in 12 years?

Kurinji ( Strobilanthes sp.) and a number of other plant species synchronise their flowering (reproductive phase) within large local populations at a particular site. Populations at different sites may have different calendars, but the length of the cycle is almost the same within a particular species.This is one of the survival mechanisms evolved to escape complete destruction of the population by seed/flower predators and is termed `predator satiation'. Synchronisation of reproduction by large populations leads to an abundance of `prey' such that the predators are simply out-numbered.Therefore, the percentage of population destroyed by predators is significantly reduced. Jungle fowl and small mammals are the chief seed predators of Kurinji seeds. Other common examples of plants with synchronised flowering in long intervals include many species of bamboos, oaks and beeches. Predator satiation has been observed in a number of animal species such as the wildebeest of the Serengeti.

How do plants `count' the number of years?

They have an internal calendar, which recognises the difference in day length. There is very good evidence to show that by `recording' periodical changes in day length, these plants count the number of periods to wait before they flower. This calendar is usually well buffered for changes in environmental conditions and damages due to human activity such as burning. In addition, individuals that are `off-sync' will not survive due to predation. Each species waits for different periods of length before they flower so that they can accumulate enough nutrient reserves to produce a large number of seeds