Why does the Kurinji plant flower only once in 12 years

Kurinji or Neelakurinji (Strobilanthes kunthiana), is a shrub that used to grow abundantly in the shola grasslands of the Western Ghats in South India above 1800 metres. The Nilgiri Hills, which literally means the blue mountains, got their name from the purplish blue flowers of Neelakurinji that blossoms gregariously only once in 12 years.Kurinji (Strobilanthes kunthiana) and a number of other plant species synchronise their flowering (reproductive phase) within large local populations at a particular site[1].

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[2].

Certain clumping bamboos also reproduce in this episodic manner. Once they flower they die. This can be hard on a gardener who has used bamboo as an element in their garden design. Historic mass flower and death in bamboo occurred in 919 & 1114 in China. In Japan it was 1716 & 1845 when the plants died. Since then the Fargesia bamboos have bee growing in Europe and America. In 1960’s stocks all over the world flowered and died. These plants have a about 120 year seed cycle.
Certain trees fruit this way, both Oak and Ash trees do. In fact the phenomena is called mast fruiting because nuts on the forest floor are called mast. This dates back to when swine ran free eating the mast in fall to be fattened before slaughter[3].


References


1.  Wikipedia.org, Strobilanthes kunthiana
2.  Hindu.com, http://www.hindu.com/seta/2006/06/15/stories/2006061500421700.htm
3. Answers.yahoo.com http://in.answers.yahoo.com/question/index?qid=20071015054616AAHJpHZ