Trop picks: Impatiens

The Indian subcontinent is home to over two hundred species of impatiens, with two centres of biodiversity, in the Eastern Himalayas and the Western Ghats.

The endangered Impatiens scapiflora grows on the wet rocks of the Ghats' rainforests and was initially identified by Benjamin Heyne, who was the first European to be put in charge of the botanical gardens at Lalbagh after the fall of Mysore to the British. Heyne's instincts were confirmed by the great William Roxborough of the Calcutta botanical gardens. 

Impatiens are worth your attention for a plethora of reasons (not least because some species contain the compound napthoquinone, which is a key ingredient in Preparation H). But the one I want to talk about here is that impatiens can recognize each other through what is called "kin recognition."

Impatiens typically grow in the understory of rainforests, where competition for light is fierce. When an impatiens finds itself growing next to a non-impatiens, it increases its resource allocation to its leaves. As a result, its leaves become bigger and crowd out/ cast shade on its competitor, thus giving the impatiens an edge.

When an impatiens finds itself growing next to a kinsman/ kinswoman, however, its behaviour changes to become more altruistic. Instead of shading the other plant, the impatiens elongates and branches out, so that both plants can share what little light is available.

Scientists haven't yet figured out the mechanics of kin recognition, but they have observed that it only happens when two or more impatiens are root neighbours.

Their ability to recognize kin makes even more sense when we consider the way impatiens propagate, i.e. impatiently, through swift seed dispersal even when the slightest pressure is exerted on the seed pods. The seeds land close to the mother plant, thereby creating clusters of closely related individuals, who co-operate, rather than compete, to ensure their survival.