Tristyly

This type of floral mechanism is thought to encourage outcross pollen transfer and is usually associated with heteromorphic self-incompatibility to reduce inbreeding.

For example, in the short-styled morph, the two sets of stamen are arranged in the mid and long position in order to prevent autogamy.

In trimorphic incompatibility system, full seed set is accomplished only with pollination of stigmas by pollen from anthers of the same height.

[3] Tristylous species have been found in several angiosperm families including the Oxalidaceae, Pontederiaceae, Amaryllidaceae, Connaraceae, Linaceae and Lythraceae, though several others have been proposed.

[7] The rarity and complexity of tristyly coupled with its development in a variety of unrelated plant families has made its evolution and adaptive significant hard to discern.

[3] The adaption for structural variation in heterostylous species likely developed out of the need for efficient pollen transfer and simultaneous selection to reduce self-fertilization.