Protandry, pollination, and self-incompatibility in Discaria toumatou

Abstract

Discaria toumatou (Rhamnaceae) is a spiny shrub endemic to New Zealand. The small white flowers are protandrous. Pollen is presented first and removed by wasps, flies, and bees which visit the flowers; after one to three days the three stylar branches unfold and an exudate is produced covering the stigmatic area at the tip of each branch. Pollen germinates only on the three restricted receptive areas. Controlled crosses on field plants and fluorescent microscopy confirm that D. toumatou is self-incompatible. The site of inhibition is at the stigma. The species provides a clear example of the co-occurrence of dichogamy and self-incompatibility, and has an unspecialised pollination system as is characteristic of many New Zealand plants.

Keywords:

• Discaria toumatou
• Rhamnaceae
• incompatibility
• protandry
• pollen-stigma interference
• stigmatic surface
• New Zealand