Facultative Self-pollination in Island Irises

Abstract

-Blue flag (Irzs versicolor) is an insect-pollinated clonal plant found in wet habitats throughout northeastern North America. Our study of an isolated population on Kent Island, New Brunswick, showed that blue flag was self-compatible. Moreover, we found no evidence of inbreeding depression. Although individual flowers were protandrous, the timing of male and female phases and the precise behavior of flowers depended upon whether the flowers had been pollinated. Naturally pollinated or hand-pollinated flowers closed their stigmas shortly after pollination, making them no longer receptive. Flowers from which pollinators had been excluded prolonged the period during which stigmas were open and reflexed downwards, increasing the likelihood that they could come into contact with their own anthers or petals onto which pollen had fallen. In the absence of insects, plants growing in exposed habitats apparently took advantage of wind to achieve pollination. Hand-pollination experiments showed no evidence of inbreeding depression. Fruit set, capsule size and the number of seeds per capsule did not depend on whether pollen came from the same flower, the same clone, the same population or different populations. Facultative autonomous self-pollination may be advantageous whenever pollination and outcrossing are unlikely, as in inbred populations, in small or clonal populations, or in populations where insect pollinators are scarce, ineffective or constrained by harsh environmental conditions.