| Souliea vaginata, Actaea asiatica and Beesia calthifolia, three perennial herb, belong to tribe Cimicifugeae (Ranunculaceae). While similar in systematic position, the three species show very different floral traits. In this paper, we demonstrate the floral syndrome, breeding system and pollination characteristics in these three species to explore the interaction between pollinators and flowers, as well as the pollination adaptive strategies to their anthecological environment. The main results are as follows:1. Floral syndrome and flowering characteristicS. vaginata and A. asiatica are compressed racemose inflorescences. The inflorescence of B. calthifolia is a raceme with several umbellate cymes. All of the three are protogynous. The S. vaginata, with showy floral display and rich rewards (abundant pollens and nectar), is characteristic with entomophilous flower. The flowering period of it lasts about one month. The life span of one floret is approximately 5-7d. While A. asiatica is characteristic with self-pollination syndrome: relative short longevity of a single flower (3-5d), protogyny, low P/O value and inconspicuous petals without nectar secretion. All the floral traits indicate this plant is insufficient for long-range attraction in its pollination environment. A. asiatica finishes selfing by two ways:1) the upper part of the abscissing sepals cover stigma and partial stamens until the later period resulting in the deposition of self pollen on the stigma and causes autonomous self-pollination.2) The close proximity and concurrent development of anthers and stigmas among flowers within an inflorescence causes geitonogamy. It is likely that both ways could provide reproductive assurance for A. asiatica under conditions of pollinator scarcity. There is no petals and nectar secretion in B. calthifolia. The white petaloid sepals are responsible for pollinator attraction. The flowering period is quite extended from June to August.2. Types of breeding systemsS. vaginata and B. calthifolia are all protogynous with an out-crossing index of 4 bases. According to criterion of Dafni(1992), the breeding system is outcrossing with partial self-compatibility, needing pollinators. The P/O value of the both species, are 1665.40±309 and 1673.58±689.75 respectively. Based on Cruden's criterion(1977), the breeding system both are facultative xenogamy. Field experiments of S. vaginata indicate that this species is self-compatible. No apomixia and anemogamy seems to occur. Fruit set in the bagged flowers with anthers indicates the presence of autogamy, but the seed set of this treatment is significantly lower than that of open-pollinated flowers. This demonstrates that S. vaginata depends mainly on timely visiting of pollinators. It is likely that autogamy provides reproductive assurance for S. vaginata because of the ineffective pollinators. In the natural populations of A. asiatica pollinator visitation is rare. No apomixia and anemogamy exists. Both open-pollinated flowers and bagged flowers with anthers set abundant seeds, which demonstrate A. asiatica relies predominantly on selfing under natural conditions. Combing the relative low P/O value (771.46±213.98) and out-crossing index (3), we conclude that A. asiatica is a facultative selfer. This mating strategy, which related with the dense inflorescences, sepal abscissing, pollinator scarcity and low plant density, is common in genus Acteae, and could provide reproductive assurance for A. asiatica under conditions of pollinator scarcity.3. Pollination characteristicsThe most common floral visitors of S. vaginata are arranged in Homoptera(Aphididae), Hymenoptera(Braconidae), Diptera(Sciaridae) and Coleoptera(Chrysomelidae and Biphyllidae), such as the Myzus persicae Sulzer, Sitobion miscanth L. and a species of Braconidae that can not be identified exactly, as well as the mating and foraging beetles. From the observation by SEM, we find Myzus persicae Sulzer, Sitobion miscanth L and the insects of Braconidae take a lot of pollens on their bodies, while the beetles take a few pollens. Because of their low visiting frequency or poor pollen taken ability, all of the insects are not efficient pollinators, but the spontaneous autogamy remedies the insufficiency. During the long-term evolution, the floral traits of S. vaginata are closely associated with its pollinator adaptation:1) pollination by beetles is related to protogyny.2) The petals of S. vaginata not only serve as a cornucopia of nectar to the small visitors, but also offer comfortable rest sites to them.3) The flowering peak coincides with maximal colony size of the Myzus persicae Sulzer. The pollinator visitation of A. asiatica is rare. There is no efficient pollinator observed to visit the flower. The white petaloid sepals of B. calthifolia are conspicuous in natural population, and are responsible for pollinator attraction. Pollen is the only reward which B. calthifolia provides to the visitors, so the most common floral visitors are limited to one order, Diptera. The mainly pollinators are two species of Syrphidae and Conopidae respectively. Both of them are pollen collectors. They usually grasp the stamens and often touch the stigma with pollen-dusted parts of their bodies. Combining with the extremely high visiting frequency (10.67 times per hour and 13.00 times per hour, respectively), we can take them as the efficient pollinator to B. calthifolia despite their poor ability to carry pollen.In conclusion, the three species show different solutions to the problem of insufficient pollinator attraction, and to adapt to thier anthecological environment. S. vaginata, with nectar and aboundant stamens, attracts a broad spectrum of insects to service for it. Besides, the autogamy provides reproductive assurance for S. vaginata when the pollinators are unreliable. Facultative autogamy in the self-compatible A. asiatica seems to be evolved in response to very low pollinator density in the habitat. The B. calthifolia, with poor reward, attracts white preference flies to facilitate the cross pollination. |
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