Pollination ecology of Chloranthus serratus (Thunb.) Roem. et Schult. and Ch. fortunei (A. Gray) Solms-Laub. (Chloranthaceae)

Abstract

Flowering and pollination biology of Chloranthus serratus and Chloranthus fortunei were studied. Flowering took place from early March to mid-April in Ch. fortunei, and from April to September, the whole growth period, in Ch. serratus. The flowering period of an inflorescence of Ch. serratus averaged about 8 d and anthesis of a single flower was 5-6 d. Flowers are slightly protogynous. The flower emitted fragrance when the androecium became white. Both species are entomophilous with thrips as exclusive pollinators. Under natural conditions, fruit set occurs mainly as a result of cross-pollination, but self-pollination and agamospermy may occur in some cases. In flowers of Ch. fortunei and Ch. serratus, the incurved androecium, the carpel and the spike axis form a nearly closed chamber that contains the anthers and stigma. The development of a floral-axial chamber may be an important step towards a more economical and effective pollination system. Floral morphology, pollination biology and fossil evidence suggest that the main evolutionary trend in the genus Chloranthus is towards development of 'closed' flowers. The fidelity of the relationship between Chloranthus and thrips is regarded as a specialized feature of pollination biology and this relationship may have originated early in the evolutionary lineage.