Flowering Frequency and Plant Performance and their Relation to Age in the Perennial Orchid Spiranthes spiralis (L.) Chevall.


Department of Plant Ecology Utrecht University P. O. Box 800.84 3508 TB Utrecht The Netherlands E-mail: J.H.Willems@bio.uu.nl


Abstract: Long-term demographic data have been analyzed to establish possible costs of flowering in the terrestrial orchid Spiranthes spiralis (L.) Chevall. in The Netherlands. Costs of flowering can be expressed as individual plant performance and flowering frequency in relation to the generative or vegetative status in the following year. Flowering in individuals of S. spiralis in a given year (t) is followed by a non-flowering phase in the next growing season (t + 1) in more than 80 % of the plants. The decline in flowering frequency is not a result of the age structure of the population involved because individual plants do not show signs of senescence after 10 - 15 years of aerial presence as an autotrophic plant. Rosettes have a smaller leaf area in the year of flowering (t), compared to the previous (t - 1) and following year (t + 1), due to the allocation of the limited underground resources to both flowering stalk and rosette at the beginning of its growing season. Generative reproduction in S. spiralis has a significant negative impact on both flowering frequency in subsequent years and on rosette size in the year of flowering. The flowering frequency and rosette size in relation to the life history, characterized by the yearly replacement of the underground tuber, is discussed. Better understanding of the life-history strategy, including costs of reproduction, may contribute to the creation of sustainable environmental conditions for growth of S. spiralis, e.g., optimal conditions for photosynthesis during the aboveground stage of the tiny wintergreen rosettes.