The adaptive biological reproductive response of the spurge Euphorbia pithyusa subsp. pithyusa on coastal and mountain bioclimates

Abstract

Plants of nine Euphorbia pithyusa subsp. pithyusa populations growing in Mallorca (Balearic Islands) under distinct bioclimatic conditions were chosen for the study, from coastal, with a semi-arid thermo-Mediterranean bioclimate, to mountain (1250 m), with both meso-Mediterranean and supra-Mediterranean bioclimate. The cyathia and fruits differed significantly in size between the populations, with the coastal populations producing smaller cyathia and fruits. Flowering and fruiting were prolonged and extended through different orders of the dichasia. However, the third-order dichasia produced, independently of the environmental conditions, the highest number of fruits of all the populations. Although seeds of all the populations showed comparable germination capacity at 20 °C, seeds from the highland populations were slower to germinate and exhibited prolonged dormancy, suggesting a direct relationship between the degree of dormancy and rainfall. These differences were significant (p ≤ 0.05) and independent of the yearly climatic variations for each of the populations studied. The reproductive strategies permitting E. pithyusa to have success in the colonization of zones with different bioclimates are based on possessing: a generalist pollination system and the capacity to adapt the length and intensity of the flowering and fruiting periods to climatic conditions and to vary the size and dormancy levels of seeds.

Keywords:

• Phenology
• seed set
• dormancy
• bioclimate adaptation
• Mediterranean plants

Acknowledgements

We are grateful to L. Cortés for his comments on the manuscript and information about the germination data of Euphorbia margalidiana and C. Ornée to improve the use of English in the manuscript.