Abstract
Seed germination is the most important transitional event between early stages in the life cycle of spermatophytes and understanding it is crucial to understand plant adaptation and evolution. However, so far seed germination of phylogenetically closely related species has been poorly investigated. To test the hypothises that phylogenetically related plant species have similar seed ecophysiological traits thereby reflecting certain habitat conditions as a result of local adaptation, we studied seed dormancy and germination in seven Mediterranean species in the genus Romulea (Iridaceae). Both the across‐species model and the model accounting for shared evolutionary history showed that cool temperatures (≤ 15°C) were the main factor that promoted seed germination. The absence of embryo growth before radicle emergence is consistent with a prompt germination response at cool temperatures. The range of temperature conditions for germination became wider after a period of warm stratification, denoting a weak primary dormancy. Altogether these results indicate that the studied species exhibit a Mediterranean germination syndrome, but with species‐specific germination requirements clustered in a way that follows the phylogenetic relatedness among those species. In addition, species with heavier seeds from humid habitats showed a wider range of conditions for germination at dispersal time than species from dry habitats possessing lighter seeds. We conclude that while phylogenetically related species showed very similar germination requirements, there are subtle ecologically meaningful differences, confirming the onset of adaptation to local ecological factors mediated by species relatedness.
Highlights
Knowledge of plant evolution and species delimitation may be limited by a lack of information on the reproductive biology of plant species and how it fits into their life cycles (Grant 1981; De Queiroz 2007; Stuessy 2009)
Ecology and Evolution published by John Wiley & Sons Ltd
(t50) revealed that k did not differ significantly from unity (k = 1, CI 0.86, 1), implying that the phenology of seed germination is more similar than expected from the phylogenetic relationships of the species
Summary
Knowledge of plant evolution and species delimitation may be limited by a lack of information on the reproductive biology of plant species and how it fits into their life cycles (Grant 1981; De Queiroz 2007; Stuessy 2009). Sexual reproduction and seed germination are two of the most important events in the life cycle of flowering plants. The timing of germination is affected by the environmental conditions which prevail during seed maturation and after seed dispersal. Germination is influenced by a large number of genes and environmental factors and is often mediated by seed dormancy (Koornneef et al 2002; Finch-Savage and Leubner-Metzger 2006; Bewley et al 2013). If a seed is dormant, certain environmental conditions are required to break its dormancy, while other environmental factors promote germination of seeds that have become nondormant. Seed dormancy is a quantitative trait of great adaptive importance, which evolved to cue emergence of seedlings at the environmentally most advantageous time a 2016 The Authors.
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