Evolutionary ecology of fast seed germination—A case study in Amaranthaceae/Chenopodiaceae

Germination is a vulnerable and risky step in a plant’s life cycle. Particularly under harsh environmental conditions, where time windows favourable for seedling establishment and survival are short or unpredictable, germination speed might play a highly adaptive role. We investigated the germination speed of 107 Amaranthaceae s.l. at two different temperatures and related the results to various plant and habitat traits taking into account the molecular phylogenetic relatedness of the species sampled. Germination speed is a fast evolving trait in Amaranthaceae s.l. It evolves towards significantly faster optima in C4 and halophyte lineages, albeit for different reasons. While C4 photosynthesis and fast germination are simply traits beneficial under the same environmental conditions, saline habitats, especially in subtropical regions, seem to select for fast germination. Heterospermy is probably much more common than currently known in Amaranthaceae s.l. and likely evolved as a bet-hedging strategy in lineages with fast seed germination. The evolution of germination speed is neither related to seed mass, an evolutionary stable trait, nor dependent on plant longevity and plant height. Correlation analyses of climate variables and germination speed suggest that there is an indirect effect of climate which is dependent on the ecological niche of the species.