Embryo morphology indicates physiological maturity better than seed mass in Syngonanthus elegans (Eriocaulaceae)

Syngonanthus elegans is used for dried flower arrangements and is one of the most important economic species in the family Eriocaulaceae. Due to over-collection, this species and congeners have become threatened with extinction in their natural environment. Variable germination has been observed for this species. A better understanding of germination problems may assist in the development of cultivation methods, thereby reducing the pressure on natural populations and safeguarding their survival. Seeds harvested from a natural population were sorted by testa colour into four groups ranging from dark red to pale brown. Seeds were then subjected to digital X-ray imaging and germination tests. X-ray images showed differences in the embryo size for the four colour fractions, indicating a difference in maturity that was confirmed by seed mass. The fraction with the smallest embryos also displayed the lowest viability. However, embryo size and seed mass showed a poor linear relationship. A strong association was observed for germination capacity and embryo size, but a weaker association for germination capacity and seed mass. Fluridone increased germination in the most mature fraction, but not in the other three fractions. We conclude that during seed development, maximum germination capacity is reached prior to mass maturity and that physiological dormancy develops late during maturation.