Abstract
Conopodium majus is a geophyte with pseudomonocotyly, distributed in Atlantic Europe. It is an indicator of two declining European habitats: ancient woodland understories and oligotrophic hay meadows. Attempts to reintroduce it by seed have been hindered by scarce seedling emergence and limited knowledge of its seed biology.Micro‐CT scanning was used to assess pseudomonocotyly. Embryo growth and germination were studied in the laboratory and the field, using dissection and image analysis. The effects of temperature, light, nitrate and GA3 on germination were tested. Seed desiccation tolerance was investigated by storage at different RHs and by drying seeds at different stages of embryo growth.Seeds possess morphological but not physiological dormancy. Embryo growth and germination were promoted by temperatures between 0 and 5 °C, arrested above 10 °C, and indifferent to alternating temperatures, light, nitrate and GA3. Pseudomonocotyly appears to result from cotyledon fusion. While seeds tolerated drying to 15% RH and storage for 1 year at 20 °C, viability was lost when storage was at 60% RH. Seeds imbibed at 5 °C for 84 days had significant internal embryo growth but were still able to tolerate drying to 15% RH.Reproduction by seed in C. majus follows a strategy shared by geophytes adapted to deciduous temperate forests. The evolution of fused cotyledons may enable the radicle and the hypocotyl to reach deeper into the soil where a tuber can develop. The embryo is capable of growth within the seed at low temperatures so that germination is timed for early spring.
Highlights
Temperate deciduous forests are characterized by a predictable seasonality
In some species with morphological dormancy (MD), embryo growth does not start until an additional physiological block is released, a trait known as morphophysiological dormancy (MPD), which has been suggested to be the ancestral character of all seed plants (Willis et al 2014)
We investigated the seed ecology of C. majus with the aim of revealing the seed internal morphology, the environmental control of embryo growth and germination, and the storage behaviour and desiccation tolerance of the seeds at different stages of embryo growth
Summary
Temperate deciduous forests are characterized by a predictable seasonality. During the growing season, the tree canopy closes and limits the amount of light that reaches the understorey. Embryo growth within the seed can delay germination until the end of a long and predictable unfavourable season, such as the period of canopy closure. For this reason, embryo growth may require months of exposure to temperatures characteristic of that season. MD occurs in 96% of Apiaceae species and most have a combined MPD (Willis et al 2014) Embryo traits in this family have been related to habitat preferences, with species adapted to shady habitats having smaller embryos that require cold temperatures for growth (Vandelook et al 2012)
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