Evolutionary reversal of physical dormancy to nondormancy: evidence from comparative seed morphoanatomy of species (Convolvulaceae).

is the most recently evolved genus in the Convolvulaceae, and available information suggests that most species in this family produce seeds with physical dormancy (PY). Our aim was to understand the evolution of seed dormancy in this family via an investigation of dormancy, storage behaviour, morphology and anatomy of seeds of five species from Sri Lanka. Imbibition, germination and dye tracking of fresh intact and manually scarified seeds were studied. Scanning electron micrographs and hand sections of the hilar area and the seed coat away from the hilar area were compared. Scarified and intact seeds of , and imbibed water and germinated to a high percentage, but only scarified seeds of and did so. Thus, seeds of the three former species are non-dormant (ND), while those of the latter two have physical dormancy (PY); this result was confirmed by dye-tracking experiments. Since >90% of and seeds survived desiccation to 10% moisture content (MC) and >90% of and seeds with a dispersal MC of ~12% were viable, seeds of the five species were desiccation-tolerant. and have a wide geographical distribution and PY, while , and have a restricted distribution and ND. Although seeds of are ND, their seed coat anatomy is similar to that of with PY. These observations suggest that the ND of , and seeds is the result of an evolutionary reversal from PY and that ND may be an adaptation of these species to the environmental conditions of their wet aseasonal habitats.