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

## TL;DR

This study shows that some Argyreia plant species evolved from producing dormant seeds to non-dormant seeds, adapting to their wet habitats.

## Contribution

The paper provides evidence of an evolutionary reversal from physical dormancy to non-dormancy in Argyreia seeds.

## Key findings

- Three Argyreia species have non-dormant seeds, while two retain physical dormancy.
- Non-dormant seeds are found in species with restricted geographic distribution.
- Anatomical remnants suggest non-dormant seeds evolved from physically dormant ones.

## Abstract

Argyreia 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 Argyreia 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 A. kleiniana, A. hirsuta and A. zeylanica imbibed water and germinated to a high percentage, but only scarified seeds of A. nervosa and A. osyrensis 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 A. kleiniana, A. hirsuta and A. zeylanica seeds survived desiccation to 10% moisture content (MC) and >90% of A. nervosa and A. osyrensis seeds with a dispersal MC of ~12% were viable, seeds of the five species were desiccation-tolerant. A. nervosa and A. osyrensis have a wide geographical distribution and PY, while A. kleiniana, A. hirsuta and A. zeylanica have a restricted distribution and ND. Although seeds of A. kleiniana are ND, their seed coat anatomy is similar to that of A. osyrensis with PY. These observations suggest that the ND of A. kleiniana, A. hirsuta and A. zeylanica 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.

In Argyreia , the most recently split-off genus of the Convolvulaceae, some species produce seeds with physical dormancy, and some produce non-dormant seeds. Species with a wide distribution have seeds with physical dormancy, while those with a restricted distribution have seeds with no dormancy. Moreover, species that split-off early have seeds with physical dormancy. Physical dormancy is the ancestral dormancy class of the genus, since its sister groups only contain species that produce physically dormant seeds. Seeds of the species with non-dormant seeds have remnants of anatomical and morphological structures of seeds with physical dormancy. The evidence suggests that non-dormant seeds are an adaptation and reversal of physical dormancy in Argyreia , and species with non-dormant seeds split-off recently and have a restricted distribution.