Serotiny in Primula palinuri: How to Face the Dry Season on Mediterranean Cliffs

Primula palinuri Petagna is the only Mediterranean and maritime species in the genus Primula, is endemic to coastal cliffs of southern Italy, and is classified as endangered with a decreasing population trend in the IUCN Red List. For this species, the major bottleneck for long-term survival has been recognized to be recruitment failure. In this study, we investigated the seed release strategy of P. palinuri, by using field observations and laboratory experiments. We hypothesized that repetitive cycles of wet/dry conditions and external wax removal could be the environmental triggers of capsule dehiscence. Data showed that capsules treated with wet/dry cycles dehisced within 75 days, while none subjected to constant dry conditions dehisced. Once dehisced, capsules repetitively closed when made wet, and opened again upon drying. Seeds of P. palinuri can remain on plant up to 2 years, over which time capsules reclose when rained upon and reopen upon drying, highlighting the first reported occurrence of serotiny in a Primula species. Serotiny allows P. palinuri to face the dry season, by avoiding capsule dehiscence during the summer dry period and delaying seed release until the beginning of fall, when water availability in the soil is generally no longer a limiting factor.