Flowering dynamics in Arum italicum (Araceae): Relative role of inflorescence traits, flowering synchrony, and pollination context on fruit initiation

We studied the relative role of inflorescence traits, flowering synchrony, and pollination context for infructescence and fruit initiation in two Span ish populations of Arum italicum, a species in which inflorescences are the pollination unit. In this species. a specialized inflorescence organ. the appendix, is important for pollinator attraction. However. the short floral longevity and the production of mostly one inflorescence per plant make it s pollination potentially dependent on strong flowering synchrony and on ex ternal factors not controlled by the plant (the pollination context). The f lowering period in both sites lasted >3 mo. Day-to-day variation in simulta neous antheses was high. and 11-50% of antheses occur-red on days during wh ich no pollen donor was present. Inflorescence traits, flowering synchrony, and between-plant distance all influenced infructescence and fruit initiat ion. but their relative importance differed between sites. In one large pop ulation, infructescence initiation was positively related to inflorescence traits: in a smaller population infructescence initiation increased with th e number of donor inflorescences. In both sites. percentage of fruits initi ated per infructescence was dependent on a combination of inflorescence tra its, flowering synchrony, and between-plant distance. Plants producing 2-4 inflorescences had higher probability of infructescence initiation and over lapped their antheses with more plants than single-inflorescence ones.