Architectural traits underlie growth form diversity and polycarpic versus monocarpic life histories in Cerberiopsis (Apocynaceae)

Plant architecture strongly influences plant growth habits, as it determines the arrangement, function and fate of meristems. How architecture could be involved in the monocarpic life history, i.e. dying after flowering, remains poorly investigated. Monocarpy is evident in some species since they are annual or because their single stem flowers apically. However, monocarpy in long-lived branched trees is rare and remains poorly understood. We aim to highlight the architectural features involved in the monocarpic strategy of Cerberiopsis candelabra, a rainforest tree endemic to New Caledonia. We conducted a comparative analysis of the genus, which comprises three species with different growth habits. Twenty plants of each species were studied at different ontogenic stages. We compared their developmental sequence and analysed their processes of growth, branching, flowering and reiteration. We identified a combination of traits that distinguish the species, and we found a syndrome of two architectural features that support the monocarpic strategy in C. candelabra: the synchronous flowering of all terminal meristems and the absence of delayed branching. Flowering in C. candelabra preferentially occurs when the complete architectural sequence is developed, but the plant never shows signs of senescence, suggesting that environmental stresses, such as wind disturbance, could be the main trigger for flowering. The architecture of C. candelabra is suggested to be the most derived in the genus.