Comparative morphology and anatomy of fruits and seeds of the endemic Caribbean genus Elekmania (Senecioneae, Asteraceae)

Fruit and seed anatomical characters are valuable sources of evidence in systematic studies of Asteraceae, yet remain largely unexplored in many genera of Senecioneae (Asteroideae), including Elekmania, an endemic Caribbean genus with nine species segregated from Senecio s.l. We investigated the morphology and anatomy of the pericarp and seeds across all nine Elekmania species. Morphological and anatomical analyses were performed using light and scanning electron microscopy. Cypselae were generally tubular to turbinate and exhibited interspecific variation in indumentum and carpopodium differentiation. The pericarp was consistently organized into an uniseriate exocarp, a parenchymatous mesocarp with fibrous bands restricted to the rib regions, and a crushed endocarp. In most species (Elekmania barahonensis, Elekmania domingensis, Elekmania fuertesii, Elekmania kuekenthalii, Elekmania marciana, Elekmania picardae, and Elekmania samanensis), secretory ducts surrounded by fibres occurred on the outer side of the vascular bundles, contrasting with patterns reported for other Senecioneae and with comparable secretory spaces described in Anthemideae. The pappus was uniseriate and non-vascularized, and the carpopodium exhibited an exocarp composed of cells with characteristics similar to gelatinous fibres. The seed coat lacked a mechanical layer, bore prismatic crystals in the mesotesta, and exhibited a consistent raphal vasculature pattern. Secretory ducts were also present in the cotyledons of all species examined. Our results indicate that fruit and seed anatomy provide a complementary, character-rich dataset for species delimitation in Elekmania and reveal patterns relevant to exploring generic limits and structural evolution within Caribbean Senecioneae lineages, where morphological convergence has long challenged delimitation.