Petaloid staminodes enhance pollinator attraction and seed set in an arid-adapted plant

Staminodes (sterile stamens) are widely interpreted as enhancing pollination through pollinator attraction and efficiency, yet their contribution to seed production remains uncertain in species with petaloid staminodes, short anthesis, and arid habitats where opportunities for pollinator attraction may be restricted. We tested how petaloid staminodes influence pollinator behaviour and seed set in Mentzelia integra (Loasaceae), an arid-adapted species with short-lived, evening-blooming flowers, using paired-choice field experiments near St. George, UT, USA. We compared paired intact and staminode-removed flowers for visitation rate, first landing, visit duration, flower constancy, and seed set. Flowers with intact staminodes received more bee visits and first landings, whereas visit duration did not differ between treatments in Perdita, the only taxon analysed for this metric, suggesting a primary role in attraction rather than handling efficiency. Previous flower type influenced subsequent landing choice in Megachile and Perdita, but not in Anthophora. Only Perdita showed a reciprocal transition pattern consistent with flower constancy, with subsequent landings tending to remain within the same treatment. Flowers with intact staminodes had higher seed set than flowers without staminodes. Overall, petaloid staminodes in M. integra enhance seed set through attraction-mediated pathways, highlighting the evolutionary co-option of sterile staminal structures as floral display traits.