First insights on the reproductive biology of Anarthrophyllum strigulipetalum (Fabaceae), a rare bird-pollinated species from semi-arid Patagonia

We present the first empirical information on floral traits, floral visitors, and breeding system of Anarthrophyllum strigulipetalum, a rare and charismatic plant species that inhabits rocky terrains in the harsh semi-arid landscapes of northwestern Patagonia. Despite being large plants (∼1.7 m² surface area), with a showy floral display (>100,000 flowers/plant), protracted flowering period (∼1 month), high nectar production (16.7 μl per flower), high pollen viability (96%) and pollen receipt (∼200 grains/stigma), species reproductive success was very low, with less than 1% of the flowers developing into fruit. Only birds triggered the flower-opening mechanism and carried pollen, whereas insects behaved as nectar thieves. The addition of nectar seemed to increase fruit formation compared to control flowers, whereas nectar removal tended to decrease fruit set. The natural low fruiting levels could be the result of a combination of factors such as low legitimate pollinator visitation rate, low-diverse and poor-quality pollen receipt due to geitonogamy promoted by the great floral display and the abundant floral reward, intense levels of nectar theft by native insects, and even climatic stress. The reduced size of populations and low fitness settles the grounds for potentially low genetic diversity, inbreeding depression and, ultimately, demographic declines.