Interestingly, Opuntia helleri relies on birds to aid pollination, as the northern islands occupied by this cactus are not inhabited by any suitable insect pollinators (7). A number of bird species visit Opuntia helleri, including doves, cactus finches and mockingbirds. The soft-spines allow easy access to this species’ flowers, and while feeding on the pollen, nectar and even petals, the birds receive a dusting of pollen which is transferred to, and fertilises, the other flowers visited (4) (7). This adaptation to bird pollination is only possible because the absence of large, herbivorous reptiles, such as giant tortoises, from the northern Galapagos Islands, allows Opuntia helleri to survive without the protection of hard, sharp spines (8) (9).
Despite producing flowers all year round, Opuntia helleri’s main flowering season occurs between November and February (9). Interestingly, even if the flowers are not pollinated, fruits and seeds may still develop. This is due to a remarkable process called apomixis, in which the female, unfertilised gametes develop into an embryo without needing to fuse with male gametes (10). Whether pollination occurs or not, fruits take several months to mature. Eventually dropping off the pads, many of the fruits are consumed by mockingbirds and cactus finches, which later pass the seeds in their faeces, thereby helping Opuntia helleri to disperse its offspring (7).
Flowering only occurs in larger specimens of Opuntia helleri (8), but individuals of any size can reproduce simply by dropping their pads. In a process called vegetative reproduction, an entirely new plant may grow from the detached portion, giving rise to large thickets of cacti, all of which are genetically identical (7).