The gargantuan bud of a pelican flower (Aristolochia grandiflora) droops down near the forest floor, somewhat resembling a reddish nautilus suspended in the air. Brushing up against it, the hollow ballooning structure had a faint mellow resonance and the venation felt tough despite its weightless. Aristolochia flowers are some of the largest in the world, making them difficult to remain undetected for any wandering naturalist or herbivorous animal that would make quick work of the fleshy meal. In fact, tens of meters higher above this flower bud, several flowering Aristolochia disappeared one after the other over the course of a few days. The following day after I took this picture, this one had been consumed as well— unable to fulfill its reproductive life stage. For all of these flower casualties, I strongly suspect a family of spider monkeys was responsible.
Aristolochia has a rich diversity in the mechanisms of pollination. Most emit a foul carrion-like scent (like the famous Rafflesia), enticing flies by mimicking the smell of decaying organic matter, fungi, or dung as a brooding site. Others share similar semiochemicals with mirid bugs as a food source (kleptomyiophily) or pheromones as a mating cue. In some cases, the flower and its fly pollinators are mutualistic to a degree, in which Aristolochia achieves pollination and the flies benefit from either a substrate for larval development, a food source (e.g., secretions from nectarioles), or a high rate of encounters with potential mates. At the other extreme, floral deception in certain Aristolochia species is solely beneficial to the plant and their pollinators reap no rewards.
Like many others in the genus, the flower of Aristolochia grandiflora is hermaphroditic and short-lived, blooming for only two days. Carrion-like odors and deep red-purple colors initially attract flies to the flower, and they are guided within the large complex flower structure via light gradients that take advantage of the flies’ attraction to light, and the interaction between the flower’s translucent surface and the ambient light environment. Eventually, they arrive at the inner column (gymnostemium) where pollen carried by the flies is deposited on the stigma. This triggers a structural change in the flower that entraps the flies, rendering them unable to escape from the narrowing trichome-lined cavity. Pollen is then released onto the flower’s temporary prisoners, and the flower eventually relaxes and releases its pollinators prior to withering away. In the evolutionary history of Aristolochia, it is hypothesized that as pollinators were harbored for longer periods of time, nectar provisioning arose secondarily to alleviate fly mortality and prolong survival. Due to the vast number of associations these giant flowers have with tons of insect species, the ephemeral microenvironments of blooming Aristolochia are surely conducive to the evolution of a plethora of symbiotic relationships.
Interestingly, Aristolochia grandiflora has long been used for its medicinal properties by indigenous communities, particularly to reduce hemorrhaging after snakebite (commonly from terciopelos). The species has a moderate neutralizing ability of proteolytic effects among over 70 plant extracts examined, so I’ll have to keep that in mind if I’m ever so unfortunate.