Alsomitra macrocarpa seed (syn. Zanonia macrocarpa)
Kebun Raya, Bogor, Indonesia.
A bit of flowery prose from a published essay that I wrote in 2001 on wind-dispersed seeds & fruits:
"Every now and then, field botanists are treated to transcendental moments when the light is golden, the air is fresh, interesting plants are at hand, and the hardships of field work just melt away. During those times, scientific insights arrive with astonishing clarity and grace. One such moment for me came on a sunny afternoon in the Kebun Raya Botanic Garden, in Bogor, Indonesia, some years ago. On that memorable day, I was transfixed as I watched dozens of winged seeds of Alsomitra macrocarpa (Cucurbitaceae, the squash family) glide to the ground in broad, lazy spirals. The seeds spilled out from a fruit hanging on the liana climbing on one of the enormous old trees in the garden. All the principles of aerodynamics as they relate to seed dispersal were manifest in that one lovely moment.
"The gliding seeds of Alsomitra exhibit two kinds of motion: The forward gliding motion, which takes the seed on a helical, downward path, and phugoid oscillations, in which the gliding seed gains lift, stalls, drops briefly until it accelerates enough to generate lift, starting the process over again. Phugoid oscillations are well known to aviation engineers and model airplane fliers, because they can destabilize mechanized flight, but in the seeds of Alsomitra, phugoid oscillations add a graceful rhythm to the descent, and more importantly, slow the descent of the seeds giving them more time aloft. Time aloft is the sine qua non of successful dispersal by wind."