Back in the dry season they were just brown, dead- looking vines entangled in the chain-link fence along the road to the reservoir, but even then I could see that the vine was something different from normal morning-glories. For, the fruit-capsules were big yet produced only four or fewer seeds per capsule. Also, the split-open fruits looked like silver-dollar-size, woody stars, something I'd not seen.
When the flowers came with the rainy season they looked like morning-glory flowers, except that their pollen-producing anthers were strongly twisted. Moreover, the vine produced Virginia-creeper-like leaves instead of the usual heartshaped morning-glory leaves. You can see a flower, leaf and unopened flower-bud below:
The vine is MERREMIA DISSECTA, sometimes in English called Alamo Vine, and sometimes, because of those star-shaped, woody, split-capsule remains, Woodrose. It's a genuine member of the Morning Glory Family but in a genus we don't hear much of. Many Merremias produce yellow flowers, despite our Alamo Vine's white ones.
The vine is distributed from the southern US through Mexico to northern South America, and the Caribbean.