Excerpts from Jim Conrad's
Naturalist Newsletter

Pentalinon luteum vine overgrowing fence

from the September 11, 2011 Newsletter issued from Mayan Beach Garden Inn 20 kms north of Mahahual, Quintana Roo, México
YELLOW-FLOWERED VINE WITHOUT A GOOD NAME

Several times daily I duck below a luxurious mass of densely tangling vine overgrowing the beam above the gate leading to the kitchen. The vine bears large, yellow, trumpet-shaped flowers. That's it above. A close-up of the 2.5-inch long (6cm) flowers is shown below below:

Pentalinon luteum flowers

There's a commonly planted, similarly robust vine with similarly trumpet-shaped, yellow flowers planted throughout the world's tropics (next section), often called the Golden Trumpet Vine. The kitchen gate vine is something else. The evidence for that is shown below:

Pentalinon luteum flower throat showing anther appendages

That's a view down the throat of one of this vine's flowers. The corolla tube is yellow with narrow, red lines radiating from the center, exactly as with the Golden Trumpet Vine, but what are those yellow, curly things lying on the throat's floor? In the next section we'll see that they're completely missing in Golden Trumpet Vine flowers.

Each of those five curly things arises atop one of five anthers. They are "anther appendages" and I'm guessing that they provide footholds for visiting pollinators. Like the red lines, the appendages also serve as nectar guides pointing toward access to nectar at the flower's base. In a blossom's longitudinal section you can see how the anthers join like a tepee over the blunt stigma head, with the curly appendages arising from their tips, below:

Pentalinon luteum flower throat showing anther appendages, longitudinal section

The vine is PENTALINON LUTEUM, and if you need a commonly accepted English name you're out of luck. Lots of names can be found for it but none seems more used than any other. There's Yellow Mandevilla (though it's not a Mandevilla), Yellow Dipladenia (not a Diplandenia), Wild Allamanda (not an Allamanda), Lice Bush, Wild Wist, and then there's the USDA's inlikely Hammock Viper's-tail.

The species is mostly Caribbean in distribution. I see it growing wild at the edges of mangroves here but can't decide whether the plants are natural, or have been swept there from gringo beach properties rearranged by hurricane storm surges. {Note: Later I decide that what I'm seeing growing wild is the closely related Pentalinon andrieuxii}

As is often the case with members of the Dogbane Family, all parts of Pentalinon luteum are poisonous if ingested, and even handling can cause skin irritation.