Excerpts from Jim Conrad's
Naturalist Newsletter

from the August 20, 2018 Newsletter issued from Rancho Regenesis in the woods ±4kms west of Ek Balam Ruins; elevation ~40m (~130 ft), N20.876°, W88.170°; north-central Yucatán, MÉXICO
HEAVY CROP OF AMPELOCISSUS
This week I found a vine loaded with fully formed, healthy-looking grapes or grape-like fruits, shown below:

AMPELOCISSUS ERDVENDBERGIANA, clusters of immature grapes

Those are immature. A bunch of ripe one is shown below:

AMPELOCISSUS ERDVENDBERGIANA, cluster of mature red grapes

In that cluster, the bright red grapes are still too hard and bitter to taste good. The darker, purple or "grape-colored" ones are as sweet and tasty as you'd want, though compared to store-bought grapes their seeds were fairly large in relation to their flesh, as you can see below:

AMPELOCISSUS ERDVENDBERGIANA, seeds inside open grape

Leaves are shown below:

Ampelocissus, leaves

The leaves' undersides are soft-hairy and silvery, as shown close-up below:

AMPELOCISSUS ERDVENDBERGIANA, hair and glands on leaf undersurface

NOTE: At first I identified this as the Caribbean Grape, Vitis tiliifolia, because on the Internet other pictures like ours were identified as that. However, Jean-Benoit Peltier in Montpellier, France wrote saying that it looked like an Ampelocissus, with which I agreed. Jean-Benoit directed Julio Lombardi in São Palo, Brazil, an expert in tropical American grapevine species, to this page, who identified it as an Ampelocissus, perhaps A. erdvendbergiana, which has been documented for the Yucatan. Says Dr. Lombardi: "On internet, it is very confused."
Along the leaf's midrib crossing the image's center you can barely see among the taller pale hairs very short, honey-colored stalked glands.

This species is fairly common in the forest surrounding the rancho, but normally it doesn't grow in dense shade and doesn't produce much.