This, my friends, is a Buffalo Gourd plant. It's also called a Stink Gourd. I've seen these things growing all over the Park. They sprawl on the ground and sport large yellow flowers that turn into round, green fruit. I had always assumed that the plants were zucchini or other squash plants that had been transplanted by birds and cross-pollenated with something weird. But no, they are their own entity. Again, this one grows off the trail in a spot that is rarely mowed. The blooms had just shriveled, as you can see.
I was surprised to discover that the plants are called Stink Gourds. I have never noticed any smell. Nor did the authors of my wildflower handbook, Campbell and Lynn Loughmiller. Here's what they say, "The plant supposedly gets the name 'stink gourd' from its foul odor, but we handled the fruit and dissected the blossoms without noticing any unpleasant odor." Probably some mean elementary-school kid gave the gourd a sucky name that stuck.
Where I grew up in New Jersey, we had a weed called Skunk Cabbage, and it really did smell like its namesake. It grew prolifically. What you did was pull it out of the ground and then break its stem, releasing the skunky juices. Then you chased around the kid who was beneath you in the social pecking order. Heh. Also, we had a plant called a Mayapple. It was only about 6 inches tall, but it produced many small, hard, green, apple-shaped fruits that were excellent bruise-making projectiles. I lacked decent eye-hand coordination, so I got pelted pretty regularly, unable to fight back. Snowball fights were a similar situation. So if I see anyone coming after me with a stink gourd, I am so out of here.
Quotation from Texas Wildflowers: A Field Guide (1994, UT Press), p. 90.