I'm with Schledog.It's a tradescantia. They are super easy to propagate and I see them for sale pretty often in garden centers so I didn't know they were hard to find for some. I don't recommend it for a viv if you want it to look good because it gets leggy and it's pretty weedy but its a great plant for breeder and grow in tanks.
It's definitely a tradescantia, often called the Wandering Jew. I have a few varieties in my garden, and they will do well in tanks. They are so common that, ethical issues aside, there's no reason to attempt collection from the wild. They're gorgeous plants.
El yunque! Oh, man, I wish we could trade places. That's one of the most beautiful locations in the world! I've hiked the aquaduct trail there, and it's just amazing. I hope you'll post lots of photos.