SoulGrower, yeah, until this discussion I was under the impression Alba and Carthagenesis were different names for the same plant.
The two leaves packed in with the nexus plantlet are definitely Nexus. They were from a young plant so I wouldn't count on them having all the characteristics of a mature Nexus yet. I'll check my larger Nexus plants to see what characteristics they have (though all of my nexus plants are < 8mo old).
Of the four leaves in the bag labeled "Alba", two were slightly larger and wider. They are Alba. Originally gotten as leaf cuttings from WSS 2 years ago. I trust their ID. The other 2 that are slightly smaller & narrower are from a seller named Visionary Botanicals on ecrater.com. They were sold as viridis, but when I noticed the wavy leaves, and how they don't go all the way to the stem, and white flowers, I figured it was just another Alba... but now I'm second guessing that. So if you can figure out which of the four leaves those were, probably best to label them as "Mystery Psychotria" for now:-p