If you compare Argentina Skies with Black and Blue versus other guaranitica forms like Van Remsen, Blue Ensign, and the old ambigens, you can see the resemblance between the first two and the difference with the second group of three. AS was selected from a population of variously colored forms in the wild and is, along with B&B, a form of guaranitica that was once identified as S. melanocalyx, then combined, along with ambigens, into guaranitica.