Just noticed that my Argentina Sky salvia started blooming. Senior moment, can't remember the correct word for the stems but thought they were neat to photograph.
Argentina Sky blooms
They are quadrangular, with the four vascular bundles at the corners of a square, protruding to form ridges. Salvia madrensis does this to an almost ridiculous degree, and maintains the ridges as it gets bigger. Guaraniticas seem to evolve into more of a round shape as the stem grows.
Or perhaps are you referring to the pigmentation in between the corners?
Thanks Rich for the info. I also like the way the flower spikes were developing.