If one plant is named salvia greggii and another is named salvia vanhouttei, what does this tell you about these plants?

It tells us that they are the same species accept they have small differences that they have to adapt to their environment. 

Good Luck! :) 

So the order of classification is DKPCOFGS;
Domain, Kingdom, Phylum, Class, Order, Family, Genus, and Species.

The answer to this question is that they are part of the same Genus which inlcudes Domain, Kingdom, Phylum, Class, Order, and Family, but are a different species under the genus.