From a taxonomic standpoint, I am unsure of their relationship, though they do look alot alike and sometimes are sold (incorrectly) as Ageratums.
Found this little bit about them...
"This strikingly beautiful shrub comes from the cloud forests of Mexico. The large velvety heart-shaped leaves are purplish green with purple veining, dark purple beneath. Young growth and stems are deep maroon-purple with large bluish violet ageratum-like flower clusters in spring. Fast growing to 4 feet high. Needs bright shade and ample water. Can be grown in a cool greenhouse in large pots in the winter (minimum temperature 35F) and then brought outdoors in spring and summer. Give frost protection. USDA zones 9 - 11.
With hundreds of Ageratum, Bartlettina, and Eupatorium species, the proper identification of this plant is uncertain. It is sometimes offered elsewhere as Ageratum corymbosum, but it does not fit the botanical description for A. corymbosum (flat-top whiteweed, desert ageratum). Also, listed by another grower as Ageratum 'Azure Skies'. The typical Bartlettina sordida has greener leaves and is larger growing. Our guess is that this is probably a variety or subspecies of Bartlettina sordida or a closely related species."
http://www.kartuz.com/pc/80126...
