I've been growing increasingly interested in geraniums and stumbled upon these great resources describing some of the different series of zonal and ivy geraniums which might be helpful.

BullsEye, Elite, Maverick, Multibloom, Orbit, Orbit Synchro, Pinto, Pinto Premium, Ringo 2000, Tornado: http://farmer.hu/PDFkatalogusok/Goldsmith2012.pdf

Rocky Mountain, Classic, Amaricana, Calliope & Caliente, Exotic, Fidelity, Tango, Contessa, Freestyle, Temprano, Cascade, Blizzard: http://www.syngentaflowers.com/country/us/en/Vegetative/Documents/Catalog/Geranium%20Brochure.pdf

F1 Quantum, Summertime, F1 Moulin Rouge, F2 Cabaret, F2 Dancer, F2 Inspire, F1 Divas, F1 Horizon: http://floranova.com/products/geranium

This makes sense to me now, I was wondering why some of the geraniums I was purchasing have such different growth habits!