What Do Hollyhocks Look Like When They Start To Grow - Garden Work

Hollyhocks will cross pollinate and if you have several kinds you can't say with a certainty what color your new seedling will be. Mallows like zebrina mallow is different than hollyhocks, Anastastia. You know what M.D.

means, but what does D.O. mean? What's different and what's alike between these two kinds of health care providers?