I would like to bring an example of a button-flowered type to your attention. In 2006, I planted two species of this type in a parking lot garden, the rare New England Blazing Star (L. scariosa Var. novae-angliae), the only Liatris native to all of New England, and Appalachian Blazing Star (L. squarrulosa Var. earlei). After 4 years, the New England Blazing Star has petered out, but the Appalachian Blazing Star is getting stronger. (Soil conditions on this site may be more attuned to the Appalachian species, whereas the New England species prefers sandy soils.) Besides being really drought resistant, this season it survived over 6 weeks of mid-summer temperatures on less than 2 inches of rain, it blooms several weeks later later than the spike-flowered forms.
This first photo shows it near the end of July, just beginning to open. The L. spicata had finished blooming a couple of weeks earlier. The second photo shows it still going strong at the end of August.