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.
In the background is another native, Stiff Goldenrod, Solidago rigida (which has recently been changed to Oligoneuron rigidum). This is one of the earlier blooming of the goldenrods.**
This last photo is of the New England Blazing Star taken last year at the Wild Flower Meadow at Mount Auburn Cemetery. The conditions on this site are less severe than those experienced in the parking lot garden. One difference between these two species is that the flower heads are relatively broader than on the Appalachian blazing Star. While the Cup-flowered Liatris are not what many people expect to see when they are asking for some Liatris for their garden, they are a way of extending the season for another 4-6 weeks, and the pollinators don't mind one bit. Unfortunately, these plants are not broadly avalable at regular nurseries, I got mine from the New England Wildflower Society, an excellent source for native plants in the Boston area.
**Just a note about goldenrods. As I explained to a friend who asked about these plants today, Goldenrod pollen is not the cause autumn hayfeaver, its pollen grains are too heavy and sticky to float through the air. The main culprit for causing hayfever at this time of year is ragweed.