H. helianthoides appears to be self-incompatible. Here's the data I collected:
I've also started my data analysis in R. It's not done yet, but here's what I have so far:
Basically, styles persist significantly longer when self-pollinated or not pollinated than when cross-pollinated. However, in the top rows of florets on each flower head, style persistence does not differ as much between the treatments (because all the styles in these rows shrivel rather quickly). Therefore, when using style persistence to study other aspects of this species' breeding system (ex. pollinator efficiency, compatibility of specific individuals), one should use the bottom several rows of florets. In these rows, cross-pollinated styles always shrivel within three days of pollen application, whereas styles that do not receive compatible pollen never shrivel so quickly.
As I mentioned before, I was unable to collect much quantitative data about C. palmata style persistence. But I did notice some things that might be helpful to anyone interested in studying this species further. The following document gives a brief summary:
C. palmata Summary.doc