@cwarneke @castillejajosie
I selected these observations when looking through most of the observations of yellow starthistle in California.

In my favorites there are some observations of interesting yellow starthistle.

Short and long spines can be present on the same flower head or plant. Intermediates have less long and thick spines. It looks like mature and brown seed heads have longer spines than green heads. Mowing does not appear to have great effect on the appendage length.

Mei Sun, D. M. Maddox, Mayfield, and DiTomaso have researched yellow starthistle. Sun concluded that populations were variable genetically. less ↑