I usually don't paint flowers. I struggle with some of the color with my three color palette and the drawing and rendering can be a little complicated and delicate. When done right though they are of course gorgeous. I submit Richard Schmid and Dan Gerhartz right off the top of my head.
But I do have a couple I like to paint. And they are both weeds. Mention them here in Middle Tennessee and the farmers cringe. One is the Creeping Buttercup and the other is the Thistle. The thistle has about as much character to me as anything. They have a long Celtic history and are the national flower of Scotland and are prickly and tough and will grow anywhere with a little sun. And when they bloom they're beautiful . Beautiful, tenacious, delicate and full of character. Yikes, I just described my two daughters to a tee.