Shy wallflower

Where does that phrase come from about shy, retiring wallflowers? I have been growing wallflowers in my garden for a couple of years now and they are anything but shy and retiring. They seem to be quite resilient and some of the earliest signs of spring returning. Like little gems sprinkling golden yellow and orange across the garden. Below is a photo that I took of such a sparkling gem. Dazzling amongst the bare stems and tree trunks, with a crown of buds above.

And it inspired a haiku:

yellow dots

wallflower

pointillist painting