дернинки

I was reading the article http://www.botanichka.ru/blog/2015/1...teniya-v-sadu/ and encountered the following sentence:

Это лекарственное, но оттого не менее красивое растение с резной зеленью образует плотные дернинки, на которых словно пуговки светятся мелкие желтые цветки в верхушечных соцветиях.

The sentence makes good sense except the word дернинки is unfamiliar. The closest I could get to a definition for the word is sod, however that doesn't work in this context. By extension it would make sense that an alternative translation would be groundcover. The use of зеленью a couple words before it also supports this interpretation.

Does anyone have a solid definition for дернинки?

It's a mangled dimunitive of дёрн "greensward"