Sentence:  If thou return not, Gammer o'er her pail / evermore the petlings, with sad brow, / Will look for thee upon the holly bough, / Where thou didst chirp thy signal note, ere on / The lowly <WSD>grunsel</WSD> thou didst light ... 
Meaning of the word marked with <WSD> tags:  Variant of groundsel, any of several species of "Senecio", a genus of the daisy family.