thwarts is a form of:

Lungwort



ENGLISH MEANING
noun
1.
An herb of the genus Pulmonaria (P. officinalis), of Europe; -- so called because the spotted appearance of the leaves resembles that of a diseased lung.
2.
Any plant of the genus Mertensia (esp. M. Virginica and M. Sibirica) plants nearly related to Pulmonaria. The American lungwort is Mertensia Virginica, Virginia cowslip.