Hawkweed n. : A plant of the genus Hieracium; -- so called from the ancient belief that birds of prey used its juice to strengthen their vision.

Hawkweed n. : A plant of the genus Senecio (S. hieracifolius).

Example:
other than Pisum sativum , which plants did Mendel work on?

Taxonomy
Hawkweed, Hieracium, Orange Hawkweed, species, Yellow Hawkweed, unranked, genus Hieracium, Snowdonia hawkweed, Mouse-ear Hawkweed, free encyclopedia, Pilosella, White-flowered Hawkweed, Alpine Hawkweed, Roughstem Hawkweed, Hieracium aurantiacum, genus, Asteraceae, King Devil.

Defination from the web:
Hawkweed refers to any species in the very large genus Hieracium and its segregate genus Pilosella, in the sunflower family (Asteraceae) ... Hawkweed is a slang name taken from folklore which says that hawks would chew on the plant to improve their eyesight. ...