Penicillin is indeed the only in the group not to be plant-based. It comes from a mould (fungus) with antibacterial propertis, as observed by Fleming in the distant 1928. https://en.m.wikipedia.org/wiki/Penicillium
Warfarin is found in sweet clovers. Its story is really fascinating; I recommend having a look at this video on the topic . For hardcore people who're into pharm, the story is also reported on Goodman & Gilman. https://tube.cadence.moe/watch?v=OnzF0oJkYe0
Vincristine (a chemotherapic), like other alkaloids with antiblastic/cytostatic properties, is derived from 'vinca rosacea', commonly referred to as 'bright eye' (pic below).
"I appreciate SDF but it's a general-purpose server and the name doesn't make it obvious that it's about art." - Eugen Rochko