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
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Warfarin is found in sweet clovers. Its story is really fascinating; I recommend having a look at this video on the topic [1]. For hardcore people who're into pharm, the story is also reported on Goodman & Gilman. [1]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).
Codeine is the prodrug of morphine, which in turn is a opiate. I bet you know where it comes from.