## Core Concept
The question refers to a plant source that produces a penicillin-like or antibiotic substance, which can be used as an alternative or supplement to traditional penicillin. This concept falls under the realm of **botany** and **pharmacognosy**, specifically focusing on plants with medicinal properties.

## Why the Correct Answer is Right
The correct answer, **C. Calotropis**, is right because *Calotropis* species, commonly known as milkweed, produce compounds with antimicrobial properties. One of the notable compounds from *Calotropis gigantea* and *Calotropis procera* is penicillin-like substance, although not exactly penicillin, which is produced by fungi.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it does not specify a known plant source of penicillin or antibiotic substances.
- **Option B:** This option is incorrect as it does not correspond with a recognized plant source of antimicrobial compounds similar to penicillin.
- **Option D:** This option is incorrect because it does not accurately represent a plant known for producing penicillin-like substances.

## Clinical Pearl / High-Yield Fact
A memorable point for students is that while *Calotropis* species have been studied for their medicinal properties, including antimicrobial activity, traditional penicillin is derived from fungi, specifically *Penicillium* species. This highlights the diversity of sources for antimicrobial compounds.

## Correct Answer: C. Calotropis.