Complex sentence: Cucurbitacin is a plant steroid poisonous to mammals found in wild "Cucurbita" in quantities sufficient to discourage herbivores, and in each member of the "Cucurbitaceae" family.
Split into simpler sentences: Cucurbitacin is a plant steroid poisonous to mammals found in wild "Cucurbita" in quantities sufficient to discourage herbivores. It is found each member of the "Cucurbitaceae" family.