The triterpene saponin suspected of causing toxicity in cyclamen roots and bulbs is cyclamin.
Cyclamin is a triterpenoid pentasaccharide saponin found in several Cyclamen species, including Cyclamen persicum, the familiar florist’s cyclamen. Its molecule combines a sterol-like triterpenoid backbone with five linked sugar groups, giving it amphipathic, surface-active properties typical of saponins.
Cyclamen toxicity is concentrated especially in the underground parts: the plant’s corms, often loosely called bulbs, and roots. Eating them can cause gastrointestinal illness, including nausea, vomiting and severe diarrhea. Cyclamin has also been investigated for cytotoxic effects and has appeared as an ingredient in some nasal preparations, but its toxicology and precise mechanism are not fully understood.
A common mix-up is confusing cyclamin with escin, another plant saponin associated with horse chestnut. The answer is not a general class such as “saponin”; cyclamin is the named compound specifically suspected in cyclamen’s underground-part toxicity.