Which plant species is noted for being toxic?

Senecio longilobus is recognized for its toxicity, particularly because it contains pyrrolizidine alkaloids, which can cause serious health issues if ingested. These compounds are known to be hepatotoxic, meaning they can damage the liver and lead to severe illness or even death in animals and humans. The presence of these toxic alkaloids is a significant factor in the plant's dangerous reputation.

In contrast, the other plant species listed are generally not regarded as being notably toxic. For instance, Gnaphalium sp. (commonly known as cottonweed) may have some medicinal properties, and while there can be concerns about certain species, they are not primarily labeled as toxic. Harpagophytum procumbens, also known as devil's claw, is primarily recognized for its anti-inflammatory properties and is often used in herbal medicine with a low toxicity profile. Folium as a term is quite broad and does not specifically refer to a single toxic plant, so it lacks the context needed to be categorized as such.

Therefore, the identification of Senecio longilobus as a toxic species is well-supported by its chemical composition and the associated health risks.