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People can be infected by bacteria, viruses, fungi and animal parasites, but are any human or animal diseases caused by plants? Is it possible to suffer a moss infection, come down with a bad case of the ferns, or contract wisteria? If not, why have no plants taken advantage of us in this way?
• Plants do cause disease. Think of allergies to plants such as poison ivy or products such as peanuts. Ailanthus (also known as the tree of heaven) bears flowers whose smell has been associated with headaches and nausea.
But these are not infectious diseases. Plants do not become pathogens inside us as they need light for photosynthesis, which they can't get inside our bodies.
Eric Kvaalen, La Courneuve, France
• I know of no vascular plants that are truly infectious in animals, though some do infect ...