A “monstrous” fern frond. One of the fronds of the fern Phlebodium areolatum collected by Darwin on Charles Island (Floreana) in October 1835 was a “monstrous” form. It is labelled “Pleopeltis aurea var.” on the herbarium sheet. This frond has four equal-sized and very large “pinnae” all originating from a common point rather than displaying the usual pinnate leaf form typical of this species.
Henslow and Darwin were both intrigued by this form of variation and puzzled over its significance in plant development. Henslow collected examples of “monstrosity” in many species of ferns and flowering plants, and wrote several papers about this phenomenon.