Psilotum nudum, known as the whisk fern, is a fernlike plant. Like the other species in the order Psilotales, it lacks roots. It is found in tropical Africa, Central America, tropical and subtropical North America, South America, tropical Asia, Australia, Hawaii, southern Japan, Lord Howe Island, New Zealand, with a few isolated populations in SW Europe ("Los Alcornocales", Spain, Cádiz province).

Its name, Psilotum nudum, means "bare naked" in Latin, because it lacks most of the organs of typical vascular plants, as a result of evolutionary reduction.

In tropical areas, this plant is often epiphytic, whilst in more temperate areas, such as south-eastern Australia, it is usually found growing in rock crevices. Thousands of people per day walk by these plants at the Sydney Opera House forecourt.