Article: A new multiple-floated Azolla from the Eocene of Britain with a brief review of the genus

Megaspores and microspore massulae of Azolla colwellensis sp. nov. are described from the Upper Eocene, Upper Headon Beds of Colwell Bay, Isle of Wight. The megaspores possess a multifloated 'swim apparatus' with three tiers of floats. The floats are arranged in three groups of six. There is a distinct collar at the junction with the megaspore zone and hairs arising from this collar enmesh the floats. The microspore massulae possess occasionally septate, grapnel-tipped glochidia. This species is the youngest multifloated Azolla yet recorded and is the only multifloated species which possesses a collar. It further supports recent hypotheses that a number of lines of evolution have been involved in the development of extant Azolla species. A review of the sixty species recorded in the genus Azolla is presented in the form of a table showing stratigraphic ranges and features of the megaspores and massulae. Certain species are discussed in detail with relation to the morphology of A. colwellensis.