Heather Angel / Frog (Rana temporaria) spawn amongst invasive Fairy fern (Azolla filiculoides) from garden pond. Photographed in aquarium, controlled conditions. Surrey, England, UK. March.

Heather Angel / Fairy fern (Azolla filiculoides) and Water forget me not (Myosotis scorpioides) in frozen garden pond. Surrey, England, UK. January.

MYN / Dirk Funhoff / Floating watermoss (Salvinia natans), Lindenberg, Pfalz, Germany. October. Meetyourneighbours.net project

MYN / Dirk Funhoff / Floating watermoss (Salvinia natans), Lindenberg, Pfalz, Germany. October. Meetyourneighbours.net project

Chris Mattison / Fairy moss (Azolla filiculoides) a floating fern.

Jack Dykinga / Canyon pool with Water Shamrocks (Marsilea mucronata) floating. Coronado National Forest, Peck Canyon, Atascosa Mountains, Arizona, November.

Adrian Davies / American Water Fern (Azolla filliculoides) invasive species, growing in pond in Surrey, England.

Adrian Davies / American Water Fern (Azolla filliculoides) invasive species, growing in pond in Surrey, England

Bruce Thomson / Eastern dwarf tree frog (Litoria fallax) resting on Red water fern (Azolla sp.) in shallow pond at night, Border Ranges, Queensland, Australia.

Jack Dykinga / Cypress dome swamp with water surface covered with Water-spangles (Salvinia minima) and Duckweed (Lemna), Big Cypress Seminole Indian Reservation, Florida, USA.

Doug Gimesy / Aerial view of a section of Middle Reedy Lake with floating mats of Water fern (Azolla sp.) Tangled lignum (Duma florulenta) Reeds (Typha sp.) and Water primrose (Ludwigia peploides) Kerang, Victoria,...

Doug Gimesy / Aerial view of a section of Middle Reedy Lake with floating mats of Water fern (Azolla sp.) Tangled lignum (Duma florulenta) Reeds (Typha sp.) and Water primrose (Ludwigia peploides) Kerang, Victoria,...

Doug Gimesy / Aerial view of volunteers from Native Fish Australia) and Austral Research and Consulting checking bait traps by canoe for endangered Southern purple spotted gudgeon (Mogurnda adspersa). Part of capti...

Doug Gimesy / Aerial view of a section of Middle Reedy Lake with floating mats of Water fern (Azolla sp.) Tangled lignum (Duma florulenta) Reeds (Typha sp.) and Water primrose (Ludwigia peploides) Kerang, Victoria,...

Doug Gimesy / Aerial view of a section of Middle Reedy Lake with floating mats of Water fern (Azolla sp.) Tangled lignum (Duma florulenta) Reeds (Typha sp.) and Water primrose (Ludwigia peploides) Kerang, Victoria,...

Nigel Cattlin / Frog (Rana temporaria) with its head above the pond water surface covered in a floating fairy fern (Azolla filiculoides), Devon, England, UK. September.

Nick Upton / Pillwort (Pilularia globulifera) growing on the margins of a heathland pond once used for clay extraction. Nationally rare. Dorset, England, UK, July.

Nick Upton / Pillwort (Pilularia globulifera) growing on the margins of a heathland pond once used for clay extraction. Nationally rare. Dorset, England, UK, July.