Nick Upton / Female Eurasian beaver (Castor fiber) and five kits feeding on a Willow (Salix) sapling, River Otter, Devon, England, UK, July. Part of Devon Wildlife Trust's Devon Beaver Trial.

Andres M. Dominguez / Bacteria (Lepthotryx discophora) causing iridescent patterns and White willow tree leaf (Salix alba) in river, Sierra de Grazalema Natural Park, southern Spain, November.

Jussi Murtosaari / Garden warbler (Sylvia borin), catching flies in willow tree, Korpoo, Uto, Finland, May.

Gerrit Vyn / Muskox (Ovibos moschatus) feeding on willows. North Slope, Alaska. September.

Sven Zacek / Misty lake, with trees reflected in the water, and Willow (Salix) trees silhouetted on the shore, Suur Emajogi river, Tartumaa, Estonia, May 2014.

Ernie Janes / Blue tit (Cyanistes caeruleus) hanging on Pussy willow branch, Norfolk, England, UK, April.

Alex Hyde / Peacock butterfly (Inachis io) feeding on Goat Willow catkins (Salix caprea), an important food source for pollinators in early spring. Peak District National Park, UK. April.

Nick Upton / Eurasian beaver (Castor fiber) gnawing the trunk of a Willow tree (Salix sp.) in woodland enclosure at night. Devon Beaver Project, run by Devon Wildlife Trust, Devon, UK, April. Taken by a remote cam...

Ammonite / Mining bee (Andrena apicata) flying and feeding from Sallow (Salix caprea) catkins, with pollen sacs on hind legs, France, March.

Theo Bosboom / Reed and Willows (Salix sp) with hoarfrost, Weerribben-Wieden National Park, the Netherlands, December 2007

Terry Whittaker / 2020VISION / Water vole (Arvicola amphibius / Arvicola terrestris) feeding amongst vegetation, Kent, England, UK, February. 2020VISION Exhibition. 2020VISION Book Plate. Did you know? The character 'Ratty' from Ke...

Orsolya Haarberg / Flowering willows (Salix sp.) in midges (Chironomus islandicus) swarming. Mývatn, Iceland. June 2008

Andy Sands / Blue tit (Parus caeruleus) perched among Pussy willows, West Sussex, England, UK

Terry Whittaker / Grey Heron ( Ardea cinerea) perched, Amsterdam, Netherlands. April.

SCOTLAND: The Big Picture / Downy willow (Salix lapponum) saplings to be used in habitat restoration. Trees for Life nursery, Dundreggan Conservation Estate, Dumfries and Galloway, Scotland, UK.

Nick Upton / Female Eurasian beaver (Castor fiber) feeding from a felled Willow tree (Salix) with kit, River Otter, Devon, England, UK, June.

Sven Zacek / European elk (Alces alces), three standing together near frost covered Willow (Salix sp) bushes with Suur Emajogi River beyond. Alam-Pedja Nature Reserve, Tartumaa, Southern Estonia. January 2011.

Andy Sands / Goat wIllow (Salix caprea) Young male catkins often known as pussy willow, Hertfordshire, England, UK, April

Andy Sands / Grey willow (Salix cinerea) close up of male flowers, Hertfordshire, England, UK, April, Focus Stacked

Mike Read / Goat willow (Salix caprea) catkins and new leaves. Blashford Lakes Nature Reserve, Hampshire and Isle of Wight Wildlife Trust Reserve, Ellingham, Ringwood, Hampshire, England, UK. April.

Suzi Eszterhas / North American beaver (Castor canadensis) kit eating Willow (Salix sp). Martinez, California, USA. July.

Suzi Eszterhas / North American beaver (Castor canadensis) kit playing with Willow (Salix sp) at water's edge. Martinez, California, USA. June.

Suzi Eszterhas / North American beaver (Castor canadensis) eating Willow (Salix sp). Martinez, California, USA. June.

Erlend Haarberg / Great spotted woodpecker (Dendrocopus major) on a Goat willow (Salix caprea) Klaebu, Norway, September

Chris Mattison / Mountain willow (Salix arbuscula) male catkins. Cultivated plant.

David Woodfall / Mixed woodland of Oaks and Willows developing on fields of former wheat production.. Knepp Wildland Project, formerly intensive farmland now turned to conservation and sustainable farming. Horsham, We...

David Woodfall / Purple emperor butterfly (Apatura iris) male on Goat willow (Salix caprea). Knepp Wildland Project, formerly intensive farmland now turned to conservation and sustainable farming. Horsham, West Sussex...

Robert Thompson / Pussy willow (Salix sp), Brackagh Moss Portadown, County Armagh, Republic of Ireland. April.

Eric Medard / Common chiffchaff (Phylloscopus collybita) reaching down to water from willow branch, France. September.

Adrian Davies / Goat willow (Salix caprea) catkin shedding feathery seeds. Surrey, England, UK. May.

Adrian Davies / Goat willow (Salix caprea) catkin shedding feathery seed. Surrey, England, UK. May

Matthew Maran / Goat willow (Salix caprea) felled by a Eurasian beaver (Castor fiber) with teeth marks The riverside tree will resprout with new shoots supplying a source of food for the beavers for years to come. De...

Matthew Maran / Goat willow (Salix caprea) felled by a Eurasian beaver (Castor fiber). The riverside tree will resprout with new shoots supplying a source of food for the beavers for years to come. Devon, England, UK...

Olga Kamenskaya / Halberd willow (Salix hastata) in flower, Vaygach Island, Arctic, Russia, July

Nick Upton / Common osier (Salix viminalis) female catkins releasing seeds, Wiltshire, UK, April.

Nick Upton / Common osier (Salix viminalis) female catkins releasing seeds, Wiltshire, UK, April.

Michel Roggo / Red Ludwigia (Ludwigia sp.) in a clear stream of the Pantanal, Brazil. Photographed for The Freshwater Project

Michel Roggo / Water hyacinth (Eichhornia sp.) and red Ludwigia (Ludwigia sp.) in a clear stream of the Pantanal, Brazil. Photographed for The Freshwater Project

Michel Roggo / Water hyacinth (Eichhornia sp.) and red Ludwigia (Ludwigia sp.) in a clear stream of the Pantanal, Brazil. Photographed for The Freshwater Project

Michel Roggo / Red Ludwigia (Ludwigia sp.) in a clear stream of the Pantanal, Brazil. Photographed for The Freshwater Project

Michel Roggo / Water hyacinth (Eichhornia sp.) and red Ludwigia (Ludwigia sp.) in a clear stream of the Pantanal, Brazil. Photographed for The Freshwater Project

Michel Roggo / Water hyacinth (Eichhornia sp.) and red Ludwigia (Ludwigia sp.) in a clear stream of the Pantanal, Brazil. Photographed for The Freshwater Project.

Ashley Cooper / E.ON's biofuel power station in Lockerbie, Scotland with Willow trees (Salix sp,) planted as a biofuel crop. The power station is fuelled 100 by wood sourced from local woodlands and generates enough...

Ashley Cooper / Willow trees (Salix sp) planted as a biofuel crop at E.ON biofuel power station, Lockerbie, Scotland. The power station is fuelled by wood sourced from local woodlands and generates enough electricit...

Konrad Wothe / Tortoiseshell butterfly (Aglais urticae) on pussy willow (Salix caprea) flower, Bavaria, Germany, March.

David Kjaer / Whitethroat (Sylvia communis) male perched on Willow branch in spring, Wiltshire, England, UK, April.

Michel Roggo / Water hyacinth (Eichhornia sp.) and red Ludwigia (Ludwigia sp.) in clear stream, Pantanal, Brazil. Photographed for The Freshwater Project.

Michel Roggo / Red Ludwigia (Ludwigia sp.) in a clear stream, Pantanal, Brazil. Photographed for The Freshwater Project