Betula albosinensis 1 Copenhagen Bot Garden 130516 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula alleghaniensis 1 Lund Bot Garden 140430 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula chinensis 1 Copenhagen Bot Garden 160504 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula humilis 2 Torasoo, Rapla, Estonia 100718 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula humilis 3 Torasoo, Rapla, Estonia 100718 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula humilis 4 Torasoo, Rapla, Estonia 100718 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula lutea Storrs, Connecticut 900528 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula michauxii 1 Göteborg Bot Garden 130524 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula michauxii 2 Göteborg Bot Garden 130524 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula michauxii 3 Göteborg Bot Garden 130524 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula nana 1 Ulfshult, Örkened, Skåne 820709 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula nana 10 Lake Ferguson, Kangerlussuaq, Greenland 140701 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula nana 11 Lake Ferguson, Kangerlussuaq, Greenland 140701 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula nana 12 Store Saltsö, Kangerlussuaq, Greenland 140701 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula nana 13 Store Saltsö, Kangerlussuaq, Greenland 140701 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula nana 14 Store Saltsö, Kangerlussuaq, Greenland 140701 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula nana 15 Store Saltsö, Kangerlussuaq, Greenland 140701 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula nana 3 Todalen, Svalbard 790715 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula nana 4 Todalen, Svalbard 790715 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula nana 5 Kangerlussuaq, Greenland 140628 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula nana 6 Kangerlussuaq, Greenland 140628 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula nana 7 Kangerlussuaq, Greenland 140628 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula nana 8 Kangerlussuaq, Greenland 140628 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula nana 9 Lake Ferguson, Kangerlussuaq, Greenland 140701 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula nana x pubescens ssp czerepanovii 2 Vårstigen, Dovre, Norway 820804 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula pendula 1 Lund Sk 130919 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula pendula 2 Lund Sk 130919 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula pendula 3 Lund Sk 130919 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula pendula, Betula pubescens Höllviken, Skåne 030630 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula platyphylla var japonica Copenhagen Bot Garden 120919 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula populifolia Storrs, Connecticut 900528 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula pubescens 1 Höllviken Sk 130608 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula pubescens 2 Höllviken Sk 130901 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula pubescens 5 Höllviken Sk 130608 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula pubescens 6 Höllviken Sk 130608 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula 1a Flinck's Garden, Bjuv Sk 140518 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula 1b Flinck's Garden, Bjuv Sk 140518 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula 1c Flinck's Garden, Bjuv Sk 140518 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula albosinensis 2 Copenhagen Bot Garden 130516 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula albosinensis 3 Copenhagen Bot Garden 130516 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula albosinensis 4 Copenhagen Bot Garden 130516 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula albosinensis 5 Copenhagen Bot Garden 130516 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula alleghaniensis 2 Lund Bot Garden 140430 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula alleghaniensis 3 Lund Bot Garden 140430 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula alleghaniensis 4 Lund Bot Garden 140430 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula chinensis 2 Copenhagen Bot Garden 160504 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula humilis 1 Torasoo, Rapla, Estonia 100718 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula humilis 5 Torasoo, Rapla, Estonia 100718 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula michauxii 4 Göteborg Bot Garden 130524 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula nana 2 Ulfshult, Örkened, Skåne 820709 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula nana x pubescens ssp czerepanovii 1 Jotunheimen Fjellstue, Norway 820730 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula pendula 10 Lund Sk 130503 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula pendula 4 Lund Sk 130503 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula pendula 5 Lund Sk 130503 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula pendula 6 Lund Sk 130503 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula pendula 7 Lund Sk 130503 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula pendula 8 Lund Sk 130504 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula pendula 9 Lund Sk 130503 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula pendula f dalekarlica Ornässtugan, Dalarne 930718 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula pubescens 3 Höllviken, Skåne 950429 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Betula pubescens 4 Höllviken, Skåne 950429 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).