Polygonum argyrocoleon 5 Copenhagen Bot Garden 140719 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum aviculare 10 Eagle Gorge Nat. Park, Georgia 170425 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum aviculare 11 Eagle Gorge Nat. Park, Georgia 170425 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum aviculare 12 Eagle Gorge Nat. Park, Georgia 170425 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum aviculare 2 Ljunghusen, Stora Hammar Sk 130804 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum aviculare 3 Lund Sk 120713 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum aviculare 4 Lund Sk 120713 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum aviculare 5 Lund Sk 120713 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum aviculare 6 Ljunghusen, Stora Hammar Sk 130804 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum aviculare 7 Lund Sk 120713 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum aviculare 8 Lund Sk 120713 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum aviculare 9 Lund Sk 120713 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum cognatum 1 Bergianska 060620 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum cognatum 2 Bergianska 060620 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum filicaule 1 Napa Hai, Yunnan 110709 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum filicaule 2 Napa Hai, Yunnan 110709 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum maritimum 1 Akr. Kastellou, Karpathos, Greece 040521 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum maritimum 2 S of Pefkochori, Greece 050529 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum oxyspermum 1 Irevik, Hangvar, Gotland 140829 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum oxyspermum 10 Irevik, Hangvar, Gotland 140829 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum oxyspermum 11 Irevik, Hangvar, Gotland 140829 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum oxyspermum 12 Irevik, Hangvar, Gotland 140829 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum oxyspermum 13 Irevik, Hangvar, Gotland 140829 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum oxyspermum 14 Irevik, Hangvar, Gotland 140829 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum oxyspermum 15 Irevik, Hangvar, Gotland 140829 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum oxyspermum 16 Irevik, Hangvar, Gotland 140829 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum oxyspermum 17 Irevik, Hangvar, Gotland 140829 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum oxyspermum 18 Irevik, Hangvar, Gotland 140829 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum oxyspermum 2 Irevik, Hangvar, Gotland 140829 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum oxyspermum 3 Irevik, Hangvar, Gotland 140829 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum oxyspermum 4 Irevik, Hangvar, Gotland 140829 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum oxyspermum 5 Irevik, Hangvar, Gotland 140829 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum oxyspermum 6 Irevik, Hangvar, Gotland 140829 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum oxyspermum 8 Irevik, Hangvar, Gotland 140829 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum oxyspermum 9 Irevik, Hangvar, Gotland 140829 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum raii ssp norvegicum 1 Dverberg, Andöya, Norway 810801 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum raii ssp norvegicum 2 Dverberg, Andöya, Norway 810801 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum argyrocoleon 1 Copenhagen Bot Garden 140719 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum argyrocoleon 2 Copenhagen Bot Garden 140719 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum argyrocoleon 3 Copenhagen Bot Garden 140719 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum argyrocoleon 4 Copenhagen Bot Garden 140719 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum argyrocoleon 6 Copenhagen Bot Garden 140719 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum argyrocoleon 7 Copenhagen Bot Garden 140719 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum argyrocoleon 8 Copenhagen Bot Garden 140719 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum aviculare 1 Skanör Sk 130622 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum aviculare 13 Eagle Gorge Nat. Park, Georgia 170425 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Polygonum oxyspermum 7 Irevik, Hangvar, Gotland 140829 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).