Potamogeton acutifolius 1 NE of Bjäresjö, Skåne 8108 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton acutifolius 2 Dakstas (Ryzas), Lithuania 100713 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton acutifolius 3 Dakstas (Ryzas), Lithuania 100713 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton acutifolius x compressus 1 S of Höjer, Jylland DK 140803 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton acutifolius x compressus 3 S of Höjer, Jylland DK 140803 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton acutifolius x compressus 4 S of Höjer, Jylland DK 140803 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton acutifolius x compressus 5 S of Höjer, Jylland DK 140803 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton acutifolius x compressus 6 S of Höjer, Jylland DK 140803 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton alpinus 1 S of Skjern, Jylland DK 140801 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton alpinus 2 S of Skjern, Jylland DK 140801 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton alpinus 3 S of Skjern, Jylland DK 140801 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton alpinus 4 S of Skjern, Jylland DK 140801 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton alpinus Lohärad, Uppland 060812 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton berchtoldii 1 Kallinge, Blekinge 150920 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton berchtoldii 10 Kallinge, Blekinge 150920 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton berchtoldii 2 Kallinge, Blekinge 150920 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton berchtoldii 3 Kallinge, Blekinge 150920 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton berchtoldii 4 Kallinge, Blekinge 150920 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton berchtoldii 5 Kallinge, Blekinge 150920 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton berchtoldii 6 Kallinge, Blekinge 150920 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton berchtoldii 7 Kallinge, Blekinge 150920 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton berchtoldii mouth of river Mörrumsån, Blekinge 950729 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton berchtoldii ssp groenlandicus near Kangerlussuaq, Greenland 140712 - Photo: (© 2014 Jan Thomas Johansson).

Potamogeton cf lucens x natans 1 Skjern Å, Sönderfelding, Jylland DK 130629 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton cf lucens x natans 2 Skjern Å, Sönderfelding, Jylland DK 130629 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton cf lucens x natans 3 Skjern Å, Sönderfelding, Jylland DK 130629 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton cf lucens x natans 4 Skjern Å, Sönderfelding, Jylland DK 130629 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton cf lucens x natans 5 Skjern Å, Sönderfelding, Jylland DK 130629 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton cf lucens x natans 6 Skjern Å, Sönderfelding, Jylland DK 130629 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton cheesemannii (together with Aponogeton distachyos) Baring Head SE of Wellington NZ 151115 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton coloratus 1 Botes Källmyr, Lojsta, Gotland 140830 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton coloratus 1 E of Nors, Bunge, Gotland 830626 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton coloratus 10 Tofta, Gotland 140830 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton coloratus 11 Tofta, Gotland 140830 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton coloratus 2 Botes Källmyr, Lojsta, Gotland 140830 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton coloratus 2 E of Nors, Bunge, Gotland 830626 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton coloratus 3 Botes Källmyr, Lojsta, Gotland 140830 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton coloratus 6 Botes Källmyr, Lojsta, Gotland 140830 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton coloratus 8 Tofta, Gotland 140830 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton coloratus 9 Tofta, Gotland 140830 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton compressus 1 NE of Svaneholm, Norra Åsum, Skåne 960911 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton compressus 2 NE of Svaneholm, Norra Åsum, Skåne 960911 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton crispus 1 (cult) Stångby, Skåne 040802 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton crispus 2 (cult) Stångby, Skåne 040802 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton crispus 3 Simrishamn Sk 190629 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton crispus 5 Simrishamn Sk 190629 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton crispus 6 Simrishamn Sk 190629 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton friesii 1 Råbelövssjön, Råbelöv, Skåne 820702 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton gramineus 4 Kvinnsgröta, Gräsgård, Öland 150606 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton gramineus 5 Kvinnsgröta, Gräsgård, Öland 150606 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton gramineus Stigtomta, Bälsta, Södermanland 030723 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton lucens 1 S of Höjer, Jylland DK 140803 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton lucens 2 S of Höjer, Jylland DK 140803 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton lucens Roslags-Bro, Uppland 980629 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton natans 1 Rösjön, Sollentuna, Uppland 040712 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton nodosus 6 near Merkine, Lithuania 150806 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton nodosus 7 near Merkine, Lithuania 150806 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton obtusifolius 1 northeasternmost part of Anten, Loo, Västergötland 140727 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton obtusifolius 2 northeasternmost part of Anten, Loo, Västergötland 140727 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton obtusifolius 3 northeasternmost part of Anten, Loo, Västergötland 140727 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton obtusifolius 5 northeasternmost part of Anten, Loo, Västergötland 140727 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton obtusifolius 7 northeasternmost part of Anten, Loo, Västergötland 140727 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton obtusifolius mouth of river Mörrumsån, Blekinge 950729 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton perfoliatus 1 Norr Malma, Uppland 980704 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton perfoliatus 2 Sollentuna, Uppland 970810 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton polygonifolius 1 Trosavik S of Stavanger, Norway 050805 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton polygonifolius 2 Trosavik S of Stavanger, Norway 050805 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton polygonifolius 3 Garinish Island, West Cork, Ireland 170524 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton polygonifolius 4 Garinish Island, West Cork, Ireland 170524 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton praelongus Malsta, Uppland 980709 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton pusillus 2 Kettinge, Lolland DK 190704 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton pusillus 6 Kettinge, Lolland DK 190704 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton pusillus 7 Kettinge, Lolland DK 190704 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton pusillus 8 Kettinge, Lolland DK 190704 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton pusillus 9 Kettinge, Lolland DK 190704 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton rutilus 1 Svaneholm, Norra Åsum, Skåne 040813 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton rutilus 2 Svaneholm, Norra Åsum, Skåne 040813 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton rutilus 3 Svaneholm, Norra Åsum, Skåne 040813 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton trichoides 1 fruit, Tågarp, Ö. Tomarp Sk, august 1930, coll. U. Sylvén (LD) - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton trichoides 3 fruits, Gärsnäs, Ö. Herrestad Sk, july 1935, coll. G. Björnström (LD) - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton acutifolius x compressus 2 S of Höjer, Jylland DK 140803 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton alpinus 5 S of Skjern, Jylland DK 140801 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton alpinus 6 S of Skjern, Jylland DK 140801 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton alpinus 7 S of Skjern, Jylland DK 140801 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton alpinus 8 S of Skjern, Jylland DK 140801 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton alpinus 9 S of Skjern, Jylland DK 140801 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton berchtoldii 8 Kallinge, Blekinge 150920 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton berchtoldii 9 Kallinge, Blekinge 150920 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton coloratus 12 Tofta, Gotland 140830 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton coloratus 13 Tofta, Gotland 140830 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton coloratus 4 Botes Källmyr, Lojsta, Gotland 140830 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton coloratus 5 Botes Källmyr, Lojsta, Gotland 140830 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton coloratus 7 Botes Källmyr, Lojsta, Gotland 140830 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton crispus 4 Simrishamn Sk 190629 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton crispus 7 Simrishamn Sk 190629 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton crispus 8 Simrishamn Sk 190629 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton crispus 9 Simrishamn Sk 190629 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton friesii 2 Degeberga, Skåne 930613 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton gramineus 1 Kvinnsgröta, Gräsgård, Öland 150606 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton gramineus 2 Kvinnsgröta, Gräsgård, Öland 150606 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton gramineus 3 Kvinnsgröta, Gräsgård, Öland 150606 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton lucens 1 Lake Ruzas SE of Dukstas, Lithuania 150804 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton lucens 2 Lake Ruzas SE of Dukstas, Lithuania 150804 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton lucens 3 Lake Ruzas SE of Dukstas, Lithuania 150804 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton lucens 4 Lake Ruzas SE of Dukstas, Lithuania 150804 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton lucens 5 Lake Ruzas SE of Dukstas, Lithuania 150804 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton lucens 6 Lake Ruzas SE of Dukstas, Lithuania 150804 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton lucens 7 Lake Ruzas SE of Dukstas, Lithuania 150804 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton natans 2 Rösjön, Sollentuna, Uppland 040712 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton nodosus 1 estuary of Evros, Greece 060607 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton nodosus 10 near Merkine, Lithuania 150806 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton nodosus 11 near Merkine, Lithuania 150806 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton nodosus 2 estuary of Evros, Greece 060607 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton nodosus 3 estuary of Evros, Greece 060607 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton nodosus 4 estuary of Evros, Greece 060607 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton nodosus 5 near Merkine, Lithuania 150806 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton nodosus 8 near Merkine, Lithuania 150806 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton nodosus 9 near Merkine, Lithuania 150806 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton obtusifolius 4 northeasternmost part of Anten, Loo, Västergötland 140727 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton obtusifolius 6 northeasternmost part of Anten, Loo, Västergötland 140727 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton pusillus 1 Kettinge, Lolland DK 190704 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton pusillus 3 Kettinge, Lolland DK 190704 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton pusillus 4 Kettinge, Lolland DK 190704 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton pusillus 5 Kettinge, Lolland DK 190704 - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).

Potamogeton trichoides 2 fruit, Tågarp, Ö. Tomarp Sk, august 1930, coll. U. Sylvén (LD) - Photo: Jan Thomas Johansson (© 2014 Jan Thomas Johansson).