Plants of Iceland: Potamogeton alpinus, Red Pondweed, Fjallnykra

Potamogeton alpinus; the Red Pondweed is a common pondweed on Iceland. This plant grows submerged in ponds and lakes. On Iceland there are a few more Potageton species growing in ponds, lakes, waterways. They can be differentiated by their leaf-shapes. One has to take into account that submerged leaves and floating leaves can differ. The following table describes the leaf shapes of Icelandic Potamogeton species and closely related species of the pondweed family:

Species name	Submerged leaf-shape	Floating leaf-shape	Status
P. gramineus	sessile, sharply pointed top rather narrow	Broader with long leaf stalks. Also pointed leaf apexes	In ponds and lakes all around Iceland
P alpinus	leaves tapering to the base with obtuse apex's	usually absent, if present similar to P. gramineus	Common
P. natans	absent	rather broad elliptic shaped. Also pointed leaf apexes	Rather rare
P. perfoliatus	Sessile short/broad leaves	Absent	Rather rare: prefers relative warmer conditons
P. praelongus	Long sessile leaves. Not tapering to the base, almost clasping stems	absent	Rather rare
P. berchtoldii	Linear leaves	absent	Not uncommon
Stuckenia filiformis	Thread-shaped leaves	absent	Differs from Potamogeton species in having a serie of flower bundles along the flowering stems. Common, also in interior highland ponds
Zanichellia palustris	short gras-like thread-shaped leaves	absent	Inflorescences in leaf-axils composed of just one male eand female flower. Rare
Ruppia maritima	Thread-like	absent	brackish and saline conditions. Individual flowers long-stalked. These stalks spirally coil at fruiting stage.

Alas I do not have pictures yest of all Potamogetonaceae (pondweed family) members.

Potamogeton_alpinus / red pondweed is a member of the pondweed family (Potamogetonaceae). The Icelandic name of the Alternate Water-milfoil is Fjallnykra.