Sparganium sp; Bur-reeds are true water plants with grass-like leaves which are either fully submerged or (partially) floating on the surface of the water. The inflorescences and fruits however, rise above the water-level. On Iceland 3 species occur, being:
Sparganium hyperboreum (Northern Bur-reed)
Sparganium natans (Least Busr-reed)
Sparganium angustifolium (Floating Bur-reed)
The three species are difficult to tell apart. The best differentiating characteristic is the shape of the fruits:
Sp. hyperboreum (Northern Bur-reed) has no beak on top of the single fruits
Sp. natans (Least Busr-reed) has a very short beak
Sp. angustifolium (Floating Bur-reed) has long beaks.
However the first two species hybridise..... (to make things even more complicated). Sparganium hyperboreum is the most wide-spread of all bur-reeds while Sparganium angustifolium is considered to be rather rare.
Sparganium species (Bur-reeds) are members of the Bur-reed family (Sparganiaceae).