Northern Prairie Wildlife Research Center
2. Sparganium emersum Rehm.
Our representatives are assigned to var. multipedunculatum (Morong) Rydb.
The distinctions between this entity, S. chlorocarpum and S. angustifolium
Michx. are far from clear. The latter is generally separated from the other
two by its floating-leaved habit, smaller pistillate heads 1-2 cm in diameter
and shorter fruit beaks 0.5-2 mm long. S. emersum in many respects
seems to represent an intermediate between S. angustifolium and S.
chlorocarpum, yet the latter two appear quite distinct where they are
sympatric in eastern North America and where S. emersum is supposedly
absent. Until this complex is studied in greater detail, we have the unsatisfactory
situation of relying too heavily on geographical criteria for separating S.
chlorocarpum and S. emersum with the latter being the western North
American counterpart of the former.