All tropical African material was earlier classified as C. stagnalis Scop., but recent taxonomic work has shown that several species can be recognized based on morphological, pollen and chromosomal differences.
Submerged plants often have lanceolate or linear leaves and long internodes, while in plants where the shoots reach the surface the internodes tend to be shorter and have rosettes of elliptic or spathulate leaves
In pollen, the exine surface shows the Croton pattern, which is a reticulate pattern with processes (clavae) at the intersections of the walls (muri) (Erdtman, G., 1952, Pollen morphology and plant taxonomy: Angiosperms, p. 173)
'Flora of China @ eFloras (2008). Published on the Internet http://www.efloras.org/flora_page.aspx?flora_id=2 [accessed August 2016]' Missouri Botanical Garden, St. Louis, MO & Harvard University Herbaria, Cambridge, MA.
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