References for AMAZONAS Magazine article:

6 Hornwort Species: genus Ceratophyllum

By Maike Wilstermann-Hildebrand
Amazonas English Edition, Vol. 5, Number 1, January/February 2016

Herendeen, P.S., D.H. Les, and D.L. Dilcher. 1990. Fossil Ceratophyllum (Ceratophyllaceae) from the Tertiary of North America. Amer J Bot 77 (1): 7–16.

Les, D.H. 1986. The Evolution of Achene Morphology in Ceratophyllum (Ceratophyllaceae), I. Fruit-Spine Variation and Relationships of C. demersum, C. submersum and C. apiculatum. Syst Bot 11 (4): 549–58.

———. 1988. The Evolution of Achene Morphology in Ceratophyllum (Ceratophyllaceae), II. Fruit Variation and Systematics of the “Spiny-Margined” Group. Syst Bot 13 (1): 73–86.

———. 1988. The Evolution of Achene Morphology in Ceratophyllum (Ceratophyllaceae), III. Relationship of the “Facially-Spined” Group. Syst Bot 13 (4): 509–18.

———. 1989. The Evolution of Achene Morphology in Ceratophyllum (Ceratophyllaceae), IV. Summary of Proposed Relationships and Evolutionary Trends. Syst Bot 14 (2): 254–62.

———. 1991. Genetic Diversity in the monoecious hydrophile Ceratophyllum (Ceratophyllaceae). Amer J Bot 78 (8): 1070–82.

Wilmot-Dear, M. 1985. Ceratophyllum revised—a study in fruit and leaf variation. Kew Bull 45: 243–71.