Villarreal, J. C., D. C. Cargill, A. Hagborg, L. Soderstrom, and K. S. Renzaglia. “A Synthesis of Hornwort Diversity: Patterns, Causes and Future Work”. Phytotaxa, vol. 9, no. 1, Sept. 2014, pp. 150-66, doi:10.11646/phytotaxa.9.1.8.