References

For Gratiola

Estes, D., and R.L. Small. 2007. Two new species of Gratiola (Plantaginaceae) from eastern North America and an updated circumscription for Gratiola neglecta. J. Bot. Res. Inst. Texas 1: 149-170. Google Scholar

Estes, D., and R.L. Small. 2008. Phylogenetic relationships of the monotypic genus Amphianthus (Plantaginaceae tribe Gratioleae) inferred from chloroplast DNA sequences. Systematic Bot. 33: 176-182. Google Scholar

Freeman, C.C. 2019b. Gratiola. In Flora of North America Editorial Committee. 2019. Flora of North America north of Mexico. Volume 17, Magnoliophyta: Tetrachondraceae to Orobanchaceae. Oxford Univ. Press, New York, NY. 737 pp. Google Scholar

Pennell, F.W. 1935. The Scrophulariaceae of eastern temperate North America. Academy of Natural Sciences of Philadelphia Monograph No. 1. Google Scholar