For Pycnanthemum
Chambers, H. 1993. Chromosome survey and analysis of artificial hybrids in Pycnanthemum. Castanea 58: 197-208.
Chambers, H., and J. Hamer. 1992. More about picky Pycnanthemums; can taxonomy be practical after all? Tipularia 7: 19-24.
Grant, E., and C. Epling. 1943. A study of Pycnanthemum (Labiatae). Univ. of Calif. Publ. in Botany 20: 195-240.
Harley et al. 2004. In Kadereit, J.W. 2004. The families and genera of vascular plants. VII. Flowering plants – Dicotyledons – Lamiales (except Acanthaceae including Avicenniaceae). Springer, Berlin. 478 pp.
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