Glossary of "Plant Biology (1st ed.)" by Graham et al. (2003)
- The outermost tissues of a plant; the epidermis or the periderm (of woody plants).
Glossary of Plant Systematics (1st ed.) by Simpson (2006)
- The outer region of plant organs, composed of the epidermis.
- Graham, L. E., Graham, J. M. & Wilcox, L. W. 2003. Plant Biology. -xxxv + 497 pp. Pearson Education, Inc., Upper Saddle River.
- Simpson, M. G. 2006. Plant Systematics. -xi + 590 pp. Elsevier Academic Press, Oxford.