Glossary of "Life (9th ed.)" by Sadava et al. (2011)
- A protective surface structure. In Gymnosperms and angiosperms, a layer of tissue around the ovule which will become the seed coat.
Glossary of Plant Systematics (1st ed.) by Simpson (2006)
- A sheath or flap of tissue that surrounds the megasporangium (nucellus) of an ovule and develops into the seed coat of the seed.
Glossary of "The Evolution of Plants (2nd ed.)" by Willis & McElwain (2014)
- Outermost layer of tissue covering the ovule that develops into the seed coat.
- Sadava, D., Hillis, D. M., Heller, H. C. & Berenbaum, M. R. 2011. Life: The Science of Biology, 9th ed. -xliv + 1266 pp. Sinauer Associates, Inc., Sunderland.
- Simpson, M. G. 2006. Plant Systematics. -xi + 590 pp. Elsevier Academic Press, Oxford.
- Willis, K. J. & McElwain, J. C. 2014. The Evolution of Plants, 2nd ed. -ix + 398 pp. Oxford University Press, Oxford.