False reports of physical dormancy in seeds of gymnosperms and angiosperms

Abstract

Eighteen families of angiosperms but no families of gymnosperms have been documented anatomically (palisade layer of macrosclereids with a light line and a water gap in the seed coat or endocarp – physical dormancy [PY] syndrome) and/or physiologically (imbibition tests of scarified versus nonscarified seeds) to contain species with PY. However, a literature review revealed that 76 families of angiosperms and 5 families of gymnosperms have been reported to have PY. Also, PY was wrongly reported in some genera of Anacardiaceae and Cucurbitaceae, which do have some genera with true PY. In none of the reports of PY was water-impermeability of the seed coat properly documented by seed covering layer anatomy or imbibition tests. Furthermore, other studies on the same or related species falsely reported to have PY found that seeds of 78.3% of the species had physiological dormancy, 19.1% morphophysiological dormancy and 2.6% nondormant seeds. We conclude that reports of PY for species in the 81 families of extant seed plants are incorrect and that the correct number of families with PY is still 18. False reports of PY could have negative implications for studies on understanding the relationship between kinds of dormancy and the ecology, evolution and biogeography of seed plants by distorting the dormancy profile.