Morphophysiological dormancy in seeds of three eastern North American Sanicula species (Apiaceae subf. Saniculoideae): evolutionary implications for dormancy break

Abstract

Dormancy breaking and germination requirements were determined for seeds of the eastern North American (eNA) species Sanicula canadensis, Sanicula gregaria and Sanicula trifoliata, and the data compared to those available for the European–Asian (EurA) congener Sanicula europaea. Seeds of the three eNA species had underdeveloped embryos that were physiologically dormant, i.e., morphophysiological dormancy (MPD). Warm (25/15°C) followed by cold (5/1°C) stratification was effective in breaking dormancy in 100% of the S. canadensis seeds, but in only 29.3% of S. gregaria seeds and 43.3% of S. trifoliata seeds. Cold stratification alone broke dormancy in 38.7, 12.0 and 0% of S. canadensis, S. gregaria and S. trifoliata seeds, respectively. Thus, some seeds of S. canadensis and of S. gregaria that germinated have non-deep complex MPD, and others have deep complex MPD. All seeds of S. trifoliata that germinated have non-deep complex MPD. Within a phylogenetic context, the kind (level) of MPD may or may not differ between eNA Sanicula sister species because conspecific variation in the kind of MPD exists in seeds of S. canadensis and S. gregaria. Similarly, the kind of MPD in seeds of eNA S. canadensis and S. gregaria may or may not differ with the deep complex MPD in seeds of the EurA S. europaea. However, the non-deep complex MPD in all seeds of eNA S. trifoliata and deep complex MPD in seeds of S. europaea represent a distinct difference in this trait between two of the five clades comprising the genus Sanicula.