Effect of Seed Position on Parental Plant of <i>Kroenleinia grusonii</i> (Hildm.) Lodé. and <i>Echinocactus platyacanthus</i> Link &amp; Otto on Seed Germination at High Temperatures

ABSTRACT The position in which seeds develop on the parental plant can have effects on their physical and physiological characteristics. The current global temperature increase may affect these characteristics. The hypothesis was that seeds at the apex of the crown of Kroenleinia grusonii (Hildm.) Lodé. and Echinocactus platyacanthus Link &amp; Otto plants differ in size, viability, dormancy and germination, at six temperatures, from 20°C to 45°C, from those at the periphery of the crown. Our evaluations included the seed dimensions, mass, viability, and vigor, and seed imbibition and germination at constant temperatures. The seeds at the apex of the crown of K. grusonii plants were longer, heavier, and had more vigor and also significantly higher germination regardless of temperature than those from the periphery. Seeds at the apex of the crown of E. platyacanthus plants were less heavy and wide, but longer than those of the periphery. Seed dormancy, greater than 80%, in both species was eliminated by mechanical scarification. Diversity in physical and physiological characteristics of a seed cohort likely increases dispersal success and survival in the natural climate, accommodating to some extent the distribution of plant species with temperature changes due to global warming.