A classification system for germination in desiccation-sensitive Fagaceae acorns: with particular focus on physiological and epicotyl dormancy

Abstract

Abstract Since the 17th century, understanding the germination ecology of Fagaceae fruits has attracted considerable interest. However, several questions remain, including: (i) How widespread is the coexistence of dormancy and desiccation-sensitivity (DS)? (ii) What kind of dormancy do Fagaceae fruits/acorns have? (iii) How common is epicotyl dormancy in Fagaceae fruits/acorns? (iv) What is the influence of embryonic axis position in Fagaceae fruits/acorns in relation to germination? Our literature synthesis shows that most—but not all—Fagaceae fruits/acorns are desiccation-sensitive. Many Quercus species have either physiological dormancy (PD) or epicotyl physiological dormancy (ePD), though the latter has been hitherto underestimated. Here, we propose a new classification system for Fagaceae species and identify two germination types: Type-I and Type-II. Further, we subdivide Type-I into Type-IA adjacent lingular (radicle extends through the apex and shoots develop close to the fruits/acorns) and Type-IS adjacent lingular (radicle extends near the scar and shoots develop close to the fruits/acorns), and Type-II into Type-IIA remote tubular, where the radicle extends through the apex or near the scar (Type-IIS), but shoots emerge at a distance from the fruits/acorns. Why the embryonic axis position varies between species cannot be explained based on phylogenetic relationships.