Cold Stratification and Pericarp Removal Improve Seed Germination of Ptelea trifoliata and Ptelea crenulata

Abstract

Two species of North American shrubs in the genus Ptelea (Rutaceae), commonly known as eastern and western hoptree or wafer ash, have unfulfilled potential to increase the diversity of managed landscapes and support populations of pollinators and swallowtail butterflies. The white flowers of Ptelea are highly fragrant, and pistillate flowers give rise to clusters of distinctive samaras. The insufficiency of information about improving germination of seeds of Ptelea trifoliata and lack of recommendations for Ptelea crenulata prompted us to investigate effects of pericarp removal and cold (4 °C) stratification periods of 0, 4, 8, and 16 weeks on the germination of seeds of these two species. Samaras were collected from multiple plants of both species in the midwestern United States (P. trifoliata) and California (P. crenulata). The germination percentage of viable seeds, calculated after tests of viability with tetrazolium chloride of seeds that did not germinate, increased with longer stratification periods, with 100% germination for P. crenulata and 91% germination for P. trifoliata after 16 weeks of stratification. The germination value, a measure of the speed and uniformity of germination, and peak value also increased with longer stratification in both species. Pericarp removal increased the germination percentage of both species and increased the peak and germination value of P. crenulata. Propagators seeking to grow these species of Ptelea from seed should remove the pericarp and cold-stratify seeds for 16 weeks to improve germination success.