2018 ASHS Annual Conference

North American shrubs in the genus Ptelea (Rutaceae) have unfulfilled potential to increase the diversity of managed landscapes and to support populations of pollinators and swallowtail butterflies. White flowers of Ptelea are highly fragrant, and pistillate flowers give rise to clusters of distinctive samaras. Vague information on how to optimize germination of seeds of Ptelea trifoliata, and no recommendations for P. crenulata, prompted us to investigate effects of cold (4 ˚C) stratification periods of 0, 4, 8, 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). Eight and 16 weeks of stratification led to 89% and 100% germination, respectfully, for P. crenulata, and to 73% and 91% germination, respectively, for P. trifoliata; shorter periods of stratification resulted in lower germination percentages for both species. Germination value, a measure of speed and uniformity of germination, was higher for seeds of P. crenulata stratified for 16 weeks and for seeds of P. trifoliata stratified for 8 and 16 weeks than germination value of seeds treated with shorter stratification periods. Peak day, germination distribution, and mean daily germination of the two species did not differ, nor did stratification period affect these measures. All values were calculated based on the number of viable seeds, which was determined with tetrazolium tests on ungerminated seeds. About half of the seeds of both species were not viable. Propagators seeking to grow these two species of Ptelea from seed should cold-stratify the seeds for 16 weeks.