Cold acclimation and deacclimation of Ptelea and Zanthoxylum (Rutaceae)

Abstract

The North American genera Ptelea L. and Zanthoxylum L. are distributed farther north than most other genera in the Rutaceae (citrus family). We used 3 methods to characterize cold acclimation and deacclimation of common hoptree (Ptelea trifoliata L.) and common pricklyash (Zanthoxylum americanum Mill.), species with potential to diversify landscapes. Female and male common hoptrees were compared, and we contextualized our results by measuring cold hardiness of western hoptree (Ptelea crenulata Greene) and representatives of other woody genera of the order Sapindales that are hardy in the Upper Midwestern US: maple (Acer L.), ailanthus (Ailanthus Desf.), corktree (Phellodendron Rupr.), and sumac (Rhus L.). A discoloration method was ineffective, so we assessed hardiness based on electrolyte leakage and the reduction of 2,3,5-triphenyltetrazolium chloride (TTC). TTC reduction indicated that Ptelea and Zanthoxylum were more cold-hardy than indicated by electrolyte leakage. Western hoptree, sampled in its native habitat, was the least hardy. Maximal hardiness of common hoptree, common pricklyash, and western hoptree was –42, –33, and –21 °C (–44, –27, and –6 °F), respectively. Hardiness of female and male common hoptrees did not differ consistently. While common hoptree and common pricklyash have been considered hardy to Zone 3, our assessments of plants from a portion of the species’ geographic ranges indicate common hoptree is the more cold-hardy species.