Evaluation location: Minnesota, United States
Wild collected seed from 17 populations were grown and represented the latitudinal range of the species from Tennessee, Mississippi, and Florida. In 2018, seed from each maternal parent was surface-sown onto a soilless germination mix (Sungrow Horticulture, Agawam, MA). In the greenhouse, flats were placed on heat mats (Hydrofarm Horticulture, Petaluma, CA) and covered with clear plastic domes to maintain high relative humidity. Greenhouse temperatures were maintained between 25 and 30°C with natural daylength. After germination, seedlings were transplanted into 7.62-cm square pots holding a soilless potting medium (Sungrow Horticulture, Agawam, MA) and grown in the greenhouse until May. Seedlings were transplanted into 186.7-cm3 square pots with peat:pine bark (1:1) potting mix and transferred to an outdoor container nursery with overhead irrigation. Plants were watered as needed throughout the growing season. A minimum of 100 random seedlings from each population were evaluated after terminal buds had set at the end of the growing season. Because plants were completely randomized within the container nursery, random sampling was achieved by measuring the first 100 seedlings located in each population. Plants were measured from the top of the soil to the top of the apical bud on the tallest shoot, and nodes were counted on the same shoots. Internode length was estimated by dividing the total height by the number of nodes. See citation for additional details.