Abstract
Invasive plants are nonnative to a region and can outcompete native plants, causing ecological harm.
Rhamnus frangula
L. is an invasive shrub in the United States, although cultivars are still commonly used for landscaping purposes, especially in the Midwest. The fecundity of the
R. frangula
cultivars ‘Columnaris’ Tall Hedge (TH), ‘Ron Williams’ Fine Line
®
(RW), Advanced Line 1 (AL1), and Advanced Line 2 (AL2) was evaluated through fruit production, seed production, seed size, and germination rates. Fruit was collected from these cultivars planted outdoors in the ground, and seeds were cleaned from the fruits. Seed germination was conducted under intermittent mist over 9 weeks. Over the 2 years of fruit collection, the three narrow-leaved cultivars (RW, AL1, and AL2) had greatly reduced fruit and seed production compared with TH. The RW, AL1, and AL2 cultivars produced an average of 79.1, 3.63, and 0.63 fruits, respectively, and 167.0, 6.75, and 1.00 seeds, respectively, per shrub in a year. Seed size was significantly smaller for RW and AL1 compared with TH, and RW also had a lower germination rate than TH. The low seed production of the narrow-leaved cultivars compared with TH suggests that these cultivars would be a better choice for landscaping use because they are less likely to produce large seed crops which could establish invasive populations. The reduced seed size and germination rate of RW in comparison with TH further suggests a lower invasive potential, as seeds are less likely to germinate and establish. Overall, the
R. frangula
cultivars, RW, AL1, and AL2 may be less likely than TH to contribute to invasiveness.