Jessica D. Lubell

Detecting the influence of ornamental Berberis thunbergii var. atropurpurea in invasive populations of Berberis thunbergii (Berberidaceae) using AFLP1.

Japanese barberry (Berberis thunbergii DC.) is a widespread invasive plant that remains an important landscape shrub represented by ornamental, purple-leaved forms of the botanical variety atropurpurea. These forms differ greatly in appearance from feral plants, bringing into question whether they contribute to invasive populations or whether the invasions represent self-sustaining populations derived from the initial introduction of the species in the late 19th century. In this study we used amplified fragment length polymorphism (AFLP) markers to determine whether genetic contributions from B. t. var. atropurpurea are found within naturalized Japanese barberry populations in southern New England. Bayesian clustering of AFLP genotypes and principal coordinate analysis distinguished B. t. var. atropurpurea genotypes from 85 plants representing five invasive populations. While a single feral plant resembled B. t. var. atropurpurea phenotypically and fell within the same genetic cluster, all other naturalized plants sampled were genetically distinct from the purple-leaved genotypes. Seven plants from two different sites possessed morphology consistent with Berberis vulgaris (common barberry) or B. ×ottawensis (B. thunbergii × B. vulgaris). Genetic analysis placed these plants in two clusters separate from B. thunbergii. Although the Bayesian analysis indicated some introgression of B. t. var. atropurpurea and B. vulgaris, these genotypes have had limited influence on extant feral populations of B. thunbergii.

Fecundity of Japanese Barberry (Berberis thunbergii) Cultivars and Their Ability to Invade a Deciduous Woodland

Abstract Japanese barberry is an important landscape shrub that has a demonstrated potential to be invasive in ∼30 states across the central and northern United States. Forty-six cultivars were evaluated for their potential to produce fruits and seeds in a randomized, replicated field planting. Seeds from a subset of cultivars were evaluated for their ability to germinate and survive as seedlings in a deciduous woodland. Seed production for cultivars varied from no seeds to more than 12,000 seeds plant−1 and the number of seeds per fruit ranged from 0.1 to 1.8. Five cultivars produced fewer than 100 seeds plant−1, and two cultivars failed to produce fruit. When plants were allowed to mature for 4 to 5 yr beyond the first evaluation time, cultivars exhibited significant increases in fruits per plant, producing as much as 35,000 fruits plant−1 (‘Sparkle’). ‘Golden Devine’ and ‘Red Chief’, fruitless cultivars at the first evaluation, produced 165 and 20 fruit plant−1, respectively, at the follow-up evaluation, demonstrating that long-term evaluation of cultivars is necessary to accurately assess sterility. Between 12.5 and 31% cultivar seed sown in a deciduous woodland germinated, and seedlings survived at rates between 5.6 and 29.3%. Coupling cultivar seed-production data with germination and survival data in a deciduous woodland suggests that even cultivars producing as few as 100 seeds annually have the potential to contribute a few seedlings each year to a natural area. Nomenclature: Japanese barberry, Berberis thunbergii DC Management Implications: Japanese barberry cultivars represent a substantial economic value to the nursery and landscape industries because they are popular, durable plants, widely used for landscaping. Unfortunately, Japanese barberry is also an invasive plant, and some states have imposed laws preventing the propagation and sale of the species and all cultivars. Cultivars of Japanese barberry look and behave differently from the species, with many being dwarf forms with purple or yellow foliage. The dramatic visual differences between cultivars of Japanese barberry and the species have led some to suggest that certain cultivars may be noninvasive or have a lower potential for rapid establishment in natural communities and could be exempted from species bans. The objective of this study was to evaluate the fecundity of a wide range of commercially available Japanese barberry cultivars to determine whether any could be considered noninvasive. We determined fruit production, seed production, and germination rates for 46 cultivars of Japanese barberry and its hybrids. Using seed from a representative subset of cultivars, we also determined the potential each cultivar had to germinate, survive, and grow in a deciduous woodland. Cultivars varied considerably in their seed production from more than 12,000 seeds to no seeds, and several cultivars produced fewer than 100 seeds plant−1. When plants were allowed to mature for 4 to 5 yr beyond the first evaluation time, cultivars exhibited significant increases in fruits per plant. ‘Sparkle’ produced more than 35,000 fruits plant−1 and ‘Golden Devine’ and ‘Red Chief’, which initially appeared to be fruitless, produced 165 and 20 fruit plant−1, respectively. To accurately assess reproductive potential of cultivars, it is necessary to conduct evaluations for durations that are longer than those typically reported and to provide ample opportunities for cross-pollination. Cultivar seed germination rates were between 12.5 and 31% in a deciduous woodland, and seedlings survived at rates between 5.6 and 29.3%. By combining seed production data with establishment data in a deciduous woodland, even cultivars producing as few as 100 seeds yr−1 in the landscape have the potential to contribute a few seedlings each year to a natural area. Most barberry cultivars clearly cannot be considered noninvasive, and even those that are the least fecund, can still be minimally invasive if they reach an age of 10 yr or more.

Production of Three Eastern U.S. Native Shrubs: Effects of Auxin Concentration on Rooting and Shade Level on Container Plant Growth

American fly honeysuckle (Lonicera canadensis), hobblebush (Viburnum lantanoides), and sweetbells (Eubotrys racemosa) are eastern U.S. native shrubs with ornamental value, which might become successful nursery crops if they propagate readily from stem cuttings and grow uniformly in containers. We evaluated rooting success for hobblebush and sweetbells using stem cuttings treated with indole-3butyric acid (IBA) in talc at concentrations of 0, 1000, 3000, or 8000 ppm. For hobblebush, IBA at 1000, 3000, or 8000 ppm will yield 70% rooting success. For sweetbells, IBA treatment did not enhance rooting, and 88% rooting success can be achieved with untreated cuttings. Stem cuttings of american fly honeysuckle root at 49% (previously published). We also evaluated all three native shrubs grown in nursery trade #1 containers under shade levels of 0%, 40%, or 70%. American fly honeysuckle grown under 40% or 70% shade were larger, had a greener hue angle, and higher chlorophyll fluorescence (Fv/Fm) than plants grown in full sun. Throughout the study period, Fv/Fm values for full-sun american fly honeysuckle were 0.6 or below, indicating plants were stressed. Hobblebush in 40% and 70% shade were wider, had more leaves, and enhanced foliage color compared with fullsun plants. Hobblebush in 70% had the highest Fv/Fm values at 0.78 or higher across the study period. For sweetbells, plant width increased as shade level increased. Even though sweetbells in 70% shade were wider and larger, they lacked density and had a less appealing habit than 40% shade and full-sun plants. Of the three study species, sweetbells might be the easiest plant for growers to incorporate into production because it propagates readily from stem cuttings and can be grown in full sun to 40% shade. Hobblebush and american fly honeysuckle may present more challenges for growers because hobblebush requires considerable shade to grow and american fly honeysuckle is more difficult to propagate.