The Ilex (holly) is the largest woody dioecious angiosperm genus in Aquifoliaceae, comprising more than 700 trees and shrubs (Galle 1997). Hollies are treasured in gardens and everyday life for their diverse forms, foliage, fruits, and adaptability to different environments (Bailes and Andrews 2006).
Foster holly (I. ×attenuata) is a notable evergreen tree from the genus Ilex, resulting from the hybridization of I. cassine (Dahoon holly) × I. opaca (American holly). Of the five Foster hybrids, four are female (#1, 2, 3, and 5) and one is male (#4). Among these, ‘Foster #2’ is particularly commercially significant in the eastern United States and similar regions abroad. In 1964, a leaf color mutation of ‘Foster #2’ was discovered at the US National Arboretum and named ‘Sunny Foster’ (Cook 1993; Galle 1997; Fig. 1). Esteemed for its colorful leaves, fruits, robust vigor, cold hardiness, and ease of cultivation, ‘Sunny Foster’ received the Holly Society of America’s “Holly of the Year” award in 2006 (Holly Society of America 2006). It has gained widespread popularity and been extensively planted (Deng and Zhang 2021; DVeil 2015). Its red fruits and golden leaves cast enchanting reflections, further enhancing its appeal in China, where red and yellow are revered colors in traditional culture, making it a top industry standard holly in the Chinese market (Zhou et al. 2023).
Development of the I. ×attenuata ‘Jingshan Princess’.
Citation: HortScience 59, 9; 10.21273/HORTSCI17999-24
The leaf phenotypes of Ilex species display remarkable diversity in shape, texture, size, color, and margins, enhancing their commercial value and facilitating germplasm identification (Chong et al. 2022). Hollies with smooth-edged or dentate and serrate leaf margins are popular in China, especially for home gardening, whereas thorny varieties are less favored. This preference is driven by aesthetic considerations and market potential (Li 2021; Liu 2013). In landscaping, only a few spineless holly species or cultivars such as I. cornuta ‘Burfordii’, I. crenata, I. rotunda, and I. verticillata are preferred (Wu et al. 2020a, 2020b; Tang 2020). This preference underscores the cultural resonance of spineless foliage, symbolizing harmony, tranquility, and safety in our society (Zhu 2022).
Understanding the cultural importance and consumer interest in plants without thorns, the development of new thornless cultivars of I. ×attenuata could broaden market prospects and increase attractiveness to buyers, especially for residential gardening and city green spaces. The selection of I. ×attenuata ‘Jingshan Princess’ was based on its entire leaf margin, which retains the bright yellow color characteristic of its mother plant, enhancing its ornamental value. It also served as an excellent research material for studying leaf coloration and morphology (Chong et al. 2022; Zou et al. 2024). Furthermore, its round pyramidal habit, soil adaptability, and drought tolerance make it ideal for specimen planting, corners, and hedges. It is also well-suited for various landscape planting such as bonsai, topiary, backyard ornamentation, and structural accents. Its bright yellow leaves and potential red fruits are perfect for wreaths and other holiday decorations.
Origin
A leaf mutation lacking lateral spines was discovered on an I. ×attenuata ‘Sunny Foster’ plant at Hongming Zhang’s Garden in Jingshan (Hangzhou, China) by Hongming Zhang and Yiping Zou in 2016 (Fig. 1). Zou preserved the mutated branches through cutting propagation in autumn, obtaining additional clonal plants through subsequent propagation. After 8 years of semihardwood and hardwood cutting regeneration (2016–23) and 5 years of field observation (2019–23), the rooted stem cuttings maintained consistent morphological traits with the mother plant, confirming their phenotypic stability (Fig. 2). The asexual generations exhibited vigorous growth and flowering in the fourth year. Over the past 8 years, no significant pests or diseases have been observed.
Comparison of the new foliage, leaf phenotype, floral attributes, fruit characteristics, and habit between I. ×attenuata ‘Jingshan Princess’ (A–C) and ‘Sunny Foster’ (D–F). (A) New foliage of ‘Jingshan Princess’. (B) Flowers of ‘Jingshan Princess’. (C) Habit of ‘Jingshan Princess’. (D) New foliage of ‘Sunny Foster’. (E) Flowers and fruits of ‘Sunny Foster’. (F) Habit of ‘Sunny Foster’.
Citation: HortScience 59, 9; 10.21273/HORTSCI17999-24
Description
The distinctive features of ‘Jingshan Princess’ included its spineless leaves, golden-yellow new foliage, and round pyramidal habit (Fig. 2). ‘Jingshan Princess’ has been disseminated to holly enthusiasts, holly researchers and select nurseries for evaluation. Despite the original plant being relatively small, favorable feedback from growers had prompted its registration and ongoing propagation. The morphological descriptions are presented as the following:
Habit.
Evergreen with relatively loosely branches compared with ‘Sunny Foster,’ forming a round pyramidal, upright large shrub to small tree. The clones, which were 8 years old, were a small shrub, 1.5 m tall with a spread of 1.0 m.
Foliage.
The leaves of ‘Jingshan Princess’ are alternate, simple, smooth, coriaceous, and glabrous. The leaf blades are 4 to 5 cm long by 1.5 to 2 cm wide and are elliptic to obvate-elliptic, petioles 5 to 10 mm, with margins entire, spinless, slightly twisted. The leaf apex is acuminate, with a small mucronate tip spine of 2 mm, whereas the bases are obtuse to cuneate. Leaf color is brilliant yellow, Yellow Group 10A above and Yellow Group 11B on the underside (Royal Horticultural Society 2007; Fig. 1).
Flower.
The flowers are female, small (5 mm in diameter), borne in the leaf axils with 1 to 3 flowers in a cluster on the current year’s branches. Each flower features four obovate-oblong petals that are 2.5 to 3.0 mm in length and 1.2 to 1.5 mm in width, and slightly connate at the base. Inside the petals are four sterile stamens measuring 1.5 to 2.0 mm and a pistil (Fig. 2B). Flowering begins in late April, marking an early start to the holly flowering season.
Fruit.
Starting in the fourth year, ‘Jingshan Princess’ flowered and produced fruits annually. However, due to the absence of potential male plants in our planting area, the fruits did not mature and eventually dropped off. Therefore, it requires a nearby male Foster holly, American holly, or Dahoon holly for pollination and fruit set. If provided with these suitable pollination partners, it will bear red fruits similar to ‘Sunny Foster’ (Fig. 2E). The fruits of ‘Sunny Foster’ are vivid red (RHS 44A), ellipsoid, and measure 8 mm in length and 7 to 8 mm in diameter (Galle 1997).
Propagation
‘Jingshan Princess’ is primarily propagated through cuttings. Roots easily form on semihardwood to hardwood cuttings taken between August and October, extending to December if provided with 25 °C (77 °F) bottom heat. Healthy branches from the current year are selected and cut into 6 to 10 cm long segments, retaining 2 to 3 leaves at the top.
A mixture of peatmoss (Pindstrup Mosebrug A/S, Ryomgaard, Denmark) and perlite (Pinhui, Shouguang, China) (1:3, v:v) has proven to be an effective propagation substrate. The cuttings are treated with 1000 to 3000 mg·L−1 of potassium salt of indole-3-butyric acid (K-IBA; Bomei, Hefei, China) via a quick dip of 10 to 15 s. They are then inserted into the substrate and maintained under moderate humidity with sprinkler irrigation. This method results in rooting percentages of 90% within 6 to 8 weeks. Cuttings collected in late March before budbreak also root well, achieving rooting percentages of 80%.
Cultivation
This female variety thrives in full sun to partial shade, with its yellow leaves exhibiting more intense coloration under full sunlight. ‘Jingshan Princess’ is adaptable to a wide range of soil types and prefers a soil pH of 5.5 to 7.5, with 6.0 being ideal. Well-drained soil is essential for its growth. The cultivar demonstrated some tolerance to urban pollution and can survive in USDA hardiness zones 6 to 9 (US Department of Agriculture–Agricultural Research Service 2012). Minimal pruning is required to maintain its excellent shape, and it is relatively free from major pests and diseases.
Availability
Voucher specimens are on deposit in the Nanjing Forestry University Ilex Germplasm Resource Bank with the deposit number DIN0005. Cuttings are available for restricted trials for those interested in this new cultivar. Contact Yiping Zou (e-mail: yiping200889@126.com) for further information.
References Cited
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