Within angiosperms, the genus Ilex L. (Aquifoliaceae) is the largest group of woody plants with separate male and female individuals, boasting more than 600 species. These species are found primarily in the tropical and subtropical areas of South America and Asia (Loizeau et al. 2016; Yao et al. 2022; Zhou et al. 2022). The germplasms include evergreen and deciduous types, growing as trees or shrubs. Most people cultivate them because of their economical benefits and visually appealing attributes.
Approximately one tenth of the species are used in the preparation of beverages (Loizeau et al. 2016), as exemplified by Paraguayan tea (maté tea) made from the leaves of Ilex paraguariensis A. St.-Hil. in South America (Bracesco et al. 2011); Black Drink “Cassena” in North America, which is derived from the leaves of Ilex vomitoria Aiton (Folch 2024); and Kudingcha in Asia, which is made from the leaves of Ilex latifolia Thunb. (Gan et al. 2018).
Certain species and variations serve as popular ornamental plants in parks and gardens. Branches bearing red fruit commonly serve as Christmas decorations in European and North American regions (Xu et al. 2025).
Although taxa in the genus Ilex are highly diverse, their flowers and fruit are quite similar in morphology, unlike their leaves, which show great variation in texture, color, shape, size, and serrations (Yao et al. 2016). These differences play an important role in distinguishing different Ilex germplasms (Chong et al. 2022). For example, Ilex ×dabieshanensis ‘Ning Qing 1’ stands out with its leathery leaf texture, broadly ovate leaf shape, and shiny, blackish green leaf color (Zhou et al. 2023); I. ×dabieshanensis ‘Ning Qing 2’ is characterized by its dwarf tree habit, small leaf size, and serrated leaf margins (Chen et al. 2024); and I. ×dabieshanensis ‘Ning Qing 3’ is distinctive for its unique, oblong leaf morphology (Chong et al. 2023).
Ilex dabieshanensis ‘Zi Lin’ was introduced by the Institute of Botany, Jiangsu Province and Chinese Academy of Sciences (Nanjing Botanical Garden Memorial Sun Yat-Sen). This cultivar has garnered significant attention for its leathery leaf texture, serrated leaf margins, and red-purple young branches and fruit, greatly enriching the diversity of the Ilex germplasm. So far, no serious pests or diseases have been noted, enhancing its appeal as a garden or landscape highlight.
Origin
Ilex ×dabieshanensis K. Yao & M. B. Deng is a species native to the Dabie Mountains of western Anhui, China. In Spring 2014, hybridization work was carried out using the parents of I. dabieshanensis (♀) and I. latifolia (♂) at the repository of Ilex spp. germplasm of Nanjing Botanical Garden Memorial Sun Yat-Sen, Jiangsu, China (lat. 32°03′N, long. 118°49′E). In total, more than 500 cross-pollinated seeds were collected in winter and then stored in moist (∼20%) sand to break seed dormancy. In Spring 2015, all the seeds were sown in a mixed substrate of peat, rice chaff ash, and perlite (∼2:2:1 by volume). After germination, the seedlings were transplanted into a field with a 30-× 30-cm spacing. In May 2017, an individual plant with a leathery leaf texture, serrated leaf margins, young red-purple branches, and brownish green young leaves was observed and selected for further evaluation, ultimately receiving the name ‘Zi Lin’. After 4 years of semihardwood/hardwood stem cutting (2018–21) and 6 years of field observation (2019–24), the plants resulting from clonal propagation exhibited morphological characteristics consistent with the mother plant, confirming their phenotypic stability. Notably, they grew vigorously in Jiangsu (similar to US Department of Agriculture plant hardiness zones 8b and 9a) and could tolerate high (37 to 41 °C) and low (–8 to 0 °C) temperatures, with only a few incidence of leaf spots observed. In 2024, the cultivar was authorized by the Forest Variety Certification Committee of China.
Description
Among the current Ilex germplasm resources, ‘Zi Lin’ most resembles ‘Ning Qing 4’, which was also released by the Institute of Botany, Jiangsu Province and Chinese Academy of Sciences in 2023. ‘Ning Qing 4’ has young light-green branches [Royal Horticultural Society (RHS) 142B] (Royal Horticultural Society 2015) and leaves (RHS 142A), whereas ‘Zi Lin’ has young red-purple (RHS 60A) branches and young brownish green (RHS 152C) leaves. The color of young fruit is yellowish green (RHS 145A) in ‘Ning Qing 4’, but is red-purple (RHS 71A) for ‘Zi Lin’ (Table 1; Fig. 1). The specific characteristics of ‘Zi Lin’ are described in the following sections.
Comparison of phenotypic attributes between Ilex × ‘Ning Qing 4’ and Ilex × ‘Zi Lin’.
Comparison of phenotypic attributes between Ilex × ‘Ning Qing 4’ (Fig. 1A and C) and Ilex × ‘Zi Lin’ (Fig. 1B and D).
Citation: HortScience 60, 7; 10.21273/HORTSCI18626-25
Habit.
The evergreen plant has an ellipsoidal canopy, which can grow up to 1.5 m in height, with a spread of 0.7 m at 9 years of age (Fig. 2A).
Phenotypic characteristics of Ilex × ‘Zi Lin’. (A) Evergreen plant with an ellipsoidal canopy. (B) Young brownish green [Royal Horticultural Society (RHS) 152C] (Royal Horticultural Society 2015) leaves and young red-purple (RHS 60A) branches. (C) Young red-purple (RHS 71A) fruit. (D) Red (RHS 43A), circular mature fruit with discoid stigmas.
Citation: HortScience 60, 7; 10.21273/HORTSCI18626-25
Branches and foliage.
The young branches are red-purple (RHS 60A), whereas the mature ones are light green (RHS 144B), with a diameter of 2.65 to 2.82 mm. No lenticels are observed on the surfaces, and the internode length is 1.1 to 2.4 cm. Although the young leaves are brownish green (RHS 152C), they differ from the mature leaves, which are leathery and medium green (RHS NN137A). Mature leaf blades are elliptical (6.0–7.8 cm in length and 2.8–3.5 cm in width) and moderately curled, and are attached to petioles that are 1.0 to 1.2 cm in length. The leaf bases are cuneate and the apexes are acuminate. Leaf veins are visible on the surface, but are not prominently pronounced. The serrations around the leaf margins have a shallow depth and density (Fig. 2B).
Flowers.
The cyme produces 6 to 10 small, greenish yellow (RHS 151A) flowers, which are axillary and placed discreetly on the current year's branchlets. Each flower features four obovate–oblong petals measuring 3.7 to 3.8 mm in length and 1.8 to 2.0 mm in width, and are slightly fused at the base. Within the petals, there is a prominent pistil surrounded by four degenerated stamens. In Jiangsu Province, the plant starts to bloom in early April, with a flowering duration of ∼2 weeks.
Fruit.
The tree produces an abundance of fruit that remain until late winter. These medium-size fruit (0.6–0.8 cm in vertical diameter and 0.7–0.9 cm in horizontal diameter) are circular in shape and usually mature by late October. The young fruit are red-purple (RHS 71A) (Fig. 2C), and then they turn red (RHS 43A) after 5 months, with persistent discoid stigmas (Fig. 2D).
Propagation
‘Zi Lin’ is propagated mainly by semihardwood stem cuttings (June to July in Jiangsu) or hardwood stem cuttings (late November to late March, before sprouting). For semihardwood cuttings, the current year’s semilignified branches should be selected and then cut into short lengths (∼5–8 cm) with two to three half leaves. For hardwood cuttings, thick, healthy, first-year annual growth should be selected and then cut into 8- to 12-cm lengths. The cutting depth for ‘Zi Lin’ is ∼3 to 5 cm. To boost survival rates, 2000 ppm indole-3-butyric acid can be used to dip the cuttings for 8 to 10 s in advance. During the process, sprinkler irrigation is suggested to keep a moderate and constant humidity. In general, > 90% of the cuttings will root within 30 d.
Cultivation and Application
‘Zi Lin’ thrives in full sun and can also tolerate a semishade environment. Acidic soil is ideal for its cultivation. During early spring, plants should be transplanted with sufficient soil for the root zone and with adequate moisture. Because of its slow growth, minimal pruning is needed. Growth can be enhanced significantly by timely drainage and fertilizer application during the winter and spring rainy seasons. So far, only a few leaf spot incidences have been observed, and there are no major concerns about pests or diseases. ‘Zi Lin’ is suitable for courtyard beautification, street trees, public gardens, and other theme attraction construction.
Availability
The cultivar Zi Lin is available through Dr. Chen Hong at the Institute of Botany, Jiangsu Province and the Chinese Academy of Sciences (Nanjing Botanical Garden Mem. Sun Yat-Sen).
References Cited
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