Pyrus zhaoxuanii is described as a new species from Guangdong Province, China, within the genus Pyrus, specifically under P. subg. Pashia. Although it shares morphological similarities with P. calleryana, P. zhaoxuanii can be distinguished by its uniquely small, obovate, leathery leaves, which have an obtuse apex and short petioles. A phylogenetic analysis based on single nucleotide polymorphisms (SNPs) indicated that P. zhaoxuanii forms an independent branch within Pyrus and is categorized in the Oriental clade, P. subg. Pashia. Currently, this species has only been recorded in the Danxiashan National Nature Reserve. Considering its potential distribution and population size, we recommend classifying this species as Least Concern (LC) according to the IUCN Red List classifications and criteria.

Danxia landscape, new species, phylogeny, Pyrus

The genus Pyrus L. belongs to the apple tribe Maleae in the Rosaceae family (Zhang et al. 2017; Liu et al. 2020a, 2022; Wang et al. 2024). Currently, at least 25 confirmed species of Pyrus have been identified worldwide, with 14 species recorded in China (Gu and Spongberg 2003; Jin et al. 2024a). As one of the most important fruit trees, pears have a cultivation history spanning possibly 3,000 years (Pu and Wang 1963; Teng 2011). Pyrus species exhibit self-incompatibility, necessitating cross-pollination from different flowers, which increases genetic heterozygosity among individual plants. Interspecific hybridization is common within Pyrus, leading to a blend of genes and extensive genetic variation among species (Jin et al. 2024b). This frequent introgression is prevalent in the apple tribe Maleae, including apples, pears, and their relatives (Phipps et al. 1991; Lo and Donoghue 2012; Liu et al. 2019, 2020b, 2023; Jin et al. 2023). This genetic complexity complicates determining relationships between different Pyrus species (Westwood and Bjornstad 1971), making their classification particularly challenging. Furthermore, many geographical subspecies have historically been regarded as “species” (Westwood and Challice 1978).

Pyrus calleryana Decne., commonly known as Callery pear, is native to eastern and southern China, Korea, and Japan (Bell and Zimmerman 1990; Gu and Spongberg 2003) and is frequently used as a rootstock for pear trees. The Flora of China recognizes four varieties of P. calleryana: P. calleryana var. calleryana, P. calleryana var. integrifolia T.T.Yu, P. calleryana var. koehnei (C.K.Schneid.) T.T.Yu, and P. calleryana var. lanceolata Rehder (Gu and Spongberg 2003).

To clarify the classification of the genus Pyrus, a previous study examined the diversity of Pyrus and the independent domestication of Asian and European pears (Wu et al. 2018). This study analyzed 113 individuals and constructed a phylogenetic tree of major Pyrus species, categorizing them into Asian and European pears, resulting in six distinct groups. Among these, P. calleryana, P. pashia Buch.-Ham. ex D.Don, and P. betulifolia Bunge were classified as Asian pear Group II, indicating their close phylogenetic relationships. These three species exhibit relatively limited domestication and share characteristics of small, undomesticated fruits. Building on this research, an updated infrageneric classification divided pears into two subgenera: P. subg. Pashia (Asian pears) and P. subg. Pyrus (European pears) (Jin et al. 2024a). All members of Group II fall under P. subg. Pashia.

During our investigation in Danxiashan Mountain, we found two types of Callery pear (P. calleryana) with different morphological characteristics. Individuals on the gentle slopes at the foot of the mountain are consistent with the normal P. calleryana phenotype morphologically, while those on the steep slopes and cliffs exhibit distinct traits, including small, obovate, thick, leathery leaves with obtuse tips and short petioles. Additionally, some branchlets have evolved into thorns, and the plant’s stature has become shrubbier.

Initially, we hypothesized that these plants were ecotypes of P. calleryana. However, as our research progressed, it became clear that this plant should be classified under P. subg. Pashia as a new branch in the phylogenetic tree. Based on morphological characteristics and phylogenetic analyses, we propose that it represents a new species, which we describe and illustrate here.

A total of 1,164,026 SNPs were generated for the 32 samples. The phylogenetic tree inferred from these SNPs closely resembled findings from previous SNP-based research (Wu et al. 2018), defining five subclades with high support values (Fig. 2). Furthermore, our results also correspond with the ortholog-based phylogenomic studies (Jin et al. 2024a, 2024b). Those P. calleryana individuals we collected, along with its varieties, formed a sister group to the putative new species. Ultimately, the putative new species, P. calleryana, P. pashia, P. betulifolia, and P. pseudopashia, collectively formed Group 1, which showed high support values and belonged to the P. subg. Pashia (Jin et al. 2024a). This phylogenetic tree indicates that pronounced genetic differentiation exists between the new species and other species within Group 1.

Figure 2. 

Phylogenetic tree built based on SNPs, Malus pumila as the outgroup. Among them, those marked red are P. zhaoxuanii, and those marked blue are P. calleryana that we collected in Danxia Mountain. The numbers displayed on the diagram represent the bootstrap confidence level of the phylogenetic tree.

The putative new species is most similar to the Pyrus calleryana, both morphologically and molecularly. Both species possess small fruits, five white petals, and corymb inflorescences. However, compared to P. calleryana, the putative new species has smaller leaves (19–31 × 10–15 mm vs. 40–80 × 35–60 mm), obovate leaves (vs. broadly ovate or ovate, rarely narrowly elliptic), apex obtuse (vs. apex acuminate, rarely acute), shorter petioles (2–12 mm vs. 20–40 mm), distinct stem thorns (vs. nearly no stem thorns), and a shrubby habit (vs. tree habit) (Table 2).

Morphologically, a common characteristic of Group 1 in our study is small fruit size, which distinguishes them from other groups. Within Group 1, Pyrus zhaoxuanii differentiates from other species due to its small, obovate leaves. When we first encountered it at Mount Danxia, we suspected it was an ecotype of P. calleryana. However, P. zhaoxuanii has established a new branch on the phylogenetic tree based on SNP data. Molecular phylogenetics supports its classification as an independent species rather than an ecotype of P. calleryana.

Taxonomic treatment

 Pyrus zhaoxuanii X.W.Yi, B.B.Liu & Q.Fan, sp. nov.

urn:lsid:ipni.org:names:77359363-1

Figs 3, 4, 5, 6 Chinese name. 昭璇梨

Type.

China. • Guangdong Province, Shaoguan City, Danxiashan National Nature Reserve, 25°0'28.26"N, 113°39'42.80"E, alt. 380 m, 24 February 2024, Y.Y. Wu et al. DNPC4016 (holotype: SYS!; isotypes: SYS!, PE!).

Diagnose.

Pyrus zhaoxuanii is similar to P. calleryana, but can be differentiated by its small, obovate leaves, short petioles, pronounced stem thorns, and shrubby habit.

Description.

Deciduous shrubs or small trees, 2–5 m high, with lateral branches; bark dark gray to brownish with vertical splits; much-branched; Twigs smooth, spiny, covered with linear lenticels. Leaf buds long ellipsoid, with 5–7 hairy scales outside. Leaves fascicled on short branches; petiole 2–12 mm long; Leaf blade obovate, rarely elliptic, (14) 19–31 (45) × (7) 10–15 (23) mm, margin obtusely serrate, base cuneate, apex blunt or round, rarely acuminate, leathery in quality. Corymb 2–8 flowered, receptacle cup-shaped, covered with short hairs; sepals are triangular, ca. 4 mm long, woolly, with rust-colored velutinous on the margins, bending downwards at the apex; flower 12–17.5 (29.5) mm in diameter; Petals 5, 5–8 × 5–6 mm, pure white, glabrous, obovate, margin slightly sinuate, apex rounded; filament 3–7 mm long; anthers purple to pink; style 2, 4–6.5 mm long, glabrous; flower stalk (19) 21–35 mm long. Pome small, spheroid, reddish-brown to brownish-black, ca. 1 cm long; fruiting pedicel 18–36 mm long. Seeds ovate, blackish, ca. 2 × 5 mm.

Figure 3. 

Flower and pome of Pyrus zhaoxuanii A frontal dissection of the flower B stamens C longitudinal section of the flower D front view of the entire flower E cross and longitudinal sections of the fruit F cross-section of the ovary. Scale bars: 1 cm (A, E); 5 mm (B, C, D, F).

Phenology.

Flowering was observed from February to March, while fruiting occurred from September to October.

Etymology.

Pyrus zhaoxuanii is named in honor of Prof. Zhao-Xuan Zeng (1921–2007), a famous geographer of South China Normal University, who made significant contribution to the study of danxia landscape.

Figure 4. 

Pyrus zhaoxuanii A plant, stem with many branches and thorn B habitat, growing on the edge of cliffs or steep slopes C branches with many subdivisions and thorns D lenticels on young branches E surface of the stem F, G leaves during the fruiting period H, I leaf buds and bud scales with hair J, K flowers L, M fruits I comparison of P. zhaoxuanii and P. calleryana (left: P. zhaoxuanii, right: P. calleryana).

Distribution and habitat.

The new species is currently known only from its type locality, Mount Danxiashan, Renhua County, Guangdong Province, China. It typically grows on steep slopes at altitudes of 200–600 m above sea level.

Conservation status.

The new species is a common shrub found on the steep slopes of Mount Danxia. Most individuals are located within the Danxia Nature Reserve, which is well protected, and we observed no active threats or ongoing declines in population size. According to the Guidelines for Using the IUCN Red List Categories and Criteria, v. 16 (IUCN Standards and Petitions Committee 2024), we suggest classifying P. zhaoxuanii as Least Concern(LC).

Figure 5. 

Line drawing of Pyrus zhaoxuanii A flowering plant B fruiting plant C flower D appearance of fruit E leaf F pistil G longitudinal section of flower H longitudinal and cross section of fruit I bud scales J stamens. Scale bars: 5 cm (A, B); 1 cm (C, D, E, F, G); 2 cm (H); 2 mm (I); 5 mm (J). Illustrated by Si-Rui Pan.

Additional specimens examined

(Paratypes): China. • Guangdong Province, Shaoguan City, Danxiashan National Nature Reserve, 113°39'50.56"N, 25°0'27.81"E, alt. 328 m, 24 February 2024, Y.Y. Wu et al. DNPC4014 (SYS!); China. • Guangdong Province, Shaoguan City, Danxiashan National Nature Reserve, 24°58'28.73"N, 113°44'10.29"E, alt. 285 m, 26 September 2023, Y.Y. Wu & Q. Fan 102 (SYS!).

Figure 6. 

Holotype of Pyrus zhaoxuanii, Y.Y. Wu et al. DNPC4016 (SYS).

We are grateful to the Guangdong Danxiashan National Nature Reserve for their support in collecting all materials. Our appreciation extends to Li-Juan Liao and Chu-Hui Zhang for their assistance in fieldwork. We would like to express our heartfelt thanks to the Biological Museum of Sun Yat-sen University for their help with specimen preparation and binding. Additionally, we greatly appreciate the assistance provided by Si-Rui Pan in the illustration.