Sedum yongkangense (Crassulaceae), a New Species from Zhejiang, East China ^†

Abstract

In this paper, Sedum yongkangense is described as a new species based on morphological and molecular analyses, and its taxonomic relationships are discussed. Morphological analysis indicates S. yongkangense should be classified in the genus Sedum L. sect. Sedum and is distinct from the related species S. ryukyuense, S. mukojimense and S. boninense in having the morphology of a biennial life form; spreading cymes with numerous flowers; unequal, linear, terete sepals; horizontally spreading follicles; and an inland habitat. Molecular analysis of sequences of the nuclear ribosomal internal transcribed spacer (ITS) also demonstrates that S. yongkangense has a highest similarity of only 87.21% with any known species. Phylogenetic analyses indicate that S. yongkangense should be closely related to S. bulbiferum, but the latter differs in having the morphology of a perennial life form; a congested fertile stem; axillary bulbils of leaves; a spatulate-oblanceolate and flat leaf blade; lanceolate to oblanceolate and flat sepals; and deep yellow anthers and spreading follicles.

1. Introduction

Sedum Linnaeus (1753: 430) is the largest genus in the family Crassulaceae, with about 470 succulent herbaceous to (sub-)shrubby species (Thiede and Eggli 2007 [1]). Species within this genus are widely distributed in the Northern Hemisphere, and are most diverse in the Mediterranean region, Central America, the Himalayas, and East Asia (Stephenson 1994 [2]; Thiede and Eggli 2007 [1]). Sedum can be easily distinguished by its usually alternate leaves; sessile carpels slightly connate at the base; free, mostly yellow or white petals; and stamens in two whorls (Thiede and Eggli 2007 [1]). However, molecular studies have revealed that Sedum is a highly polyphyletic group (Nikulin et al., 2016 [3]), which may be due to the high morphological plasticity and variability within the genus (Carrillo-Reyes et al., 2009 [4]). In China, 121 species have been recorded in the Flora of China (Fu and Ohba 2001 [5]). During the past 20 years, about 18 Sedum species have been newly described from China (Huang et al., 2023 [6]).

During the preparation of the latest edition of the Flora of Zhejiang, a Province in southeastern China, botanical expeditions were conducted in Zhejiang and its neighboring regions, resulting in the first discovery of a previously unidentified Sedum species in April 2023; these plants grow on bare rocks at an elevation of 150–250 m in Yongkang City, Zhejiang. The species is similar to S. ryukyuense, S. mukojimense, S. boninense in linear, terete leaves. We investigated the distinctiveness of this unusual population via morphological and phylogenetic examination, and identified S. yongkangense as a new species which should be classified within S. sect. Sedum.

2. Materials and Methods

2.1. Field Work and Sampling

This species is endemic to Yongkang City, Zhejiang Province; it grows on sunny bare rock in low-altitude hills. We conducted field surveys of this species during the seedling, flowering, and fruiting periods, and collected four molecular samples and seventeen specimens, with four at different locations. To observe their growth process, we also transplanted some individuals into an artificially managed garden. We observed and measured the morphological features of 17 specimens using a Leica DFC320 stereomicroscope (Leica Microsystems, Wetzlar, Germany) and took microcolour photographs of seeds with a 10× microscope objective (Leica Microsystems, Wetzlar, Germany). A total of 16 characteristics were selected for comparison, and detailed differences among S. yongkangense, S. ryukyuense, S. mukojimense, S. boninense, and S. bulbiferum are listed in

Table 1. Main differences among Sedum yongkangense, S. ryukyuense, S. mukojimense, S. boninense, and S. bulbiferum.

Characteristics	S. yongkangense #	S. ryukyuense $	S. mukojimense *	S. boninense $,^	S. bulbiferum &,$
Life cycle	biennial	perennial	perennial	perennial	perennial
Bulbils	no	no	bulbs form underground after flowering	bulbs form underground after flowering	bulbils in leaf axils
Sterile stem	absent	present, 2–4 cm tall	absent	absent	absent
Fertile stem	solitary, herbaceous, erect, ca. 11 cm tall, Ф1–2 mm, branched near base	erect, 4–10 cm tall, branched near base	solitary, fleshy, 7–20 cm tall, base Ф3 mm, erect, sometimes branched	solitary, erect, 5–20 cm tall, branched upward	congested, 7–22 cm tall
Leaf blade	sparse, linear, terete, slightly flattened	densely, narrowly oblong or linear-spatulate, terete	densely, spatulate to obovate, flat	densely, narrowly elliptic or oblanceolate, terete	proximal stem leaves opposite; leaf blade ovate-spatulate. Distal stem leaves alternate; leaf blade spatulate-oblanceolate, flat
Leaf size	4–12 × 1–2.8 mm	3–6 × 1.5–2.5 mm	6–14 × 2–5 mm	5–16 × 1.5–4 mm	10–15 × 2–4 mm
Inflorescences	once trifurcate, secondary bifurcate, many flowers	solitary on branches	usually 1–12 flowers	usually 1–3 flowers	once trifurcate, secondary bifurcate, many flowers
Pedicel	sessile	sessile	sessile	short pedicellate	sessile
Sepals	unequal, fleshy, terete, linear, 4–6.5 × 1.1–1.3 mm, ascending at flowering	equal, fleshy, elliptic-lanceolate, ca. 2.5 mm long	equal, fleshy, narrowly elliptic or oblanceolate, 2–4 × 0.8–1.2 mm	equal, fleshy, narrowly elliptic or oblanceolate, ca. 3 mm long, ascending at flowering	unequal, lanceolate to oblanceolate, 3 – 4 × ca. 1 mm
Anthers	orange-red	orange-red	red	bright yellow	deep yellow
Ovules	8–14	unknown	unknown	4–6	10–16
Follicles	horizontal spreading	spreading	spreading	spreading	spreading
Seed surface	minutely pits in pale	unknown	unknown	unknown	minutely tuberculate
Seed size	0.68–0.76 × 0.37–0.43 mm	unknown	unknown	unknown	0.6 × 0.23 mm

Based on Fu and Ohba (2001) [5] ^&, Ohba, H. (2001) [7] ^$, Takuro Ito (2020) [8] *, Takasi Tuyama. (1936) [9] ^{^}, and own measurements at ZM ^#.

, based on Fu and Ohba (2001) [5], Ohba (2001) [7], Ito (2020) [8], Takasi Tuyama. (1936) [9], and our own measurements at ZM (Table 1). The voucher specimens were kept in the Herbarium of Zhejiang Museum of Natural History.

2.2. DNA Extraction and Sequencing

DNA was isolated from freshly collected leaves of the newly discovered species found in Yongkang City, Zhejiang Province, using the Tiangen plant genomic DNA extraction kit (Tiangen Biotech, Beijing, China). ITS primers ITS-A (5′-GGAAGGAGAAGTCGTAACAAGG-3′) and ITS-4 (5′-TCCTCCGCTTATTGATATGC-3′) amplifying ITS1, 5.8S rDNA, and ITS2 regions were taken from Blattner (1999) [10] and White et al. (1990) [11]. PCR program started with 5 min of initial denaturation at 94 °C, followed by 35 cycles of denaturation for 20 s at 98 °C, annealing for 30 s at 58 °C Tm for ITS, extension for 45 s at 68 °C, and final extension for 7 min at 68 °C with KODFX DNA Polymerase (KFX-101, TOYOBO, Osaka, Japan). The PCR products were analyzed using a 1.5% agarose TAE gel and subsequently sequenced by the Beijing Genomics Institute (Shenzhen, China). The newly generated sequences from this study were deposited in the National Center for Biotechnology Information (NCBI) (GenBank accessions: PP464048, PP464049, see Supplemental Table S1).

2.3. Data Analysis

To ascertain the phylogenetic position of the newly discovered species, DNA sequences of species in the genus Sedum, as well as additional outgroup species, were used. ITS sequences sourced from the NCBI website (Supplemental Table S1) were obtained for the purpose of constructing a phylogenetic tree with species from Eastern Asia in the Acre clade (Crassulaceae) (Nikulin et al., 2016 [3]; Messerschmid et al., 2020 [12]; Chai et al., 2024 [13]). A total of 73 sequences (including 3 outgroup species) were selected for subsequent analysis. SeqMan software 11.1.0 (Burland 2000 [14]) was utilized for the assembly and editing of complementary strands, and the sequence was aligned with MAFFT v7.505 (Katoh and Standley 2013 [15]) using the ‘-auto’ strategy and normal alignment mode. Gap sites were removed with trimAl v1.2rev57 (Capella-Gutiérrez et al., 2009 [16]) using the “-automated1” command. Phylogenetic analyses were based on a Bayesian approach using MrBayes 3.2.7a (Ronquist et al., 2012 [17]) and maximum-likelihood (ML) phylogenetic analysis using RAxML (Stamatakis 2014 [18]). In the Bayesian phylogenetic analysis, we used the GTR+I+G model (2 parallel runs, 1,000,000 generations), in which the initial 25% of sampled data were discarded as burn-in. Convergence of Bayesian Markov Chain Monte Carlo (MCMC) runs was assessed using three criteria: 1. Average standard deviation of split frequencies** between parallel runs (target < 0.05), which reached 0.021 after 1,000,000 generations (max 0.112 for individual splits). 2. Potential Scale Reduction Factor (PSRF) for branch lengths and parameters, averaging 1.005 (max 1.337). 3. Estimated Sample Size (ESS) for key parameters (TL = 359, alpha = 3415, pinvar = 4156), all exceeding 200. The ML phylogenetic analyses were implemented in RAxML 8 with a GTRGAMMA substitution model. The ML bootstrap proportions (BPs) and trees were obtained by simultaneously running rapid bootstrapping with 10,000 iterations followed by a search for the most likely tree.

3. Results

3.1. Morphological Analysis

After field observation, morphological characteristics of the new species were investigated and compared to those of the related species. The new species, named S. yongkangense, was found to be clearly different from the other related species (Figure 1; Table 1). It is mainly distinguished from them by its biennial life form; sparse, linear, terete, slightly flattened leaf blades; first-trifurcating, secondarily bifurcating inflorescence with many flowers; unequal, fleshy, terete, linear sepals; and its horizontally spreading follicles. The distinguishing characteristics of the new species and four relatives in the Acre clade are listed in detail in Table 1. Specifically, S. yongkangense differs from S. ryukyuense in having a biennial life form (vs. perennial); sparse, linear, slightly flattened leaves (vs. densely arranged, narrowly oblong or linear-spatulate leaves); first-trifurcating, secondarily bifurcating inflorescence with many flowers (vs. solitary on branches); unequal, fleshy, terete, linear sepals 4–6.5 × 1.1–1.3 mm (vs. equal, fleshy, elliptic-lanceolate sepals ca. 2.5 mm long); and horizontally spreading follicles (vs. spreading follicles); in particular, the inland habitat on sunny bare rock in low-altitude hills of S. yongkangense is a key difference from the island habitat on limestone rocks along the seacoast of S. ryukyuense. S. yongkangense differs from S. mukojimense in having a biennial life form (vs. perennial); it lacks bulbils (vs. having bulbs form underground after flowering); it has sparse, linear, terete, slightly flattened leaves 4–12 × 1–2.8 mm (vs. densely arranged, spatulate to obovate, flat leaves 6–14 × 2–5 mm), inflorescence: trifurcation and secondary bifurcation with many flowers (vs. usually 1–12 flowers), and unequal, fleshy, terete, linear sepals 4–6.5 × 1.1–1.3 mm (vs. equal, fleshy, narrowly elliptic or oblanceolate sepals 2–4 × 0.8–1.2 mm); and horizontally spreading follicle (vs. spreading follicles). Notably, the inland habitat of S. yongkangense contrasts with the island, coastal habitat of S. mukojimense. S. yongkangense differs from S. boninense in having a biennial life form (vs. perennial); inflorescence: trifurcating then bifurcating with many flowers (vs. usually 1–3 flowers); sessile (vs. short pedicellate); unequal, fleshy, terete, linear sepals 4–6.5 × 1.1–1.3 mm (vs. equal, fleshy, narrowly elliptic or oblanceolate sepals ca. 3 mm long); orange-red anthers (vs. bright yellow); ovules 8–14 (4–6); and horizontally spreading follicle (vs. spreading follicles). The inland habitat of S. yongkangense is a key difference from the island seacoast habitat of S. boninense. S. yongkangense differs from S. bulbiferum in having a biennial life form (vs. perennial); being without bulbils (vs. bulbils in leaf axils); having solitary fertile stems (vs. congested); solitary, herbaceous, erect stems ca. 11 cm tall and 1–2 mm in diameter (vs. congested, 7–22 cm hall); sparse, linear, terete, slightly flattened leaves 4–12 × 1–2.8 mm (vs. proximal stem leaves opposite; leaf blade ovate-spatulate, distal stem leaves alternate; leaf blade spatulate-oblanceolate, flat, 10–15 × 2–4 mm); unequal, fleshy, terete, linear sepals 4–6.5 × 1.1–1.3 mm (vs. unequal, lanceolate to oblanceolate, 3–4 × ca. 1 mm); orange-red anthers (vs. deep yellow); and a horizontally spreading follicle (vs. spreading follicles).

3.2. Phylogenetic Analysis

Our ITS phylogenetic tree presents a topology similar to those of Huang et al. (2023) [6]. In addition, 10 ITS sequences, most similar to S. yongkangense, (AB088628, AB088626, KM111166, AB088625, KM111164, KM111165, LM993281, MN150061, AB930281, LC229234) were selected (compared by BLAST) (Figure 2). The GTR+I+G was selected for Bayesian analysis. The 50% majority rule consensus tree of all of the post burn-in trees is depicted with Bayesian posterior probabilities (PPs, Figure 2). The Bayesian analysis achieved convergence with an average split-frequency standard deviation of 0.021 and PSRF values averaging 1.005. Key parameters (alpha, pinvar) showed ESS > 3000, ensuring robust posterior sampling. The topology of the ML tree was highly compatible with that of the Bayesian tree, and the BPs are plotted on the Bayesian tree (Figure 2). The phylogenetic analysis shows that the new species S. yongkangense is in a subclade in Acre clade (PP/BS = 0.94/96, Figure 2). The phylogenetic analysis shows that the new species S. yongkangense is sister to a clade in the Acre clade which includes S. bulbiferum and four further Sedum species, well supported by high Bayesian posterior (PP) values and bootstrap (BS) values.

4. Discussion

The morphological analysis reveals that while S. yongkangense, S. ryukyuense, S. mukojimense, S. boninense, and S. bulbiferum share some similar traits, they exhibit distinct characteristics as regards the following characteristics: a biennial life form; sparse, linear, terete, slightly flattened leaf blades; first trifurcating, secondarily bifurcating, showing many flowers in inflorescence; unequal, fleshy, terete, linear sepals; and horizontally spreading follicles. Ecological and phenological comparisons further distinguish S. yongkangense. Unlike its congeners inhabiting volcanic slopes (e.g., S. ryukyuense) or coastal cliffs (S. boninense), S. yongkangense exclusively colonizes limestone crevices at 300–500 m elevations. Its flowering period (April–June) is 2–3 weeks later than the sympatric S. bulbiferum, reducing interspecific competition for pollinators.

While chloroplast markers are commonly used in plant phylogenetics, recent comprehensive studies of Sedum (Messerschmid et al., 2020 [12]) have demonstrated that ITS sequences provide sufficient phylogenetic resolution in the Sedum taxonomy. The nuclear ITS region shows higher evolutionary rates (58.1% parsimony-informative sites) compared to plastid markers (28.2% in concatenated matK/rps16/trnL-F), making it particularly suitable for resolving recently diverged Sedum species. Therefore, our molecular findings unambiguously indicate their separate phylogenetic positions. Together, the morphological and molecular evidence substantiate the conclusion that S. yongkangense is a distinct new species which is grouped in the Acre clade of Crassulaceae and in the sect. Sedum within the genus Sedum.

5. Taxonomic Treatment

Sedum yongkangense Y.L. Xu et Z.H. Chen, sp. nov. (Figure 1, Figure 3 and Figure 4).

Type: CHINA. Zhejiang Province, Yongkang City, Shizhu Town, Xintang Reservoir, on bare rocks, 28°29′35.82″ N, 120°5′7.02″ E, elevation 153 m, 9 May 2024, Y.L. Xu et al., Xu2943 (holotype: ZM barcode ZMNH0067389, Figure 4).

 

Description: Biennial herb, glabrous. Roots fibrous. Sterile stems absent. Fertile stems solitary, erect, branched from near base, ca. 11 cm tall, 1–2 mm in diameter, purplish-red, slender, herbaceous (not succulent). Leaves sparse, alternate; leaf blade terete, slightly flattened, 4–12 × 1–2.8 mm, 1–2 mm thick, apex obtuse, base shortly spurred. Bracts similar to leaves but smaller. Cyme many-flowered, first triple-branched, later double-forked. Flowers sessile. Five sepals, unequal, terete, 4–6.5 × 1.1–1.3 mm, apex obtuse, base shortly spurred, free, obliquely ascending at anthesis, erect in fruit. Five petals, horizontally spreading or slightly reflexed, oblong-lanceolate, yellow, 5–5.5 × 1.5–1.6 mm, apex acute, base gradually narrowed, free. Stamens: 10; antesepalous filaments 4–4.5 mm long; antepetalous filaments 2.5–3 mm long, inserted ca. 1 mm from petal base; anthers orange-red. Nectar scales yellow, obconic, 0.4 × 0.3 mm, apex truncate or retuse. Five carpels, 2.8–3.2 mm long, connate for ca. 1 mm at base; styles ca. 1.2 mm long. Ovules: 8–14, cylindrical, 0.4–0.5 mm long, surface papillate. Follicles horizontally spreading. Seeds: 8–12, ellipsoid, 0.68–0.76 × 0.37–0.43 mm, surface with few papillae near hilum, elsewhere with longitudinally arranged minute pits.

 

Distribution and habitat: The new species is only known from Yongkang City, Zhejiang (Figure 5). It grows on bare rocks at an elevation of about 150–250 m.

 

Phenology: Seedling October; flowering from April to May and fruiting in May to June of the following year.

 

Etymology: The specific epithet ‘yongkangense’ refers to the type locality of the new species.

 

Vernacular name: yǒng kāng jǐng tiān (Chinese pronunciation); 永康景天 (Chinese name).

 

Similar species: The new species is similar to S. ryukyuense Takuro Ito, S. mukojimense Takuro Ito, and S. boninense Yamam. ex Tuyama, but differs in being a biennial herb; its spreading cymes with numerous flowers; unequal, linear, terete sepals; horizontally spreading follicles; and inland habitat.

 

Additional specimens examined (paratypes): on bare rocks in Danxia landform, Machedian Village, Shizhu Town, Yongkang City, Zhejiang Province, cultivated in Hangzhou, 28°50.189′ N, 120°6.942′ E, elevation 256 m, 29 April 2024, Z.H. Chen & W.Y. Xie, Xu2937, on bare rocks in Hengyan Mountain, the 2nd Houtang Village, Gushan Town, Yongkang City, Zhejiang Province, 29°02′97″ N, 120°9′14.12″ E, elevation 206 m, 9 May 2024, J.P. Li, Xu2942, and on bare rocks in Yangxiling, Yangxi Village, Zhoushan Town, Yongkang City, Zhejiang Province, 28°50′4.71″ N, 120°13′16.83″ E, elevation 238 m, 9 May 2024, Y.L. Xu et al., Xu2944.

 

Conservation Status:

Sedum yongkangense is endemic to Yongkang City and Liandu District of Lishui City in Central Zhejiang Province. Current findings indicate a distribution area of approximately 700 km², with six distribution sites, a population habitat area of over 2000 square meters, and an estimated over-20,000 individuals in the wild. Sedum yongkangense qualifies for Vulnerable (VU) status under IUCN Criterion B1ab (iii) due to its restricted geographic range (EOO = 700 km²), limited number of locations (6), and inferred continuing decline in habitat quality from human activities. Urgent conservation measures are needed to address habitat degradation and ensure long-term survival.

 

Key to the species of Sedum (modified from Flora of China, Fu et Ohba, 2001 [5])

1.

Leaf blade flat ........................................................................................................................2

+

Leaf blade terete.....................................................................................................................3

2.

Bulbils in leaf axils; fertile stem congested; sepals unequal; anthers deep

yellow..................................................................................................................S. bulbiferum

+

No bulbils in leaf axils; fertile stem solitary; sepals equal; anthers red.....................

...........................................................................................................................S. mukojimense

3.

Biennial; leaf blade sparse; inflorescences with many flowers; sepals unequal;

follicles horizontal spreading....................................................................S. yongkangense

+

Perennial; leaf blade densely; inflorescences with solitary or 1–12 flowers; sepals

equal; follicles spreading......................................................................................................4

4.

Bulbs form underground after flowering; sterile stem absent; leaf blade 5–16 cm

long; inflorescences with usually 1–3 flowers..................................................S. boninense

+

No bulbs; sterile stem present; leaf blade 3–6 cm long; inflorescences with solitary

flower....................................................................................................................S. ryukyuense