The fossil material was collected from the Ningming Formation at 22°09′15.77′′N, 107°01′23.11′′E (Fig. 1) in the northwestern region of Chengzhong Town, Ningming County, Guangxi, China. The Ningming Formation consists of shallow lacustrine deposits, gray, dark gray mudstone with light yellow shaly siltstone and fine-grained sandstone (Fig. 2; Ning et al., 1994). The age of the Ningming Formation is regarded as Oligocene based on palynostratigraphy (Kuang et al., 2004 and Wang et al., 2003), plant macrofossils (Li et al., 2003), well-preserved fishes (Chen and Chang, 2011, Chen et al., 2004 and Chen et al., 2005) and lithostratigraphy (Li et al., 1995 and Ning et al., 1994).

The experimental treatments for the fossil cuticles were well described in previous studies (Ma et al., 2013 and Wang et al., 2013). Here, we followed these methods with slight modifications. The fossil material was immersed in 10% HCl for one day and then with 50% HF overnight. Cleaned samples were macerated using Schulze's solution, followed by 5% KOH to obtain cuticles. After rinsing with distilled water multiple times, some cuticles were stained with 1% safranine solution for light microscope (LM). Unstained cuticles were mounted on stubs and splutter-coated with gold for scanning electron microscope (SEM).

Extant palms for morphological and cuticular comparisons were collected from trees growing at the South China Botanical Garden, Chinese Academy of Sciences (IBSC). These cuticles were prepared according to the method of Wang et al. (2014). The material was immersed in a 1:1 solution of glacial acetic acid (CH₃COOH) and 30% hydrogen peroxide (H₂O₂) and then placed in a hot water-bath at 80 °C for 10 h. Once the cuticles have turned white and transparent, they can easily be separated. The same procedures for LM preparations were then followed as the method for the fossil cuticles.

All specimens, LM slides, and SEM stubs are deposited at the Institute of Palaeontology and Stratigraphy, Lanzhou University, Gansu Province, China. Morphological descriptions of palm leaves are based on the terminology of EBFC (1991) and Read and Hickey (1972). The terms used by Dilcher (1974) and Wang and Tao (1991) were used for anatomical characters. The abbreviation LDGSW refers to the Institute of Palaeontology and Stratigraphy, Lanzhou University; HNZWY refers to the extant material from IBSC.

Order: ARECALES

Family: ARECACEAE

Subfamily: CORYPHOIDEAE

Fossil species

Three fossil species of Coryphoideae are described as follows. All the voucher specimens were collected from the same locality and stratigraphy, and they are deposited at LDGSW.

Type locality

Chengzhong Town, Ningming County, Guangxi, China (Fig. 1).

Stratigraphy and age

Ningming Formation, Oligocene

Repository

Institute of Palaeontology and Stratigraphy, Lanzhou University, Gansu Province, China.

Genus: Chuniophoenix

Species: Chuniophoenix slenderifolia Q.J. Wang et B.N. Sun sp. nov.

(Fig. 3a–c; Fig. 4a–f; Fig. 9a, b)

Diagnosis: Leaves costapalmate, fan-shaped; costa long and straight; petiole narrow, unarmed. Segments, sparse, emerging asymmetrically from the sides of the costa. Basal segments pendulous. Lamina isobilateral and amphistomatic; with stomatal complexes paratetracytic on the abaxial cuticle and brachyparatetracytic on the adaxial cuticle. Stomatal complexes cyclocytic on the petiole cuticle.

Etymology: The epithet slenderifolia is chosen for the leaf, which looks very slender in general morphology.

Holotype: LDGSW-2013-30-A, B (Fig. 3a and c) (designated here; part and counterpart specimens).

Description: The fossil is fan-shaped (Fig. 3a and c) with a portion of leaf blade and petiole preserved. The petiole exceeds 5.3 cm in length and 1.3 cm in width and is smooth and spineless, tapering upward to form a long straight costa (Fig. 3a and c; Fig. 9a). The costa is at least to 3.8 cm long (Fig. 3a and c). Segments, which emerge asymmetrically from the sides of the costa (Fig. 3a and c; Fig. 9a), are sparse and partially preserved. The basal segments are likely to be pendulous (Fig. 3a; Fig. 9a). Leaf blade divided into approximately 31 segments, which are no less than 7.9 cm long and 0.5–0.7 cm wide (Fig. 3a). Venation is parallel, with some faint, inconspicuous ridges between the ribs of segments (Fig. 3b; Fig. 9b). The ridges may be probable lateral veins and are spaced 0.09–0.18 mm apart. Cross veins are not observed.

In the abaxial cuticle, ordinary epidermal cells (Fig. 4a and e) are regularly arranged in longitudinal files, narrowly rectangular to slender in outline, 5.65–21.54 μm long and 5.08–12.00 μm wide with a length/width (L/W) ratio from 0.5 to 5.6. Epidermal cells surrounding the stomata (Fig. 4d) are shorter and smaller. Stomatal complexes (Fig. 4d) are paratetracytic, 23.42–39.85 μm long and 12.79–26.56 μm wide, with 2 lateral and polar subsidiary cells. Guard cells (Fig. 4d) are irregularly rectangular, 16.07–18.00 μm in length and 2.31–3.77 μm in width, forming a slit-like aperture. Lateral subsidiary cells (Fig. 4d) are kidney-shaped, whereas polar subsidiary cells (Fig. 4d) are widely rectangular. Meanwhile, some stomatal complexes have 3 polar subsidiary cells with 2 at one end of the guard cells.

In the adaxial cuticle, epidermal cells (Fig. 4b) are arranged in longitudinal files more regularly, from rectangular or narrowly rectangular to irregularly polygonal in outline, mostly with rounded corners or perpendicular end walls, 6.45–30.00 μm long and 2.35–23.55 μm wide with a L/W ratio from 0.3 to 7.5. Anticlinal walls are straight, and periclinal walls may be smooth on the inner and outer surfaces (Fig. 4b). Stomatal complexes (Fig. 4b) are brachyparatetracytic, 22.61–33.23 μm long and 10.43–27.42 μm wide, with 2 lateral and polar subsidiary cells. Guard cells (Fig. 4b) are irregularly rectangular, 10.00–19.35 μm in length and 1.74–4.52 μm in width, forming a slit-like aperture. Lateral subsidiary cells (Fig. 4b) are kidney-shaped, whereas polar subsidiary cells (Fig. 4b) are wide rectangular. However, some stomatal complexes have irregular shapes, and their polar subsidiary cells are irregularly polygonal. Trichomes are not observed.

Epidermal cells of the petiole cuticle (Fig. 4c and f) are regularly arranged in longitudinal files, triangular, nearly square, rectangular or irregularly polygonal in outline, mostly with perpendicular end walls, 3.48–18.59 μm long and 5.13–10.14 μm wide with a L/W ratio from 0.4 to 2.6. Anticlinal walls of the epidermal cells are straight, and periclinal walls may be smooth on the inner and outer surfaces (Fig. 4c and f). Stomatal complexes (Fig. 4c and f) are typically cyclocytic, ranging from 20.51–35.90 μm in diameter. They typically possess 6 lateral subsidiary cells, which are elongate (Fig. 4c and f). Trichomes are not observed.

Large damaged areas are commonly found on the leaf blade and petiole cuticles (Fig. 4c and e), consisting of many thin-walled cells. These cells are irregularly arranged, polygonal or isodiametric, 5.13–13.29 μm long and 5.70–10.90 μm wide, with a L/W ratio from 0.5 to 2.3. The damaged areas are similar to those observed on extant palms (Fig. 8h).

Comparison: Our material is assigned to the living genus Chuniophoenix based on the following similarities (Fig. 3a, c and d; Fig. 9a): asymmetrical leaf base, segments sparsely emerging from the sides of the costa, long straight costa with indistinct margins. Additionally, the cuticular characteristics of the leaf blade and petiole are also similar to those of extant C. hainanensis Burret, such as the paratetracytic stomatal complexes (Fig. 4a, d and g) and the shapes of epidermal cells (Fig. 4c, f and i). The most notable characteristic is the basal segments that emerge asymmetrically from the sides of the costa (Fig. 3a and c; Fig. 9a), which is very similar to that of C. hainanensis (Fig. 3d). However, C. humilis Burret, which is considered to be costapalmate with a very small costa by some authorities (Henderson, 2009) or palmate by others (Dransfield et al., 2008), differs from the fossil in the distinctly narrow petiole (Fig. 10a) and cuticular characteristics (Fig. 10d and g). Asymmetrical leaf bases are also represented in other living Arecaceae (EBFC, 1991 and Zhou et al., 2013), such as members of the genera Bismarckia, Hyphaene, Latania and Sabal. However, Bismarckia, which is a monotypic genus endemic to Madagascar, has a robust petiole (about 3.5–5.5 cm) and approximately 75 folded segments (Brown, 2013; http://www.palmweb.org/node/2). The petioles of extant Hyphaene are 2–6 cm wide and armed with robust, triangular spines (about 1–3.5 cm long and 1.5 cm wide) (http://www.palmweb.org/node/2). Latania is native to islands in the western Indian Ocean, whose leaves differ in possessing robust petioles (≥ 2 cm) and broader segments (about 2.3–3.3 cm in width). Although asymmetrical leaf bases are common in extant Sabal, such as S. bermudana L.H. Bailey, S. mexicana Mart. and S. minor (Jacq.) Pers. (Fig. 10c), these species differ in possessing a wide and robust petiole (about 2.2–3.3 cm) (the measurement data from the Herbarium Catalogue, Royal Botanic Garden, Kew). Moreover, their segments are much wider than that in the fossil and differ for their cuticular characteristics (Fig. 10e, f, h and i).

The asymmetrical leaf base is uncommon among fossil palm leaves. Only two Sabalites species, S. asymmetricus Jin et Zhou and Sabalites sp. from the Eocene of Hainan, China, are more or less similar to the new species in gross morphology. The former has more segments (26 pairs) and a wide petiole (Zhou et al., 2013). The basal segments of Sabalites sp. (Guo, 1965) are perpendicular to the petiole and differ from the pendulous basal segments of the new species (Fig. 5, a, d, e). Additionally, the costa of Sabalites sp. is more distinct (Guo, 1965) than that of our specimens. Despite some similar morphologies found on other reported fossil and modern palms, there are some distinct differences observed between them and the new species (Appendix A). Therefore, the present palm fossil cannot be definitively assigned to a reported fossil or extant species and thus is described as a new species, C. slenderifolia sp. nov.

Genus: Livistona

Species: Livistona roundifolia Q.J. Wang et B.N. Sun sp. nov.

(Fig. 5a, b, d, e and g–i; Fig. 6a–g; Fig. 9c)

Diagnosis: Leaves costapalmate, fan-shaped; costa stout; petiole wide, armed with robust spines. The petiole spines varing in size and curved. Some of the spines forming extended, arcuate connections with adjacent spines. Segments, emerging symmetrically from the petiole apex and the bilateral sides of the costa. Basal segments emerge from the petiole apex at an obtuse angle, making the shape of the leaf base rounded. Lamina bifacial and hypostomatic; stomatal complexes brachyparatetracytic on the leaf cuticle and paratetracytic on the petiole cuticle.

Etymology: The epithet roundifolia is chosen for the basal segments, which emerge approximately from the petiole apex at an obtuse angle and make the shape of the leaf base rounded.

Holotype: LDGSW-2013-66-A, B (Fig. 5a and b) (designated here; part and counterpart specimens).

Paratypes: LDGSW-2013-07, LDGSW-2013-67, LDGSW-2013-68, LDGSW-2013-89 (Fig. 5h, d, g and e) (designated here)

Description: The holotype (Fig. 5a and b) preserves the basal portion of a fan-shaped leaf blade and the top of petiole. The petiole exceeds 11.6 cm in length (Fig. 5e) and 2.7 cm in width (Fig. 5a and e) and is smooth, tapering upward to form a stout costa (Fig. 5a and b; Fig. 9c). The petiole spines vary significantly in size (Fig. 5a, d and e) and are 3.19–5.69 mm in length, with large spines alternating with one or two small ones (Fig. 5e; Fig. 9c). The spines are spaced 2.84–3.29 mm apart along the petiole and are curved (Fig. 5d and e). The bases of the spines are 2.59–4.17 mm in width of the small ones, and 4.91–7.41 mm in width of the large ones. Some of the spines form extended, arcuate connections with adjacent spines (Fig. 5e). The costa (Fig. 5a and b; Fig. 9c) is at least to 3.2 cm long. Segments, which are partially preserved, emerge symmetrically from the petiole apex (Fig. 5a) and along the sides of the costa (Fig. 5a and b). The basal segments arise from the petiole apex at an obtuse angle, and the shape of the leaf base is nearly rounded (Fig. 5a and b; Fig. 9c). Segments, approximarely 32 pairs (Fig. 5a and b), are no less than 4.5 cm long (Fig. 5a). Venation is parallel and lateral veins are faint, spaced 0.45–0.51 mm apart (Fig. 5i). Cross veins are not observed.

Leaves are hypostomatic. The stomatal complexes (Fig. 6a, d and g) are typically brachyparatetracytic, 24.71–33.53 μm long and 18.24–27.33 μm wide, with 2 lateral and polar subsidiary cells. Guard cells (Fig. 6a and d) are crescent-shaped, 14.71–17.06 μm in length and 1.76–2.94 μm in width, forming a slightly wide aperture (Fig. 6a, d and g). Lateral subsidiary cells (Fig. 6a and d) are irregularly rectangular, whereas polar subsidiary cells (Fig. 6a and d) are wide rectangular.

In the abaxial cuticle, ordinary epidermal cells (Fig. 6a and d) are more or less regularly arranged in longitudinal files, from sub-square or rectangular to irregularly polygonal in outline, mostly with oblique end walls, 6.83–16.50 μm long and 5.29–13.00 μm wide with a L/W ratio from 0.8 to 2.4. Epidermal cells of the adaxial cuticle (Fig. 6b and e) are more regularly arranged in longitudinal files, sub-square, rectangular, triangular, isodiametric, or irregularly polygonal in outline, mostly with sharp corners or oblique end walls, 5.06–16.29 μm long and 6.18–11.24 μm wide with a L/W ratio from 0.5 to 1.8. Anticlinal walls are straight and strongly cutinized, forming prominent flanges on the inner surface (Fig. 6e), whereas periclinal walls are smooth on the inner and outer surfaces (Fig. 6b and e). Trichomes are not observed.

Cuticles of the petiole are thicker. Epidermal cells (Fig. 6c) are similar to those of the adaxial cuticle in morphology but are more rectangular to elongate or slightly elongate, arranged in regularly longitudinal files, 3.08–12.12 μm long and 2.15–8.18 μm wide with a L/W ratio from 0.9 to 2.7. Anticlinal walls (Fig. 6c) are straight, whereas periclinal walls may be smooth on the inner and outer surfaces. Stomatal complexes (Fig. 6c and f) are paratetracytic, 14.15–30.30 μm long and 10.46–19.55 μm wide, with 2 lateral and polar subsidiary cells. Guard cells (Fig. 6c and f) are elongate, 10.46–20.12 μm in length and 1.82–3.05 μm in width, forming a slightly wide aperture (Fig. 6f). Lateral subsidiary cells (Fig. 6c and f) are crescent-shaped, but polar subsidiary cells (Fig. 6c and f) are inconspicuous, with ill-marked ridges. Trichomes are not observed.

Similarly large damaged areas are also found on the petiole cuticle (Fig. 6c). These thin-walled cells are 3.69–5.23 μm long and 3.07–3.08 μm wide, with a L/W ratio from 1.2 to 1.7.

Comparison: The present fossil is attributed to the genus Livistona primarily based on the following characteristics of the spines (Fig. 5a, d and e; Fig. 9c): •

they vary significantly in size with large ones alternating with small ones;

All these characteristics are well corresponded to the petiole spines of extant L. chinensis (Jacq.) R. Br. ex Mart. (Fig. 5f). In addition, the fossil shows some similarities to extant Livistona in the anatomical characters of the leaf blade and petiole. Firstly, the anticlinal walls of the epidermal cells are strongly cutinized for the fossil and extant L. saribus (Lour.) Merr. ex A. Chev. (Fig. 6k). Second, the stomatal complexes of the petioles all are paratetracytic between the present material and L. saribus (Fig. 6f and l). According to Read and Rickey (1972), the petioles of Sabalites and Palmacites are unarmed, and thus, the taxon does not belong to these fossil genera. Although armed petioles are common in extant Borassus, Hyphaene, Satranala, Trachycarpus and Licuala, there are some evident differences between them and the present fossil. The petiole teeth of Borassus can be divided into two types: large (0.3–2.8 cm long) and small serrate (0.1–0.85 cm long). The two types of teeth usually are heavily armed on the petiole margins (Dransfield et al., 2008; http://www.palmweb.org/node/2). The petiole spines of extant Hyphaene, which are generally uniform in size (1–3.5 cm long and 1.5 cm wide) and shape (triangular), distinctly differ from the spines of the present species. Satranala, which is endemic to Madagascar, has armed petioles with minutely irregular teeth (Dransfield et al., 2008; http://www.palmweb.org/node/2). Extant Trachycarpus species are armed with very fine teeth on the petioles (Dransfield et al., 2008 and EBFC, 1991; http://www.palmweb.org/node/2). The teeth of Satranala and Trachycarpus are not curved and noticeably acute, but minutely rounded or verrucate. The petioles of Licuala are no more than 1.5 cm in width (personal observation), which are narrower than those of our fossil.

The presence of spines on the petiole margins is uncommon among palm fossils. A few Hyphaene fossils with spiny petioles preserved are reported from the Oligocene of Ethiopia (Pan et al., 2006): H. kappelmanii A.D. Pan, B.F. Jacobs, J. Dransf. & W.J. Baker and Hyphaene sp. However, H. kappelmanii is characterized by the presence of noticeably curved spines on the narrow petiole. Petioles referred to Hyphaene sp. differ in possessing sharp spines. L. tibetica Tao from the Eocene of Xizang (Tao, 1988; Appendix B) and Livistona sp. from the Eocene of Hainan (Zhou et al., 2013), which lack detailed cuticular and morphological analysis, respectively, cannot be readily compared with the fossil.

Based on comparisons with other fossils and modern palms (Appendix A), a new specific name is proposed for the present fossil palm, L. roundifolia sp. nov.

Genus: Trachycarpus

Species: Trachycarpus formosa Q.J. Wang et B.N. Sun sp. nov.

(Fig. 7a–e; Fig. 8a–g; Fig. 9d, e)

Diagnosis: Leaves costapalmate, fan-shaped; costa robust, triangular; petiole wide. Segments, emerging symmetrically from the petiole apex and the bilateral sides of the costa. Leaf base cordate. Lamina bifacial and hypostomatic; stomatal complexes paratetracytic on the leaf cuticle and brachyparacytic on the petiole cuticle.

Etymology: The epithet formosa is chosen for the basal segments, which make the leaf blade beautiful and finely formed.

Holotype: LDGSW-2013-03-A, B (Fig. 7a and b) (designated here; part and counterpart specimens).

Paratypes: LDGSW-2013-77-A, B (Fig. 7c and d) (designated here; part and counterpart specimens).

Description: The fossil is fan-shaped (Fig. 7a and b) with the basal portion of leaf blade and the top of petiole preserved. The petiole (Fig. 7a) exceeds 5.1 cm long and 3.1 cm wide, smooth, tapering upward to form a robust costa (Fig. 7a and b; Fig. 9d). The costa is nearly triangular and 3.5 cm long (Fig. 7a and b). Segments, which are partially preserved, emerge symmetrically from the petiole apex (Fig. 7a and b) and along the sides of the costa (Fig. 7a–d). The basal segments (Fig. 7a and b; Fig. 9d) first curve obviously downward and then strongly upward, and the leaf base is cordate. Segments, approximately 40 pairs (Fig. 7a), are no less than 8.6 cm long and 1.3 cm wide. Venation is parallel (Fig. 7e), with lateral veins faint (Fig. 7e; Fig. 9e) and spaced 0.65–1.02 mm apart. Cross veins (Fig. 7e; Fig. 9e) connect two adjacent parallel veins and most are oblique to them, spaced 1.16–2.96 mm apart.

The leaves are hypostomatic, and stomatal complexes (Fig. 8a, d and g) are paratetracytic, 30.86–43.68 μm long and 19.19–32.50 μm wide, with 2 lateral and polar subsidiary cells. Guard cells (Fig. 8d and g) are elongate, 18.55–22.22 μm in length and 3.87–8.02 μm in width, forming a slit-like aperture. Lateral subsidiary cells (Fig. 8d) are reniform, whereas polar subsidiary cells are wide rectangular.

Ordinary epidermal cells of the abaxial cuticle (Fig. 8a) are more or less regularly arranged in longitudinal files, rectangular to irregularly polygonal in outline, mostly with perpendicular end walls, 7.41–20.37 μm long and 4.32–11.11 μm wide with a L/W ratio from 0.7 to 4.1. The epidermal cells surrounding the stomata (Fig. 8d and g) are shorter and smaller than ordinary ones. Epidermal cells of the adaxial cuticle (Fig. 8b and e) are similar to those of the abaxial cuticle in morphology but are more regularly arranged in longitudinal files (Fig. 8h), 7.54–24.05 μm long and 5.06–10.13 μm wide with a L/W ratio from 0.9 to 3.5. Anticlinal walls of the epidermal cells on both cuticles are straight, with some strongly cutinized, and they form prominent flanges on the inner surface (Fig. 8e and g). Periclinal walls are smooth on the inner and outer surfaces (Fig. 8a, b, d, e, g). No trichomes are observed.

In the petiole cuticle, epidermal cells (Fig. 8c) are more regularly arranged in longitudinal files, rectangular, irregularly polygonal in outline, mostly with rounded corners or oblique end walls, 9.76–32.93 μm long and 4.88–8.13 μm wide with a L/W ratio from 1.3 to 4.5. Anticlinal walls are straight, whereas periclinal walls may be smooth on the inner and outer surfaces (Fig. 8c). Stomatal complexes (Fig. 8c and f) are brachyparacytic, 30.00–48.13 μm long and 23.13–36.25 μm wide. They bear only 2 lateral subsidiary cells, with polar subsidiary cells absent or inconspicuous (Fig. 8f). Guard cells (Fig. 8c and f) are elongate, 18.13–21.95 μm in length and 1.88–4.27 μm in width, forming a slit-like aperture. Subsidiary cells (Fig. 8f) are fusiform. Trichomes were not observed.

Large damaged areas are also found on the leaf blade and petiole cuticles (Fig. 8b and c). These thin-walled cells are 7.14–19.48 μm long and 4.38–11.69 μm wide, with a L/W ratio from 1.0 to 3.1.

Comparison: The present fossil is placed in the living genus Trachycarpus primarily based on the triangular costa and the anatomical characters. Moreover, the fossil and T. fortunei have similar venation patterns (Fig. 7e and g; Fig. 9e). The triangular costa can be appropriately compared with that of T. fortunei (Hooker) H. Wendland (Fig. 7a and f). Although similarly triangular costa can be also found between other fossil and extant palms, there are differences between these palms and the present material. S. campbelli (Newberry) Lesquereux, from the Paleo-Eocene of America (Lesquereux, 1878 and Newberry, 1898), differs from the present material in possessing truncate leaf base (EBCPC, 1978 and Guo, 1965). S. szei Guo, from the Eocene of China (Guo, 1965 and Zhou et al., 2013), is different in the following aspects: the segments are no more than 5 mm in width; and the petiole are ridged. Besides, the cordate leaf base (Fig. 7a and b) rarely occurs in the fossil record. Although some palm fossils might have a similar leaf bases, such as S. inquirenda Knowlton and S. grayanus Lesquereux. S. inquirenda, from the Paleocene of America (Knowlton, 1917), differs in having more narrower segments (< 5 mm). S. grayanus, which is known from Late Cretaceous to Eocene and described from many localities of North America (Knowlton, 1930 and Lesquereux, 1878), can be distinguished by its broader segments (about 5 cm). S. changchangensis Guo, from the Eocene of Hainan, China (Guo, 1965 and Zhou et al., 2013), is also characterized by the cordate leaf base, but it differs in possessing a long straight costa (about 0.5 cm wide and 6 cm long) and a narrow petiole (1.5 cm in width).

The triangular costa is also represented in other extant palms, such as L. chinensis, S. gretherae H.J. Quero, T. martianus (Wall.) H. Wendland and some members of Borassus. The petioles of L. chinensis are characterized by the presence of robust spines (Fig. 5f). S. gretherae has more segments (50–60 pairs) and broader petioles (5–6 cm wide in the middle and 3–4 cm wide at the apex). The triangular costa of T. martianus is no more than 1 cm long (EBFC, 1991) and clearly differs from that of T. formosa sp. nov. Armed petioles are characteristic of Borassus, whose petioles all are heavily armed by teeth apart from Borassus heineanus Becc. (Dransfield et al., 2008; http://www.palmweb.org/node/2).

Anatomically, the new species and T. martianus all are characterized by hypostomatic leaves only with stomata on the abaxial cuticle (Fig. 8a and j), although T. fortunei is amphistomatic with rare stomata on the adaxial cuticle. Stomatal complexes of T. formosa sp. nov. are paratetracytic (Fig. 8a, d and g), similar in general morphology to those of the living species T. fortunei and T. martianus (Fig. 8h and j), although with some variations in the shapes of their subsidiary cells. Moreover, the stomatal distribution of the fossil and T. fortunei has a similar density on the abaxial cuticle (Fig. 8a and j). In particular, the petiole cuticles of the new species and T. fortunei all consist of densely epidermal cells (Fig. 8c and f), which are rectangular or irregularly polygonal with rounded corners or oblique end walls. Thus, the fossil from Ningming is confirmed to have a close affinity to the living Trachycarpus based on the similarities of the morphological and cuticular characteristics. Although the petioles of the extant Trachycarpus are armed with minutely rounded or verrucate spines, the petiole spines are inconspicuous (Fig. 7f; Dransfield et al., 2008 and EBFC, 1991). However, some extant palms share more or less similarities with the fossil in the cuticular characteristics (Appendix A), such as Chuniophoenix and Sabal. C. hainanensis Burret, which are also characterized by hypostomatic leaves, can be easily excluded from the fossil because of the attachment mode of basal segments (Fig. 3d). S. rosei (O.F. Cook) Becc., which is endemic to the coast of northwestern Mexico, has a long straight costa (Fig. 10b) and thus differs from the fossil. S. minor (Jacq.) Pers., which is native to the southeastern United States and characterized by a slightly asymmetrical leaf base, differs from the fossil in possessing a long narrow costa (Fig. 10c). Other Sabal, such as S. bermudana L.H. Bailey and S. mexicana Mart., can easily be distinguished from the fossil by their stomatal patterns (Fig. 10h and i).

Based on the morphological and cuticular comparisons with fossil and modern palms (Appendix A), we describe the present specimens as a new species, T. formosa sp. nov.

Palms are characteristic components of tropical rain forests; thus, understanding the phylogeny and distribution of Chinese palms in time and space is fundamental in tracking the evolution of tropical rain forests in China. Although the palm flora in China has about 76 species in 17 genera, their fossils are relatively rare reported (Fig. 11; Appendix B). To date, there are 7 localities around China that have yielded palm fossils, with 15 species reported. The earliest fossils are represented by unarmed isolated segments. Amesoneuron sp., the earliest leaf, is described from the Early Cretaceous of Pingzhou, Hokong (the age of the Pingzhou flora is regarded as Albian based on plant macrofossils; Zhou et al., 1990), suggesting that palms have been established in China since the Early Cretaceous. Geographically, the occurrence of palm fossils from Xizang (Tao, 1988; Appendix B) indicates that the genus Livistona had reached the floras of western China by at least the Eocene. Palm remains are relatively abundant in the Eocene Changchang Formation of Hainan (Zhou et al., 2013), with 7 morphospecies of fossil genera and 1 undefined species of the living genus Livistona. The high diversity may be an indication that palms were prevalent components of the Changchang flora. Other leaf fossils are also reported from the Eocene of Liaoning (Endo, 1934) and Guangxi (Guo, 1965). To date, this fossil record from Liaoning is at higher latitude than any other previous fossil records in China. So, the fossils from Liaoning, Guangxi, Xizang and Hainan show that palms in China had a wide distribution during the Eocene (Fig. 11; Appendix B). The narrow distribution of Chinese palms today (Fig. 11) may be linked to the deteriorating climates since the Eocene, such as more seasonal, arid and cooling climates (Baker and Couvreur, 2013b, Harley and Morley, 1995, Kissling et al., 2012 and Pan et al., 2006). The present discovery in Guangxi represents the only palm fossils from the Oligocene of China and provides new fossil evidence about the palm biogeography in this country. The presence of Chuniophoenix fossil is significant because it is the first fossil record of the taxon. Chuniophoenix is endemic to southern China and northern Vietnam (Dransfield et al., 2008 and EBFC, 1991). This report indicates that Chuniophoenix has occurred in China over a long geological period. In China, Livistona has been reported dating back to the Eocene, with two species recorded (Tao, 1988 and Zhou et al., 2013; Appendix B). The occurrence of a Livistona fossil from Guangxi offers new data about the Livistona diversity in the Eocene of China, which indicates that Chinese Livistona has at least two species at that time. Extant Trachycarpus palms are native to Asia, from the eastern Himalayas to eastern China. So far, no Trachycarpus fossil is reported from this country. The Trachycarpus fossil is the first record from its modern area of distribution and demonstrates that there was Trachycarpus growing in China since the Oligocene. In the Neogene, Chinese palm fossils were extremely rare, with only one leaf species from the Miocene of Guangdong (Guo, 1965). The lower frequency of palm fossils in the Neogene–Quaternary of this country may be a result of taphonomic biases or/and few paleobotanical studies. Better understanding of the palm biogeography in China requires further work that incorporates molecular analysis and new fossil records.

The origin and evolution of species-rich biomes raise fundamental questions regarding the diversification of palms (Bjorholm et al., 2006, Ling, 2002 and Wei, 1995). The Arecaceae is widespread yet shows high rates of endemism at varied spatial scales (Eiserhardt et al., 2011). The diversity of extant palms in Guangxi is one of the highest in China, both at the community and species levels (EBFC, 1991 and Wei, 1997). Most of the palm vegetation types are found in Guangxi (EBFC, 1991 and Wei, 1997), ranging from tropical to subtropical, temperate (e.g., Chamaerops), alpine (e.g., Trachycarpus) and xerophyte (e. g., Phoenix). Three subfamilies, namely, Coryphoideae, Calamoideae and Arecoideae, in 12 genera and 40 species, occur in Guangxi (EBFC, 1991 and Wei, 1997). Only one species of Trachycarpus and two species of Livistona with costapalmate leaves are among the extant Guangxi flora (EBFC, 1991 and Wei, 1997). However, all the palm fossils from Ningming are fan-shaped with no pinnate leaves recorded. It is in contrast to the extant palm flora of Guangxi, which is dominated by pinnate-leaved palms (EBFC, 1991 and Wei, 1997). So, the occurrence of C. slenderifolia sp. nov., L. roundifolia sp. nov. and T. formosa sp. nov., may suggest that costapalmate palms in the palm flora of Ningming had relatively high diversity during the Oligocene.

The presence of coryphoid palms provides growing evidence that the Ningming flora had a greater diversity during the Oligocene. Preliminary floristic study indicates that the Ningming flora represents a subtropical evergreen forest with some tropical elements. Angiosperms are absolutely dominant in this flora, including Fabaceae, Lauraceae, Fagaceae, Moraceae, Arecaceae, Hamamelidaceae, Betulaceae, Anacardiaceae, Simaroubaceae, Juglandaceae, Ulmaceae and Sapindaceae (Shi et al., 2012). So, the high species richness of costapalmate palms also supports the above-mentioned interpretation.

Palm fossils collected from the Oligocene deposits are assigned to three living genera and three new species, namely, C. slenderifolia sp. nov., L. roundifolia sp. nov. and T. formosa sp. nov. Our findings indicate that palms occurred in Guangxi over a longer geological period and suggest that a diversified palm flora was already present during the Oligocene in Guangxi. Additionally, the report provides a general survey of the occurrence of palm fossils in China, which provides important data on the biogeographical history of Chinese palms and is beneficial to tracking the evolution of Chinese rainforests over geological time.