Research Article |
Corresponding author: Kun Sun ( nwnubotany@163.com ) Academic editor: Patrick Herendeen
© 2022 Xiang Zhao, Qinzheng Hou, Meina Du, Hui Zhang, Lingyun Jia, Zhihua Zhang, Zongqi Ma, Kun Sun.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Zhao X, Hou Q, Du M, Zhang H, Jia L, Zhang Z, Ma Z, Sun K (2022) Micromorphological leaf epidermal traits as potential taxonomic markers for infrageneric classification of Oxytropis (Fabaceae). PhytoKeys 201: 51-76. https://doi.org/10.3897/phytokeys.201.85154
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The characteristics of the leaf epidermis have proven to be useful criteria to support taxonomic studies within Fabaceae. However, there are few systematic studies on the taxonomic significance of leaf epidermis of Oxytropis DC. Here, we used light and scanning electron microscopy to investigate leaf epidermal characteristics of 18 species of genus Oxytropis from the Northeastern Margin of Qinghai-Tibet Plateau. Our examination showed two main types of leaf epidermal cells: polygonal and irregular, and four different patterns of anticlinal walls: straight-arched, sinuolate, undulate, and sinuate. All species studied possess anomocytic stomata. Two trichome shapes were identified: strip-like trichomes, that were present only in O. ciliata, and cylindrical trichomes, present in all other species. Epidermal cell shape and anticlinal wall pattern were constant within species and are useful for species delimitation within genus Oxytropis, when combined with other macroscopic traits. The shape of trichomes can be useful for distinguishing O. ciliata from the other investigated species. Stomatal type was the same within the genus and may be used to elaborate the phylogenetic relationships between genera in combination with data on stomata from other genera. Cluster analysis results were largely consistent with the classification of species and sections based on macro morphological data, indicating that foliar epidermis characteristics of Oxytropis can be used as markers for taxonomic identification at the infrageneric classification level. Lastly, our results support the delineation of the section Leucopodia as an independent section but do not support the merging of section Gobicola into section Baicalia.
China, cluster analysis, leaf epidermis, LM, Oxytropis, SEM, taxonomy
Genus Oxytropis DC. is one of the largest groups within Fabaceae, with approximately 330 species occurring in the cold mountainous regions of Europe, Asia, and North America, and also concentrated in Central Asia (
Leaf epidermal anatomical features, such as epidermal cell shape, epicuticular waxes (
Leaf epidermal features are also valuable for classification at the species level in Fabaceae. For example,
Previous studies have investigated different aspects of Oxytropis, including cytology (
All leaf samples were obtained from specimens deposited at the herbarium of the Northwest Normal University. The materials investigated are listed in Table
Section | Code | Species | Locality | Coordinates | Habitat | Voucher |
---|---|---|---|---|---|---|
Section Xerobia | 1 | O. ciliata | Yueliang Mountain | 36°25'41.85"N, 105°42'23.71"E | Valley | X. Zhao 1947 |
Section Polyadena | 2 | O. muricata | Maxian Mountain | 35°47'46.48"N, 103°58'12.64"E | Sunny hillside | X. Zhao 1903 |
Section Falcicarpae | 3 | O. falcata | Awangcang wetland park | 33°45'32.85"N, 101°41'6.58"E | Riverside | X. Zhao 1842 |
Section Baicalia | 4 | O. ochrantha | Dangzhou grassland | 34°56'54.09"N, 102°53'8.74"E | Alpine meadow | X. Zhao 1813 |
5 | O. bicolor | Tiemu Mountain | 35°58'32.21"N, 104°46'31.40"E | Sunny hillside | X. Zhao 1927 | |
6 | O. racemosa | Yanchi | 37°43'52.02"N, 107°23'55.77"E | Desert sandy land | X. Zhao 1946 | |
7 | O. myriophylla | Maxian Mountain | 35°47'46.48"N, 103°58'12.64"E | Valley | X. Zhao 1833 | |
Section Lycotriche | 8 | O. aciphylla | Jijiquan nature reserve | 38°59'43"N, 101°55'39"E | Desert sandy land | X. Zhao 1924 |
Section Eumorpha | 9 | O. imbricata | Taohe river | 34°33'28.66"N, 102°34'53.99"E | Riverside | X. Zhao 1940 |
10 | O. coerulea | Taitong Mountain | 35°30'8.94"N, 106°35'54.90"E | Border of Forest | X. Zhao 1832 | |
Section Mesogaea | 11 | O. xinglongshanica | Xinglong Mountain | 35°46'20.53"N, 104°1'2.49"E | Valley | X. Zhao 1913 |
12 | O. glabra | Rabah Lake National Nature Reserve | 37°42'3.19"N, 107°2'33.46"E | Desert sandy land | X. Zhao 1950 | |
13 | O. kansuensis | Azi Test Station of LZU | 33°39'57.96"N, 101°52'22.44"E | Alpine meadow | X. Zhao 1819 | |
14 | O. melanocalyx | Guanggai Mountain | 34°24'23.35"N, 102°53'58.80"E | Alpine meadow | X. Zhao 1956 | |
15 | O. taochensis | Liupan Mountain | 35°33'21.81"N, 106°25'21.54"E | Border of Forest | X. Zhao 1838 | |
16 | O. ochrocephala | Xinglong Mountain | 35°47'5.17"N, 104°0'0.67"E | Beside farmland | X. Zhao 1828 | |
17 | O. ochrocephala | Dangzhou grassland | 34°56'54.11"N, 102°53'8.81"E | Alpine meadow | X. Zhao 1812 | |
Section Oxytropis | 18 | O. latibracteata | Helan Mountain | 38°39'46.59"E 105°49'20.25"N | Border of Forest | X. Zhao 1951 |
Section Leucopodia | 19 | O. squammulosa | Shaochagou | 35°42'57.20"N, 105°2'21.20"E | Arid steppe | X. Zhao 1928 |
Leaf epidermal terminology was based on the classification proposed by
SI = S/E + S (1)
where, SI is the stomatal index, S is the number of stomata per unit area, and E is the number of epidermal cells per unit area. Stomatal density (SD) was expressed as the number of stomata per unit leaf area.
Statistical data was processed by the Origin 2021 software (
Species | Adaxial epidermis | Abaxial epidermis | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Shape of trichromes | Ornamentation of trichromes | Inner margin of outer stomatal rim | Ornamentation of outer stomatal rim | Waxy layer of epidermal cells | Shape of cells | Pattern of anticlinal walls | Shape of trichromes | Ornamentation of trichromes | Inner margin of outer stomatal rim | Ornamentation of outer stomatal rim | Waxy layer of epidermal cells | Shape of cells | Pattern of anticlinal walls | |
O. ciliata | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 2 | 2 | 1 | 1 | 1 | 1 | 2 |
O. muricata | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 0 | 0 | 0 | 0 | 1 |
O. falcata | 1 | 1 | 0 | 0 | 2 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 1 |
O. ochrantha | 1 | 0 | 0 | 1 | 0 | 0 | 0 | 1 | 0 | 1 | 1 | 1 | 0 | 3 |
O. bicolor | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 0 | 3 |
O. racemosa | 1 | 1 | 0 | 0 | 2 | 1 | 2 | 1 | 1 | 0 | 0 | 0 | 0 | 3 |
O. myriophylla | 1 | 0 | 0 | 0 | 1 | 1 | 2 | 1 | 0 | 0 | 0 | 2 | 1 | 2 |
O. aciphylla | 1 | 1 | 0 | 2 | 2 | 1 | 2 | 1 | 1 | 0 | 0 | 0 | 1 | 2 |
O. imbricata | 1 | 1 | 0 | 0 | 0 | 1 | 2 | 1 | 1 | 0 | 1 | 1 | 1 | 2 |
O. coerulea | 1 | 1 | 0 | 3 | 0 | 0 | 0 | 2 | 0 | 0 | 3 | 0 | 0 | 1 |
O. xinglongshanica | 1 | 1 | 0 | 2 | 2 | 1 | 2 | 1 | 1 | 0 | 2 | 2 | 1 | 2 |
O. glabra | 1 | 1 | 1 | 0 | 1 | 1 | 2 | 1 | 1 | 0 | 0 | 0 | 0 | 3 |
O. kansuensis | 1 | 1 | 0 | 0 | 0 | 1 | 2 | 1 | 1 | 0 | 0 | 0 | 0 | 3 |
O. melanocalyx | 1 | 1 | 0 | 2 | 2 | 1 | 2 | 1 | 1 | 0 | 1 | 1 | 0 | 3 |
O. taochensis | 1 | 1 | 0 | 2 | 2 | 1 | 2 | 1 | 1 | 0 | 0 | 0 | 0 | 3 |
O. ochrocephala (XLS) | 1 | 1 | 0 | 2 | 2 | 1 | 2 | 1 | 1 | 0 | 1 | 1 | 0 | 1 |
O. ochrocephala (HZ) | 1 | 1 | 0 | 2 | 2 | 1 | 2 | 1 | 1 | 0 | 1 | 1 | 0 | 1 |
O. latibracteata | 1 | 1 | 1 | 1 | 1 | 0 | 3 | 1 | 1 | 0 | 1 | 1 | 0 | 1 |
O. squammulosa | 2 | 2 | 0 | 0 | 0 | 0 | 3 | 2 | 2 | 0 | 0 | 0 | 0 | 1 |
Epidermal cell traits varied within a wide range. The shape varied from polygonal to irregular with straight arched, sinuolate, undulate, and sinuate wall patterns (Table
Characteristics of the leaf epidermis of Oxytropis under light microscopy (surface view).
Species | Adaxial epidermis | Abaxial epidermis | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Shape of cells | Pattern of anticlinal walls | Type of stomata | Mean stomatal density /(mm2) | Mean stomatal index /% | Mean stomatal size /mm2 | Shape of cells | Pattern of anticlinal walls | Type of stomata | Mean stomatal density /(mm2) | Mean stomatal index /% | Mean stomatal size /mm2 | Adaxial and abaxial SD ratio | Adaxial and abaxial SI ratio | |
O. ciliata | Irregular | Sinuolate | Anomocytic | 131.77 | 0.21 | 639.84 (27.88×22.95) | Polygonal | Straight arched | Anomocytic | 63.54 | 0.11 | 748.35 (30.2×24.78) | 2.07 | 1.90 |
O. muricata | Irregular | Sinuolate | Anomocytic | 129.92 | 0.17 | 647.79 (29.01×22.33) | Irregular | Sinuate | Anomocytic | 66.14 | 0.11 | 810.79 (31.61×25.65) | 1.96 | 1.54 |
O. falcata | Irregular | Sinuate | Anomocytic | 170.87 | 0.17 | 571.99 (26.42×21.65) | Irregular | Sinuate | Anomocytic | 81.99 | 0.1 | 669.96 (28.94×23.15) | 2.08 | 1.7 |
O. ochrantha | Irregular | Sinuolate | Anomocytic | 156.4 | 0.19 | 511.08 (24.69×20.7) | Irregular | Undulate | Anomocytic | 95.08 | 0.1 | 541.54 (25.69×21.08) | 1.64 | 1.9 |
O. bicolor | Irregular | Sinuolate | Anomocytic | 110.24 | 0.23 | 448.58 (24.58×18.25) | Irregular | Undulate | Anomocytic | 77.17 | 0.16 | 497.51 (23.59×21.09) | 1.42 | 1.43 |
O. racemosa | Polygonal | Straight arched | Anomocytic | 292.82 | 0.18 | 312.63 (19.18×16.3) | Irregular | Undulate | Anomocytic | 97.15 | 0.09 | 357.39 (21.7×16.47) | 3.01 | 2 |
O. myriophylla | Polygonal | Straight arched | Anomocytic | 250.79 | 0.15 | 410.40 (21.83×18.8) | Polygonal | Straight arched | Anomocytic | 33.07 | 0.03 | 423.75 (23.82×17.79) | 7.58 | 5 |
O. aciphylla | Polygonal | Straight arched | Anomocytic | 369.29 | 0.16 | 253.77 (16.84×15.07) | Polygonal | Straight arched | Anomocytic | 234.94 | 0.11 | 257.21 (17.45×14.74) | 1.57 | 1.45 |
O. imbricata | Polygonal | Straight arched | Anomocytic | 139.17 | 0.14 | 409.05 (22.7×18.02) | Polygonal | Straight arched | Anomocytic | 81.3 | 0.11 | 372.01 (21.96×16.94) | 1.71 | 1.27 |
O. coerulea | Irregular | Sinuolate | Anomocytic | 152.95 | 0.21 | 526.83 (25.28×20.84) | Irregular | Sinuate | Anomocytic | 0.69 | 0.0031 | 514.8 (26.4×19.5) | 221.66 | 67.74 |
O. xinglongshanica | Polygonal | Straight arched | Anomocytic | 209.45 | 0.19 | 403.65 (21.89×18.44) | Polygonal | Straight arched | Anomocytic | 67.18 | 0.09 | 389.68 (21.03×18.53) | 3.11 | 2.11 |
O. glabra | Polygonal | Straight arched | Anomocytic | 173.62 | 0.25 | 442.83 (24.08×18.39) | Irregular | Undulate | Anomocytic | 92.32 | 0.21 | 517.17 (26.95×19.19) | 1.88 | 1.19 |
O. kansuensis | Polygonal | Straight arched | Anomocytic | 412.7 | 0.22 | 251.78 (17.87×14.09) | Irregular | Undulate | Anomocytic | 63.39 | 0.13 | 389.15 (22.25×17.49) | 6.51 | 1.69 |
O. melanocalyx | Polygonal | Straight arched | Anomocytic | 383.53 | 0.26 | 376.79 (21.73×17.34) | Irregular | Undulate | Anomocytic | 39.96 | 0.09 | 368.32 (22.68×16.24) | 9.59 | 2.88 |
O. taochensis | Polygonal | Straight arched | Anomocytic | 202.56 | 0.21 | 418.08 (23.37×17.89) | Irregular | Undulate | Anomocytic | 36.99 | 0.12 | 373.49 (21.88×17.07) | 5.47 | 1.75 |
O. ochrocephala (XLS) | Polygonal | Straight arched | Anomocytic | 265.95 | 0.2 | 388.29 (21.56×18.01) | Irregular | Sinuate | Anomocytic | 58.25 | 0.11 | 418.50 (22.72×18.42) | 4.56 | 1.81 |
O. ochrocephala (HZ) | Polygonal | Straight arched | Anomocytic | 289.37 | 0.21 | 419.94 (22.91×18.33) | Irregular | Sinuate | Anomocytic | 57.87 | 0.11 | 448.21 (23.64×18.96) | 5.0003 | 1.90 |
O. latibracteata | Irregular | Undulate | Anomocytic | 147.64 | 0.16 | 485.93 (24.53×19.81) | Irregular | Sinuate | Anomocytic | 93.21 | 0.1 | 544.02 (26.03×20.9) | 1.58 | 1.6 |
O. squammulosa | Irregular | Undulate | Anomocytic | 226.67 | 0.22 | 465.37 (22.58×20.61) | Irregular | Sinuate | Anomocytic | 99.9 | 0.15 | 542.38 (25.84×20.99) | 2.26 | 1.46 |
Light microscope photographs of epidermal cells in Oxytropis DC. A, B adaxial and abaxial epidermall cells of O. ciliata C, D adaxial and abaxial epidermall cells of O. muricata E, F adaxial and abaxial epidermall cells of O. falcata G, H adaxial and abaxial epidermall cells of O. ochrantha I, J adaxial and abaxial epidermall cells of O. bicolor K, L adaxial and abaxial epidermall cells of O. racemosa.
Light microscope photographs of epidermal cells in Oxytropis DC. A, B adaxial and abaxial epidermall cells of O. myriophylla C, D adaxial and abaxial epidermall cells of O. aciphylla E, F adaxial and abaxial epidermall cells of O. imbricata G, H adaxial and abaxial epidermall cells of O. coerulea I, J adaxial and abaxial epidermall cells of O. xinglongshanica K, L adaxial and abaxial epidermall cells of O. glabra.
In addition, SEM analysis showed that, based on the shape, the waxy layer on epidermal cells could be separated into three groups (Table
With respect to stomata, all species of Oxytropis studied here were anomocytic, and stomatal index (SI) and stomatal density (SD) of the adaxial epidermis were greater than those of the abaxial epidermis (Table
Light microscope photographs of epidermal cells in Oxytropis DC. A, B adaxial and abaxial epidermall cells of O. kansuensis C, D adaxial and abaxial epidermall cells of O. melanocalyx E, F adaxial and abaxial epidermall cells of O. taochensis G, H adaxial and abaxial epidermall cells of O. ochrocephala (XLS) I, J adaxial and abaxial epidermall cells of O. ochrocephala (HZ) K, L adaxial and abaxial epidermall cells of O. latibracteata M, N adaxial and abaxial epidermall cells of O. squammulosa.
Most of the species observed showed trichomes, except for O. squammulosa (Table
Characteristics of the leaf epidermis of Oxytropis under scanning electron microscopy.
Species | Adaxial epidermis | Abaxial epidermis | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
Shape of trichromes | Ornamentation of trichromes | Inner margin of outer stomatal ledge | Ornamentation of outer stomatal ledge | Waxy layer of epidermal cells | Shape of trichromes | Ornamentation of trichromes | Inner margin of outer stomatal ledge | Ornamentation of outer stomatal ledge | Waxy layer of epidermal cells | |
O. ciliata | strip-like | striation | undulate | smooth | smooth | absent | absent | smooth | smooth | smooth |
O. muricata | cylindrical | striation with granular | smooth | smooth | smooth | cylindrical | striation with granular | undulate | granular | granular |
O. falcata | cylindrical | striation with granular | undulate | granular | scale-like | cylindrical | striation with granular | undulate | granular | granular |
O. ochrantha | cylindrical | striation | undulate | smooth | granular | cylindrical | striation | smooth | smooth | smooth |
O. bicolor | cylindrical | striation with granular | smooth | smooth | smooth | cylindrical | striation with granular | smooth | smooth | smooth |
O. racemosa | cylindrical | striation with granular | undulate | granular | scale-like | cylindrical | striation with granular | undulate | granular | granular |
O. myriophylla | cylindrical | striation | undulate | granular | smooth | cylindrical | striation | undulate | granular | scale-like |
O. aciphylla | cylindrical | striation with granular | undulate | scale-like | scale-like | cylindrical | striation with granular | undulate | granular | granular |
O. imbricata | cylindrical | striation with granular | undulate | granular | granular | cylindrical | striation with granular | undulate | smooth | smooth |
O. coerulea | cylindrical | striation with granular | undulate | banded sediment | granular | absent | absent | undulate | banded sediment | granular |
O. xinglongshanica | cylindrical | striation with granular | undulate | scale-like | scale-like | cylindrical | striation with granular | undulate | scale-like | scale-like |
O. glabra | cylindrical | striation with granular | smooth | smooth | smooth | cylindrical | striation with granular | undulate | granular | granular |
O. kansuensis | cylindrical | striation with granular | undulate | granular | granular | cylindrical | striation with granular | undulate | granular | granular |
O. melanocalyx | cylindrical | striation with granular | undulate | scale-like | scale-like | cylindrical | striation with granular | undulate | smooth | smooth |
O. taochensis | cylindrical | striation with granular | undulate | scale-like | scale-like | cylindrical | striation with granular | undulate | granular | granular |
O. ochrocephala (XLS) | cylindrical | striation with granular | undulate | scale-like | scale-like | cylindrical | striation with granular | undulate | smooth | smooth |
O. ochrocephala (HZ) | cylindrical | striation with granular | undulate | scale-like | scale-like | cylindrical | striation with granular | undulate | smooth | smooth |
O. latibracteata | cylindrical | striation with granular | smooth | smooth | smooth | cylindrical | striation with granular | undulate | smooth | smooth |
O. squammulosa | absent | absent | undulate | granular | granular | absent | absent | undulate | granular | granular |
Scanning electron microscope photographs of epidermal cells in Oxytropis DC. A–C adaxial epidermall cells of O. ciliata D, E abaxial epidermall cells of O. ciliata F–H adaxial epidermall cells of O. muricata I–K abaxial epidermall cells of O. muricata L–N adaxial epidermall cells of O. falcata O–Q abaxial epidermall cells of O. falcata R–T adaxial epidermall cells of O. ochrantha. U–W abaxial epidermall cells of O. ochrantha X adaxial epidermall cells of O. bicolor.
Scanning electron microscope photographs of epidermal cells in Oxytropis DC. A, B adaxial epidermall cells of O. bicolor C–E abaxial epidermall cells of O. bicolor F–H adaxial epidermall cells of O. racemosa I–K abaxial epidermall cells of O. racemosa L–N adaxial epidermall cells of O. myriophylla O–Q abaxial epidermall cells of O. myriophylla R–T adaxial epidermall cells of O. aciphylla U–W abaxial epidermall cells of O. aciphylla X adaxial epidermall cells of O. imbricata.
Cluster analysis reflects the similarity among species based on anatomical characteristics and delimitation of these groups. The phenograms of the quantitative and qualitative data provided four principal clusters (Fig.
Scanning electron microscope photographs of epidermal cells in Oxytropis DC. A, B adaxial epidermall cells of O. imbricata C–E abaxial epidermall cells of O. imbricata F–H adaxial epidermall cells of O. coerulea I, J abaxial epidermall cells of O. coerulea K–M adaxial epidermall cells of O. xinglongshanica N–P abaxial epidermall cells of O. xinglongshanica Q–S adaxial epidermall cells of O. glabra T–V abaxial epidermall cells of O. glabra W–X adaxial epidermall cells of O. kansuensis.
Leaf characteristics, such as epidermal micro- and macro-hairs, and stomata, are important for the classification of many genera (
Scanning electron microscope photographs of epidermal cells in Oxytropis DC. A adaxial epidermall cells of O. kansuensis B–D abaxial epidermall cells of O. kansuensis E–G adaxial epidermall cells of O. melanocalyx H–J abaxial epidermall cells of O. melanocalyx K–M adaxial epidermall cells of O. taochensis N–P abaxial epidermall cells of O. taochensis Q–S adaxial epidermall cells of O. ochrocephala (HZ) T–V abaxial epidermall cells of O. ochrocephala (HZ) W–X adaxial epidermall cells of O. ochrocephala (XLS).
Studies on stomata can have great taxonomic significance for the delimitation of different levels of taxa (
Scanning electron microscope photographs of epidermal cells in Oxytropis DC. A adaxial epidermall cells of O. ochrocephala (XLS) B–D abaxial epidermall cells of O. ochrocephala (XLS) E–G adaxial epidermall cells of O. latibracteata H–J abaxial epidermall cells of O. latibracteata K–L adaxial epidermall cells of O. squammulosa M–N abaxial epidermall cells of O. squammulosa.
Further, trichomes and their characteristics provide important information for plant identification. The type of indumentum and its presence or absence may serve as diagnostic features for species or genus recognition, as has been recognized in some groups such as Asteraceae (
In this study, six species, including O. glabra, O. kansuensis, O. melanocalyx, O. taochensis, O. ochrocephala, and O. xinglongshanica, all belonging to section Mesogaea, clustered together. Our results of cluster analysis are largely consistent with that of the classification of species and sections based on macro morphological data (
There is no comprehensive phylogenetic study on the genus Oxytropis. Furthermore, although several studies have applied DNA barcodes such as ITS, trnL-F, and psbA-trnH to explore the molecular phylogeny of Oxytropis in Northwestern China, the low genetic divergence of the above barcodes among the species makes it difficult to distinguish species within the genus as well as to resolve phylogenetic relationships between sections (
Our results suggest that leaf epidermis can be used as potential taxonomic markers for infrageneric classification of Oxytropis. The shape of epidermal cells and the pattern of the anticlinal wall were constant within species, and are useful for species delimitation in the genus Oxytropis when combined with other macroscopic traits. Trichome shapes can be useful characteristics to distinguish O. ciliata from other investigated species. Although quantitative stomatal characteristics were not effective diagnostic characteristics because of the considerable variation within the same taxa, it nevertheless plays an important role in cluster analysis. Results of cluster analysis are largely consistent with the classification of species and sections based on macro morphological data, indicating that foliar epidermis characteristics of Oxytropis can be used as taxonomic identification markers infrageneric classification level. Lastly, our results support the delineation of the sect. Leucopodia as an independent section, while not supporting the treatment of merging the sect. Gobicola into the sect. Baicalia.
The author thanks Dr. Xiaowei Li and Mr. Xiaoxu Lyu for their help in collecting specimens in the field. Author contributions: Xiang Zhao: Conceptualization, Methodology, Sample collection, Laboratory analysis, Data analysis, Validation, Data curation, Writing-Original draft preparation. Qinzheng Hou: Methodology, Data analysis, Validation, Writing-Reviewing and Editing, Visualization. Meina Du: Sample collection, Visualization. Hui Zhang: Sample collection. Lingyun Jia: Laboratory analysis. Zhihua Zhang: Laboratory analysis. Zongqi Ma: Laboratory analysis. Kun Sun: Conceptualization, Methodology, Writing-Reviewing and Editing, Supervision, Project administration. This work was supported by the Gansu Key Research and Development Project-Agriculture (grant number 18YF1NA051)