Research Article |
Corresponding author: Dunyan Tan ( tandunyan@163.com ) Academic editor: Lorenzo Peruzzi
© 2023 Musen Lin, Juan Qiu, Kaiqing Xie, Dunyan Tan.
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:
Lin M, Qiu J, Xie K, Tan D (2023) Palynological features and taxonomic significance for 16 species of Gagea (Liliaceae) from Xinjiang, China. PhytoKeys 225: 53-68. https://doi.org/10.3897/phytokeys.225.101518
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Since pollen characters can be used to help distinguish species, our aim was to determine if palynological information has taxonomic significance for Gagea species from Xinjiang, China. Gagea is widely distributed in north temperate and the subtropical zones. The genus has limited taxonomic characteristics and large morphological variation, which results in difficulty of species classification. Pollen morphology of 16 species of this genus was examined comprehensively via light microscope (LM) and scanning electron microscope (SEM). One qualitative and nine quantitative traits of the pollen grains were surveyed, followed by hierarchical cluster analysis (HCA). The pollen grains were bilaterally symmetrical heteropolar monads with a mono-sulcus and they were oblate or peroblate (Polar diameter (P) / Equatorial diameter (E) = 0.36–0.73) in shape and medium to large (P = 17.17–34.64 μm, E = 27.63–81.65 μm) in size. Three types of exine ornamentation were observed: perforate, microreticulate and reticulate cristatum. The HCA divided the 16 species into two groups. This research provides new data on pollen morphology for Gagea (the pollen morphology of eight species was reported for the first time). Pollen morphology also can be used to identify species with similar external morphology, such as G. nigra and G. filiformis. Furthermore, the study of pollen morphology not only provides new data for palynology research on Gagea, but also provides a basis for future classification of this genus.
HCA, pollen morphology, SEM, taxonomy
Pollen morphology is scarcely affected by ecological conditions; thus, it is more stable than external macrographical morphology and has high genetic stability (
Gagea Salisb. (
The initial phylogenetic analysis of Gagea was conducted in 2008 (
The Flora of China includes 17 species of Gagea (
At present, the pollen morphology of 46 species in Gagea has been described by various researchers from different regions in the world (
Through extensive field investigations in Xinjiang, we have found that G. nigra is similar to G. filiformis. The most salient resemblance characters were observed in G. nigra and G. filiformis, such as ovoid-globose bulb, brown or black tunic, leaf and flower number, umbellate or corymbose inflorescence, yellow tepals, capitate stigma, obovoid capsule and red-brown, ovoid-globose seeds. Furthermore, G. jensii shared morphological characters with G. altaica and G. alberti, including ovoid bulbs, taupe tunic, cauline leaves, corymbose or racemose inflorescence, yellow tepals, slightly 3-lobed stigma and brown flat seeds. Hence, the purpose of this research is to: (1) provide palynological information for 16 species of Gagea from Xinjiang, China, using a light microscope (LM) and scanning electron microscope (SEM); (2) distinguish species with similar morphology using palynological characters; and (3) explain the taxonomic significance of palynology in Gagea.
During April-July 2020–2022, a field investigation was carried out in Xinjiang, China, including the Altai Mountains, Tien-Shan Mountains, Kunlun Mountains and Junggar Basin to collect samples of pollen. Pollen collections were made from a total of 60 populations of the 16 Gagea species in Xinjiang. For widespread species (such as G. bulbifera, G. fedtschenkoana and G. nigra) at least five populations were included in this research. If there were no differences in pollen morphology amongst the populations of a species, one population was selected as a representative for SEM. If populations of a species varied, separate studies were conducted on all of the populations for the species.
The species were identified after collection by comparing their morphological characteristics to those listed in Flora of China (
The list of materials for scanning electron microscope and vouchers of 16 species of Gagea from Xinjiang, China.
Species | Section ( |
Locality | Coordinate | Altitude | Collection Date | Voucher |
---|---|---|---|---|---|---|
Gagea alberti Regel | Plecostigma | Shihezi City, Xinjiang, China | 44.188091°N, 86.088827°E | 517 m | 12 April 2022 | J.Qiu & J.L.Li L-034 ( |
G. altaica Schischk. & Sumnev. | Plecostigma | Fuyun County, Xinjiang, China | 46.368831°N, 88.926181°E | 777 m | 15 April 2021 | J.Qiu & M.S.Lin L-006 ( |
G. angelae Levichev & Schnittler | Gagea | Gongliu County, Xinjiang, China | 43.110484°N, 82.751261°E | 1660 m | 4 May 2021 | J.C.Chi Chijc4473 ( |
G. bulbifera (Pall.) Salisb. | Bulbiferae | Shawan County, Xinjiang, China | 45.328851°N, 88.455975°E | 561 m | 7 April 2021 | J.Qiu & M.S.Lin L-002 ( |
G. divaricata Regel | Platyspermum | Fukang City, Xinjiang, China | 44.739223°N, 88.270266°E | 616m | 17 April 2021 | J.Qiu & M.S.Lin L-011 ( |
G. fedtschenkoana Pascher | Gagea | Qinghe County, Xinjiang, China | 46.746946°N, 90.873269°E | 2761 m | 6 June 2021 | J.Qiu & M.S.Lin L-018 ( |
G. filiformis (Ledeb.) Kar. & Kir. | Minimae | Ürümqi City, Xinjiang, China | 43.786772°N, 87.565508°E | 1075 m | 3 April 2021 | J.Qiu & M.S.Lin L-004 ( |
G. fragifera (Vill.) E.Bayer & G.López | Didymobolbos | Burqin City, Xinjiang, China | 48.429559°N, 87.207309°E | 1988 m | 9 June 2021 | J.Qiu & M.S.Lin L-021 ( |
G. granulosa Turcz. | Minimae | Burqin City, Xinjiang, China | 48.429694°N, 87.207108°E | 1984 m | 9 June 2021 | J.Qiu & M.S.Lin L-023 ( |
G. jaeschkei Pascher | Bulbiferae | Qapqal County, Xinjiang, China | 43.411647°N, 81.040648°E | 2929 m | 17 July 2021 | J.Qiu & M.S.Lin L-30 ( |
G. jensii Levichev & Schnittler | Plecostigma | Ürümqi City, Xinjiang, China | 43.783443°N, 87.544818°E | 1002 m | 8 April 2021 | J.Qiu & M.S.Lin L-005 ( |
G. nigra L.Z.Shue | Minimae | Ürümqi City, Xinjiang, China | 43.783141°N, 87.544363°E | 995 m | 2 April 2021 | J.Qiu & M.S.Lin L-003 ( |
G. neopopovii Golosk. | Plecostigma | Huocheng County, Xinjiang, China | 44.483283°N, 81.175174°E | 2100 m | 19 May 2021 | X.J. Ge Gexj-21019 ( |
G. kunawurensis (Royle) Greuter | Dschungaricae | Ürümqi City, Xinjiang, China | 43.785813°N, 87.545323°E | 997 m | 20 April 2021 | J.Qiu & M.S.Lin L-015 ( |
G. stepposa L.Z.Shue | Bulbiferae | Ürümqi County, Xinjiang, China | 43.516102°N, 87.447984°E | 1559 m | 10 April 2022 | J.Qiu & J.L.Li L-032 ( |
G. tenera Pascher | Didymobolbos | Nilka County, Xinjiang, China | 43.724538°N, 82.070252°E | 1033 m | 22 April 2022 | J.Qiu & J.L.Li L-041 ( |
All pollen grains were taken from fresh flowers, except for G. angelae and G. neopopovii, which were obtained from herbarium specimens. At peak flowering in each natural population, five individual plants were selected for pollen collection. Mature anthers were removed before dehiscence and placed in a clean glass bottle for natural drying.
Pollen slides were prepared following standard methods (
A label that referred to the number of the voucher specimen was attached to each slide. Pollen grains were photographed under LM (Nikon Eclipse 80i) at a magnification of 40× and SEM (Zeiss SUPRA 55VP) at an accelerating voltage of 2 kV. Each species/ population observed the polar diameter (P) and equatorial diameter (E) of 30 pollen grains under LM with an immersion objective lens (at 100× magnification). The microscopic morphological features of pollen [colpus width (Clt), colpus length (Clg), porus width (Plt), porus length (Plg), exine thickness (Ex), intine thickness (In) and ornamentation] were measured under SEM.
The results of palynological measurements were evaluated by statistical analysis and the contribution of each variable to the classification of each investigated was determined.
A one-way ANOVA was used to determine differences in pollen morphology of different populations of the same species. Prior to the analysis, the SPSS programme version 26 was used to test for normality and homogeneity of variance to satisfy the requirements of one-way analysis of variance (ANOVA). Differences amongst species were determined by the non-parametric Kruskal-Wallis test.
One qualitative (ornamentation) and nine quantitative palynological variables (polar diameter, equatorial diameter, P/ E, porus length, porus width, colpus length, colpus width, exine thickness and intine thickness) were evaluated in the comparative analysis for their value in distinguishing the studied Gagea species. Quantitative variables were represented by minimum (mean ± standard error) and maximum (for example: 20.34 (20.64 ± 0.24) 21.12 μm), whereas qualitative variables were recorded in the data matrix as 0, 1 or 2. Origin 2021 software was adopted for hierarchical cluster analysis (HCA) on Gagea pollen data. Euclidean distances of the stem were calculated after Z-score normalizing the original data and they were clustered using Ward’s method (
Within populations of each species, pollen shape and exine ornamentation were stable, but the size of pollen grains was not. One-way ANOVA showed that the means of equatorial diameter were not significantly different amongst populations of the same species (p > 0.05). Nevertheless, there was a significant difference in mean equatorial diameter amongst different species (H = 378.016, df = 15, p < 0.001). Therefore, a random population was selected as a representative material for each species for SEM and the micro-morphological characters of pollen grains were carefully observed.
In general, pollen grains of the Gagea species were similar in their morphological characters. The detailed pollen morphology data for the 16 species of Gagea are summarised in Table
Species | P (μm) Min (Mean ± SE) Max | E (μm) Min (Mean ± SE) Max | P/E | Plg (μm) Min (Mean ± SE) Max | Plt (μm) Min (Mean ± SE) Max |
---|---|---|---|---|---|
Gagea alberti | 20.34 (20.64±0.24) 21.12 | 42.77 (45.73±1.85) 49.14 | 0.45 | 0.28 (0.39±0.05) 0.72 | 0.24 (0.37±0.03) 0.57 |
G. altaica | 27.93 (29.34±0.55) 30.61 | 57.32 (62.41±3.69) 73.36 | 0.47 | 0.24 (0.39±0.03) 0.58 | 0.21 (0.37±0.03) 0.49 |
G. angelae | 26.38 (28.18±1.07) 30.07 | 71.97 (78.14±3.09) 81.65 | 0.36 | 0.46 (0.75±0.06) 1.04 | 0.42 (0.57±0.03) 0.71 |
G. bulbifera | 26.28 (30.92±0.92) 34.64 | 36.73 (42.71±1.34) 51.34 | 0.73 | 0.16 (0.50±0.02) 0.49 | 0.14 (0.37±0.03) 0.43 |
G. divaricata | 28.11 (28.56±0.40) 29.36 | 46.30 (56.86±5.30) 62.91 | 0.49 | 0.58 (0.72±0.08) 0.94 | 0.54 (0.68±0.11) 1.10 |
G. fedtschenkoana | 22.37 (22.74±0.19) 23.02 | 49.12 (58.22±5.52) 68.18 | 0.41 | 0.13 (0.36±0.09) 0.62 | 0.13 (0.23±0.03) 0.33 |
G. filiformis | 23.72 (24.58±0.41) 25.75 | 58.94 (62.60±2.21) 71.08 | 0.39 | 0.36 (0.45±0.05) 0.56 | 0.28 (0.40±0.06) 0.54 |
G. fragifera | 20.98 (23.78±1.41) 25.50 | 62.22 (65.61±2.01) 69.16 | 0.36 | 0.44 (0.53±0.03) 0.63 | 0.29 (0.39±0.04) 0.50 |
G. granulosa | 19.58 (25.50±2.96) 28.63 | 49.84 (51.89±1.04) 53.23 | 0.49 | 0.19 (0.30±0.02) 0.36 | 0.15 (0.22±0.02) 0.32 |
G. jaeschkei | 15.07 (20.10±2.65) 29.43 | 33.36 (37.53±1.11) 39.43 | 0.54 | 0.12 (0.20±0.02) 0.26 | 0.06 (0.14±0.02) 0.26 |
G. jensii | 22.86 (23.28±0.82) 25.80 | 46.89 (53.34±2.63) 62.16 | 0.44 | 0.13 (0.22±0.03) 0.44 | 0.10 (0.18±0.02) 0.33 |
G. neopopovii | 17.17 (22.15±0.99) 26.13 | 27.63 (44.79±4.32) 66.88 | 0.54 | 0.30 (0.44±0.02) 0.69 | 0.15 (0.31±0.02) 0.62 |
G. nigra | 20.26 (22.50±1.16) 24.14 | 41.77 (51.41±4.86) 57.35 | 0.45 | 0.27 (0.38±0.06) 0.55 | 0.13 (0.34±0.05) 0.42 |
G. kunawurensis | 21.92 (23.58±0.88) 24.94 | 50.66 (56.82±3.20) 61.42 | 0.41 | 0.58 (0.78±0.05) 1.00 | 0.43 (0.64±0.03) 0.76 |
G. stepposa | 25.31 (26.15±0.43) 26.68 | 58.51 (61.87±1.90) 65.10 | 0.42 | 0.28 (0.46±0.05) 0.73 | 0.17 (0.39±0.05) 0.63 |
G. tenera | 18.34 (23.14±2.43) 29.17 | 42.89 (48.63±3.47) 58.31 | 0.47 | 0.28 (0.43±0.04) 0.63 | 0.18 (0.33±0.04) 0.52 |
Species | Clg (μm) Min (Mean ± SE) Max | Clt (μm) Min (Mean ± SE) Max | Ex (μm) Min (Mean ± SE) Max | In (μm) Min (Mean ± SE) Max | Ornamentation |
Gagea alberti | 41.35 (44.38±1.95) 48.02 | 1.67 (1.95±0.19) 2.32 | 0.93 (1.57±0.18) 2.93 | 0.50 (0.90±0.09) 1.45 | Perforate (0) |
G. altaica | 56.01 (60.35±3.36) 70.38 | 3.25 (3.61±0.38) 4.01 | 0.81 (1.59±0.07) 2.08 | 0.58 (0.97±0.04) 1.39 | Microreticulate (1) |
G. angelae | 69.65 (75.38±2.87) 78.32 | 0.87 (1.60±0.47) 2.48 | 0.88 (1.83±0.12) 2.42 | 0.61 (0.99±0.05) 1.29 | Reticulate cristatum (2) |
G. bulbifera | 36.47 (42.05±2.02) 48.24 | 1.71 (2.14±0.23) 2.78 | 1.41 (1.90±0.08) 2.63 | 0.78 (1.16±0.07) 1.93 | Microreticulate (1) |
G. divaricata | 43.60 (53.08±4.74) 57.84 | 3.74 (3.95±0.19) 4.33 | 1.11 (1.65±0.08) 2.26 | 0.51 (0.81±0.06) 1.42 | Reticulate cristatum (2) |
G. fedtschenkoana | 47.10 (56.07±5.62) 66.42 | 1.51 (1.60±0.06) 1.71 | 1.32 (1.77±0.07) 2.17 | 0.72 (0.92±0.03) 1.14 | Microreticulate (1) |
G. filiformis | 55.51 (59.02±2.45) 68.68 | 1.96 (2.17±0.13) 2.71 | 0.47 (1.41±0.12) 2.35 | 0.28 (0.75±0.06) 1.14 | Microreticulate (1) |
G. fragifera | 57.64 (61.54±2.80) 66.98 | 1.85 (2.00±0.08) 2.12 | 0.76 (1.66±0.11) 2.16 | 0.39 (0.87±0.06) 1.38 | Reticulate cristatum (2) |
G. granulosa | 46.19 (49.36±1.62) 51.54 | 2.04 (2.70±0.56) 3.81 | 1.72 (2.30±0.10) 2.73 | 0.94 (1.23±0.06) 1.57 | Perforate (0) |
G. jaeschkei | 30.47 (34.31±1.01) 36.46 | 0.73 (1.54±0.27) 2.36 | 1.02 (1.94±0.13) 2.36 | 0.56 (1.04±0.08) 1.40 | Perforate (0) |
G. jensii | 44.45 (51.18±2.70) 60.38 | 1.64 (2.59±0.29) 3.09 | 1.22 (1.49±0.18) 2.18 | 0.76 (1.06±0.14) 1.57 | Perforate (0) |
G. neopopovii | 24.98 (41.03±4.53) 63.26 | 1.13 (1.30±0.06) 1.83 | 1.00 (1.79±0.20) 2.70 | 0.64 (1.04±0.14) 1.57 | Reticulate cristatum (2) |
G. nigra | 39.05 (48.80±4.97) 55.39 | 0.92 (1.24±0.30) 1.85 | 1.12 (1.59±0.09) 2.24 | 0.53 (0.83±0.05) 1.12 | Reticulate cristatum (2) |
G. kunawurensis | 48.20 (54.48±3.34) 59.61 | 1.18 (1.62±0.33) 2.26 | 1.34 (1.97±0.08) 2.51 | 0.78 (1.14±0.05) 1.46 | Reticulate cristatum (2) |
G. stepposa | 57.46 (60.59±1.67) 63.19 | 2.30 (2.55±0.14) 2.78 | 0.66 (1.31±0.10) 1.85 | 0.27 (0.72±0.07) 1.32 | Microreticulate (1) |
G. tenera | 38.48 (44.19±3.38) 53.58 | 0.54 (1.01±0.30) 1.87 | 1.08 (2.10±0.13) 2.89 | 0.44 (1.07±0.08) 1.48 | Reticulate cristatum (2) |
Pollen grains of all species were heteropolar monads and they were mono-sulcus, bilaterally symmetrical and ellipsoidal in polar view. Pollen shape was oblate (Figs
Light microscope micrographs of pollen grains of eight species of Gagea from Xinjiang, China A, A1 Gagea alberti B, B1 G. altaica C, C1 G. angelae D, D1 G. bulbifera E, E1 G. divaricata F, F1 G. fedtschenkoana G, G1 G. filiformis H, H1 G. fragifera. A–H Pollen grain in polar view A1–H1 Pollen grain in equatorial view. Scale bars: 10 μm.
Light microscope micrographs of pollen grains of eight species of Gagea from Xinjiang, China. I, I1 Gagea granulosa J, J1 G. jaeschkei K, K1 G. jensii L, L1 G. neopopovii M, M1 G. nigra N, N1 G. kunawurensis O, O1 G. stepposa P, P1 G. tenera. I–P Pollen grain in polar view. I1–P1 Pollen grain in equatorial view. Scale bars: 10 μm.
Pollen grains in polar view (A–H) and exine ornamentation (A1–H1) under scanning electron microscope for eight species of Gagea from Xinjiang, China A, A1 Gagea alberti B, B1 G. altaica C, C1 G. angelae D, D1 G. bulbifera E, E1 G. divaricata F, F1 G. fedtschenkoana G, G1 G. filiformis H, H1 G. fragifera.
Pollen grains in polar view (I–P) and exine ornamentation (I1–P1) under scanning electron microscope for eight species of Gagea from Xinjiang, China I, I1 Gagea granulosa J, J1 G. jaeschkei K, K1 G. jensii L, L1 G. neopopovii M, M1 G. nigra N, N1 G. kunawurensis O, O1 G. stepposa P, P1 G. tenera.
Thickness of the pollen exine and intine of all species was similar, ranging from 1.31 ± 0.10 to 2.3 ± 0.1 μm and from 0.72 ± 0.07 to 1.23 ± 0.06 μm, respectively. Only G. stepposa had a thinner exine than the other species (Table
Three types of pollen grain exine ornamentation were identified: type I, Perforate (Figs
In type I, exine ornamentation had gemmate protuberances. Perforations were smaller than muri and observed throughout the pollen grains. This type was found in G. alberti, G. granulosa, G. jaeschkei and G. jensii. The smallest pollen grains were in G. jaeschkei with a size (i.e. polar diameter × equatorial diameter) of 20.10 ± 2.65 × 37.53 ± 1.11 μm and the largest pollen grains in G. jensii with a size of 23.28 ± 0.82 × 53.34 ± 2.63 μm.
In type II, lumina were not similar in diameter and they were as wide as the muri or smaller than the muri. Muri were complete or compound and the width was narrow from the proximal to distal surface. This type was found in G. altaica, G. bulbifera, G. fedtschenkoana, G. filiformis and G. stepposa. The smallest pollen grains were discovered in G. bulbifera with a size of 30.92 ± 0.92 × 42.71 ± 1.34 μm and the largest pollen grains in G. filiformis with a size of 24.58 ± 0.41 × 62.6 ± 2.21 μm.
In type III, lumina were similar in diameter, they were as wide as the muri or wider than the muri. Muri had regular prominent croton pattern or gemmate suprasculpture. Type III was found in G. angelae, G. divaricata, G. fragifera, G. neopopovii, G. nigra, G. kunawurensis and G. tenera. The smallest pollen grains were for G. neopopovii with a size of 22.15 ± 0.99 × 44.79 ± 4.32 μm and the largest pollen grains in G. angelae with a size of 28.18 ± 1.07 × 78.14 ± 3.09 μm.
The palynological groups of the species, based on their relevance, were evaluated by hierarchical cluster analysis. In this analysis, pollen morphology separated the Gagea species into two groups, based on Euclidean distance of 7.01. Group A included G. alberti, G. bulbifera, G. granulosa, G. jaeschkei, G. jensii, G. neopopovii and G. tenera. It was arranged into two subgroups (A1 and A2), based on Euclidean distance of 5.95. Whereas group B involved G. altaica, G. angelae, G. divaricata, G. fedtschenkoana, G. filiformis, G. fragifera, G. kunawurensis, G. nigra and G. stepposa (Fig.
Our results supported previous research showing that the pollen grains in Gagea were bilaterally symmetrical heteropolar monads with a mono-sulcus (
Pollen morphology of five Gagea species (G. alberti, G. bulbifera, G. fedtschenkoana, G. granulosa and G. nigra) collected from Xinjiang have been described (
Pollen characters have been employed as useful morphological features for the identification of species or genera and they have been applied widely to Allium (
Information on palynology should be used to provide new insight into the differences (or not) between species. For example, in the revision of G. nigra by
According to recent infrageneric classification of Gagea, the species in this research belong to seven sections (Table
Gagea nigra and G. filiformis belong to the sect. Minimae, and morphology and molecular evidence suggest that G. nigra is an independent species separated from G. filiformis (
Although the results are not able to offer a diagnostic key amongst groups of Gagea taxa in Xinjiang, China, they demonstrate that palynology may aid in the taxonomy of the genus by differentiating between taxa within their groups.
Pollen morphology of eight species of Gagea from Xinjiang, China was reported for the first time in our research. Gagea pollen grains were heterogenous in shape, size and exine ornamentation. Pollen characters have a certain taxonomic effect on the interspecies of Gagea, but the taxonomic relationship cannot be fully clarified only by pollen morphology. The results of the current research have provided palynological data for the classification of Gagea and also contribute to future classification of this genus.
We thank Dr Carol C. Baskin (University of Kentucky, Lexington, Kentucky, USA) for correcting the English and we are grateful to Jiancai Chi for collecting G. angelae. We also thank the Xinjiang Institute of Ecology and Geography Chinese Academy of Sciences Herbarium (XJBI) and Yang’s Herbarium for providing specimens.
This research was supported by the Natural Science Foundation of Xinjiang Uygur Autonomous Region, China (2022D01A71), the Grant of Innovation Environment Construction of the Xinjiang Uygur Autonomous Region, China (PT2224), the Innovative Team Foundation of Biology of Xinjiang Agricultural University, China (ITB202103) and the Xinjiang Agricultural University Graduate Research and Innovation Project (XJAUGRI2022042).
Species collection table and a one-way ANOVA results of species with more than two populations
Data type: pdf file