Research Article |
Corresponding author: Erandi Sánchez-Chávez ( erandi.sanchez4@gmail.com ) Academic editor: Alexander Sennikov
© 2022 Erandi Sánchez-Chávez, Andrew Vovides, Victoria Sosa.
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:
Sánchez-Chávez E, Vovides A, Sosa V (2022) Pollen morphology of the genera Hidalgoa and Dahlia (Coreopsideae, Asteraceae): implications for taxonomy. PhytoKeys 199: 187-202. https://doi.org/10.3897/phytokeys.199.79501
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Hidalgoa and Dahlia are two closely related genera in Asteraceae, tribe Coreopsideae whose limits need to be clarified. Pollen morphology has been useful for delimitation at the genus level in this family. To better define these genera, the morphology of pollen grains was observed and measured using light and scanning electron microscopy. The pollen grains of 25 species of Dahlia and Hidalgoa were acetolyzed and analyzed. Pollen is tricorporate in most of the species studied, although in a few species in Dahlia, grains were found to be hexacolporate. The most outstanding differentiating characters among species of Dahlia and Hidalgoa are colpus length (greater in Hidalgoa) and shape of spines (conical in Hidalgoa). In addition, lalongate ora are larger in Hidalgoa than in Dahlia. A PCA analysis of thirteen pollen characters, identified species of Hidalgoa in a discrete group and Dahlia cuspidata as an outlier. These distinctive attributes in pollen morphology support the idea that pollen morphology is useful for delimitation at the generic level in the Dahlia clade. Further evidence from other sources, genetic or anatomical, might contribute to demarcating Dahlia and Hidalgoa, and provide insight into the family’s evolutionary history.
Asteraceae, Dahlia, hexacolporate, Hidalgoa, pollen morphology, tricolporate
Hidalgoa La Llave and Dahlia Cav. are two closely related genera in tribe Coreopsideae of the Asteraceae (
Dahlia includes 40 species, of which 37 are endemic to Mexico (
Hidalgoa was thought to be closely related to the genera Fitchia Hook. f, Moonia Arn., Oparanthus Sherff, and Petrobium R. Br., for sharing the character of functional male disc florets (
In spite of the uniform pollen morphology in the genera of Asteraceae, some pollen characters have been shown to be useful for supporting recognition and delimitation in numerous genera (
The pollen in tribe Coreopsideae is helianthoid (exine with columellae containing internal foramina and clearly caveate), predominantly spheroidal, tricolporate, echinate, with internal foramina, full cavea present, and endexine much thicker than the foot layer (
Pollen morphology has not been analyzed in detail for the species of Hidalgoa or Dahlia. Previous palynological research by
The aims of this study are to compile and compare pollen morphology of the species of Hidalgoa and Dahlia to identify informative characters and understand the relationships and limits of these taxa.
Twenty-five samples of pollen grains were obtained from herbarium specimens deposited in the
Studied species of Hidalgoa and Dahlia for analyzing pollen grains, indicating their voucher and the herbarium in which they were deposited. Herbarium acronyms are according to Index Herbariorum.
Species | Locality | Collector | Herbarium |
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Dahlia atropurpurea P.D. Sørensen | Guerrero | A. Castro C. 2251 |
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Dahlia australis (Sherff) P.D. Sørensen | Puebla | A. Rodriguez C. 6491 |
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Dahlia barkerae Knowles & Westc. | Jalisco | A. Castro C. 2304 |
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Dahlia brevis P.D. Sørensen | México | A. Rodriguez C. 5869 |
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Dahlia campanulata Saar, P.D. Sørensen & Hjert. | Oaxaca | A. Rodriguez C. 6495 |
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Dahlia coccinea Cav. | Jalisco | A. Rodriguez C. 7490 |
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Dahlia cordifolia (Sessé & Moc.) McVaugh | Guerrero | A. Rodriguez C. 5224 |
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Dahlia cuspidata Saar, P.D. Sørensen & Hjert. | Guanajuato | E. Ventura 9581 |
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Dahlia dissecta S. Watson | A. Rodriguez C. 6412 |
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Dahlia imperialis Roezl ex Ortgies | Chiapas | A. Rodriguez C. 6983 |
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Dahlia linearis Sherff | Guanajuato | E. Ventura 6143 |
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Dahlia merckii Lehm. | L. Gutierrez s/n |
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Dahlia mollis P.D. Sørensen | Hidalgo | A. Rodriguez C. 6414 |
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Dahlia neglecta Saar | Hidalgo | A. Rodriguez C. 6466 |
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Dahlia parvibracteata Saar & P.D. Sørensen | Guerrero | A. Rodriguez C. 6092 |
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Dahlia pugana Aarón Rodr. & Art. Castro | Jalisco | A. Rodriguez C. 7731 |
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Dahlia rudis P.D. Sørensen | A. Ma. Hernández 12 |
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Dahlia rupicola P.D. Sørensen | Durango | A. Rodriguez C. 6133 |
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Dahlia scapigera Knowles & Westc. | Queretaro | E. Gonzalez P. 560 |
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Dahlia sorensenii H.V. Hansen & Hjert. | J. Suárez J. 584 |
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Dahlia spectabilis Saar & P.D. Sørensen | San Luis Potosí | A. Rodriguez C. 6352 |
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Dahlia tenuicaulis P.D. Sørensen | Jalisco | M. Chazaro B. 5736 |
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Dahlia wixarika Art. Castro, Carr.-Ortiz & Aarón Rodr. | Jalisco | A. Castro C. 2983 |
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Hidalgoa pentamera Sherff | Veracruz | E. Sánchez-Chávez 28 |
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Hidalgoa ternata La Llave | Veracruz | T. B. Croat 25505 |
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Pollen grains were acetolyzed according to the methodology of
To observe the pollen with a scanning electron microscope (SEM), acetolyzed pollen grains were washed in ethanol and later in water. Grains were sputter-coated with gold and observed using a Carl Zeiss EVO-50 scanning electron microscope. The terminology of
Pollen attributes analyzed on the studied species of Hidalgoa and Dahlia. The values given in exine, colpus, ora, spine are averages. Cl colpus length, Cw colpus width, Ow Os width, Ol Os length, Swab Width at base.
Specie | Polar axis (P)(μm) | Equatorial diameter (E)(μm) | P/E | Pollen shape | Number of apertures | Exine (μm) | Colpus (μm) | Os (μm) | Spine | Number of spines/100 μm2 | Base of spine | ||||||||
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Min | Max | Mean | Min | Max | Mean | Cl | Cw | Copus ends | Osl | Ow | Length (μm) | Swab (μm) | |||||||
Dahlia atropurpurea | 28.18 | 32.70 | 30.43 | 28.85 | 32.46 | 30.92 | 0.98 | Oblate-spheroidal | Tricolporate | 2.88 | 3.79 | 3.12 | acute | 2.28 | 2.55 | 7.80 | 5.99 | 7–8 | distended |
Dahlia australis | 25.38 | 29.98 | 28.43 | 23.88 | 30.49 | 28.32 | 1.00 | Spheroidal | Tricolporate | 2.63 | 3.01 | 3.08 | acute | 2.56 | 2.05 | 6.01 | 4.51 | 6–8 | distended |
Dahlia barkerae | 30.62 | 36.15 | 33.78 | 30.86 | 34.82 | 33.34 | 1.01 | Prolate-spheroidal | Tricolporate | 3.58 | 6.38 | 5.63 | acute | 2.20 | 3.09 | 7.55 | 7.21 | 4–5 | distended |
Dahlia brevis | 26.41 | 32.33 | 29.04 | 25.53 | 32.58 | 29.41 | 0.99 | Oblate-spheroidal | Tricolporate | 1.81 | 4.83 | 4.74 | obtuse | 2.06 | 2.93 | 7.37 | 5.79 | 7–10 | distended |
Dahlia campanulata | 30.61 | 34.72 | 32.84 | 30.50 | 34.48 | 32.96 | 1.00 | Spheroidal | Tricolporate | 2.24 | 4.34 | 1.54 | obtuse | 1.44 | 1.92 | 7.35 | 6.99 | 5–7 | smooth |
Dahlia coccinea | 29.42 | 39.47 | 34.74 | 31.66 | 39.83 | 34.79 | 1.00 | Spheroidal | Tricolporate | 3.05 | 5.42 | 4.53 | obtuse | 3.18 | 2.71 | 9.81 | 8.17 | 4–5 | distended |
Dahlia cordifolia | 27.80 | 32.03 | 29.64 | 28.00 | 33.46 | 30.61 | 0.97 | Oblate-spheroidal | Tricolporate | 2.96 | 5.75 | 4.26 | obtuse | 2.32 | 2.74 | 7.87 | 6.64 | 6–7 | smooth |
Dahlia cuspidata | 31.21 | 35.48 | 33.16 | 31.63 | 37.05 | 34.44 | 0.96 | Oblate-spheroidal | Hexacolporate/ Tricolporate | 1.64 | 8.61 | 6.22 | obtuse | 4.75 | 5.24 | 9.07 | 6.94 | 4–6 | distended |
Dahlia dissecta | 28.34 | 32.50 | 30.55 | 27.72 | 32.21 | 30.31 | 1.01 | Prolate-spheroidal | Hexacolporate/ Tricolporate | 2.88 | 3.80 | 2.95 | obtuse | 2.18 | 2.35 | 7.33 | 6.57 | 5–7 | smooth |
Dahlia imperialis | 25.95 | 30.64 | 28.04 | 25.78 | 31.50 | 28.94 | 0.97 | Oblate-spheroidal | Hexacolporate/ Tricolporate | 1.98 | 3.85 | 2.93 | obtuse | 2.17 | 2.93 | 7.46 | 5.95 | 6–8 | smooth |
Dahlia linearis | 29.83 | 33.79 | 31.82 | 29.85 | 34.99 | 32.68 | 0.97 | Oblate-spheroidal | Tricolporate | 2.19 | 3.98 | 4.44 | obtuse | 2.42 | 3.70 | 5.29 | 5.59 | 8–10 | smooth |
Dahlia merckii | 26.19 | 31.65 | 28.54 | 28.64 | 34.78 | 31.61 | 0.90 | Oblate-spheroidal | Hexacolporate/ Tricolporate | 3.05 | 4.59 | 3.16 | obtuse | 1.45 | 2.75 | 6.97 | 6.25 | 7–8 | distended |
Dahlia mollis | 26.59 | 30.26 | 28.38 | 28.14 | 32.36 | 29.93 | 0.95 | Oblate-spheroidal | Tricolporate | 1.88 | 4.14 | 2.42 | obtuse | 2.20 | 2.42 | 7.79 | 6.27 | 5–7 | distended |
Dahlia neglecta | 32.72 | 37.48 | 35.06 | 30.75 | 37.77 | 35.77 | 0.98 | Oblate-spheroidal | Tricolporate | 4.20 | 4.81 | 3.34 | obtuse | 2.35 | 3.03 | 6.82 | 6.80 | 4–5 | distended |
Dahlia parvibracteata | 29.58 | 32.88 | 31.29 | 28.73 | 32.67 | 31.57 | 0.99 | Oblate-spheroidal | Hexacolporate/ Tricolporate | 3.11 | 4.82 | 2.97 | obtuse | 2.05 | 2.97 | 8.97 | 6.86 | 6–7 | distended |
Dahlia pugana | 29.11 | 33.23 | 31.09 | 29.56 | 33.94 | 31.78 | 0.98 | Oblate-spheroidal | Tricolporate | 3.42 | 4.41 | 4.08 | obtuse | 2.68 | 2.23 | 6.22 | 6.35 | 6–7 | distended |
Dahlia rudis | 30.08 | 35.73 | 33.29 | 33.40 | 36.78 | 34.94 | 0.95 | Oblate-spheroidal | Hexacolporate/ Tricolporate | 3.06 | 4.19 | 2.50 | acute | 2.41 | 2.50 | 8.19 | 7.74 | 6–7 | narrower |
Dahlia rupicola | 28.20 | 35.37 | 31.16 | 26.92 | 32.40 | 30.08 | 1.04 | Prolate-spheroidal | Tricolporate | 1.71 | 3.36 | 2.76 | obtuse | 2.41 | 2.76 | 8.36 | 5.99 | 6–7 | distended |
Dahlia scapigera | 26.68 | 32.66 | 30.56 | 27.01 | 31.57 | 29.38 | 1.04 | Prolate-spheroidal | Tricolporate | 2.15 | 6.58 | 2.65 | acute | 2.68 | 2.65 | 7.90 | 6.09 | 4–5 | narrower |
Dahlia sorensenii | 28.87 | 34.80 | 31.90 | 30.73 | 36.42 | 33.90 | 0.94 | Oblate-spheroidal | Hexacolporate/ Tricolporate | 1.68 | 5.17 | 2.40 | obtuse | 1.73 | 2.40 | 9.07 | 6.12 | 4–5 | narrower |
Dahlia spectabilis | 27.71 | 34.07 | 30.33 | 25.20 | 32.12 | 30.11 | 1.01 | Prolate-spheroidal | Tricolporate | 2.46 | 4.72 | 2.05 | obtuse | 1.54 | 2.05 | 8.57 | 6.00 | 6–8 | distended |
Dahlia tenuicaulis | 28.54 | 32.84 | 31.03 | 31.58 | 35.37 | 33.01 | 0.94 | Oblate-spheroidal | Tricolporate | 2.82 | 4.19 | 4.94 | obtuse | 2.56 | 2.79 | 9.22 | 6.43 | 7 | distended |
Dahlia wixarika | 27.85 | 33.23 | 30.12 | 27.24 | 32.07 | 30.15 | 1.00 | Spheroidal | Tricolporate | 2.42 | 3.36 | 2.63 | obtuse | 2.95 | 2.63 | 7.44 | 6.01 | 7–9 | narrower |
Hidalgoa pentamera | 25.73 | 30.35 | 27.97 | 25.10 | 30.27 | 26.94 | 1.04 | Prolate-spheroidal | Tricolporate | 1.78 | 14.97 | 3.29 | acute | 2.06 | 9.98 | 5.47 | 6.09 | 4–5 | narrower |
Hidalgoa ternata | 28.01 | 34.07 | 30.36 | 26.45 | 32.08 | 29.63 | 1.02 | Prolate-spheroidal | Tricolporate | 1.71 | 14.55 | 3.34 | acute | 2.89 | 8.21 | 5.80 | 4.63 | 4 | narrower |
A matrix based on thirteen pollen characters was constructed. To estimate the quantitative variation within Dahlia and Hidalgoa, each character was measured and the average for each species was estimated. Qualitative characters were coded with the following states: number of apertures (tricolporate:0/ hexacolporate:1), colpus end (obtuse:0/ acute:1), base of spine (narrower:0/ distended:1) lalongate ora (absent:0/ present:1; present/absent:2) (Suppl. material
Palynological characters used in the multivariate analysis of Hidalgoa and Dahlia species. The contribution of every character for Axis 1 and Axis 2 is indicated (see Fig.
Character | Axis 1 | Axis 2 | ||
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1 | Pa | Polar axis (μm) | 1.63 | 23.53 |
2 | Et | Exine thickness (μm) | 6.59 | 2.30 |
3 | Cl | Colpus length (μm) | 25.18 | 1.19 |
4 | Cw | Colpus width (μm) | 8.88 | 10.75 |
5 | Ow | Os width (μm) | 22.82 | 1.34 |
6 | Ol | Os length(μm) | 3.75 | 11.48 |
7 | Sl | Spinae length (μm) | 7.98 | 10.97 |
8 | Swab | Spine width at base (μm) | 5.48 | 20.32 |
9 | Na | Number of apertures | 1.06 | 2.37 |
10 | Ns | Number of spines/100 μm2 | 4.49 | 11.70 |
11 | Ce | Colpus ends | 8.81 | 0.25 |
12 | Sb | Base of spine | 3.14 | 1.55 |
13 | Osl | Os lalongate | 0.20 | 2.23 |
Pollen grains from a total of 25 species belonging to Dahlia (23 species) and Hidalgoa (2 species) were analyzed. Table
Pollen grains of Dahlia and Hidalgoa observed with light microscopy (LM) A D. australis B D. barkerae C D. brevis D campanulata E D. coccinea F D. cordifolia G D. cuspidata H D. dissecta I D. imperialis J D. linearis K D. merckii L D. mollis M D. neglecta N D. parvibracteata O D. pugana P D. rudis Q D. rupicola R D. scapigera S D. sorensenii T D. spectabilis U D. rudis, pollen grain hexacolporate with three apertures on one hemisphere and three on the other hemisphere V H. ternata W H. pentamera. Scale bars: 10 μm.
Scanning Electron Microscope (SEM) images of Dahlia and Hidalgoa pollen grains A–C Hidalgoa ternata A equatorial view B detail of colpus C detail of spine D–F Dahlia australis D polar view E detail of colpus F detail of spine G–I Dahlia cuspidata G equatorial view H detail of colpus I detail of spine J–L Dahlia neglecta J equatorial view K detail of colpus L detail of spine M–O Dahlia coccinea M equatorial view N detail of colpus O detail of spine.
Scanning Electron Microscope (SEM) images of Dahlia and Hidalgoa pollen grains A, B Dahlia atropurpurea C Dahlia barkerae D, E Dahlia brevis F Dahlia dissecta H Dahlia imperialis I Dahlia linearis J Dahlia merckii K Dahlia scapigera L Dahlia tenuicaulis M Dahlia wixarika N–O Hidalgoa pentamera.
The majority of species analyzed in Dahlia are tricoloporate. However, two out of ten pollen grains are hexacolporate in D. cuspidata, D. dissecta, D. imperialis, D. merckii, D. parvibracteata, D. rudis and D. sorensenii, with three apertures on one hemisphere and three on the other hemisphere (Fig.
Pollen grains in the species of Hidalgoa analyzed are tricolporate and spheroidal-prolate (P/E = 1.02–1.04), radially symmetric. Pollen size is P = 25.7 (29.1) 34 μm, E = 25.1 (28.5) 32 μm (Fig.
Results of the PCA indicate that the first two components explain 46.04% of the observed variation (see Table
Principal Components Analysis graph showing contribution of the thirteen attributes to explain variation in pollen grains of the studied Dahlia and Hidalgoa species. Pa Polar axis, Et Exine thickness, Cl Colpus length, Cw Colpus width, Ol Os length, Ow Os width, Sl Spine length, Swab Spine width at base, Na Number of apertures, Ns Number of spines/100 μm2, Ce Colpus ends, Sb Base of spine, Osl Os lalongate.
The pollen grains of the 25 species of Dahlia and Hidalgoa we studied share the pollen type common to tribe Coreopsideae: more or less spheroidal, round in both views, tricolporate, ora lalongate, tectum microperforate, echinate, spines irregularly distributed, conical to long-pointed and smooth or distended bases with perforations (
Comparison of Dahlia and Hidalgoa pollen grains A box plot of Polar diameter B os length/width C colpus length/width D spine length/width at base. 1 Dahlia atropurpurea. 2 Dahlia australis. 3 Dahlia barkerae. 4 Dahlia brevis. 5 Dahlia campanulata. 6 Dahlia coccinea. 7 Dahlia cordifolia. 8 Dahlia cuspidata. 9 Dahlia dissecta. 10 Dahlia imperialis. 11 Dahlia linearis. 12 Dahlia merckii. 13 Dahlia mollis. 14 Dahlia neglecta. 15 Dahlia parvibracteata. 16 Dahlia pugana. 17 Dahlia rudis. 18 Dahlia rupicola. 19 Dahlia scapigera. 20 Dahlia sorensenii. 21 Dahlia spectabilis. 22 Dahlia tenuicaulis. 23 Dahlia wixarika. 24 Hidalgoa pentamera. 25 Hidalgoa ternata.
Apertures are the most variable attribute between Dahlia and Hidalgoa, but not within the genera. Pollen in Hidalgoa is always tricolporate, while in pollen grains of Dahlia, the aperture varies from tricolporate to hexacolporate. Hexacolporate species observed here were: D. cuspidata, D. dissecta, D. imperialis, D. merckii, D. parvibracteata, D. rudis and D. sorensenii.
The os and colpus displayed more variation in Dahlia than in Hidalgoa. In Hidalgoa the os is lalongate, the widest is up to 13 μm width, and the longest colpus is approximately 17 μm, with apices always acute. These traits of Hidalgoa are similar to those observed in Bidens (
Spines are variable between Dahlia and Hidalgoa. In Hidalgoa they are conical and smaller (4.08 to 6.77 μm) while in Dahlia they are deltate and larger (4.29 to 12.26 μm), with exception of D. linearis (smaller). Spines in Dahlia varied more in shape and size. They are commonly triangular or deltate with a broadened base (distended base), as described by
Multivariate analyses did not reveal a clear clustering among species of Dahlia according to the sections proposed by
The most recent phylogeny that included Dahlia and Hidalgoa (
The palynological descriptions for Hidalgoa presented here are the first, and despite the similarities in its floral morphology to that of Dahlia, its pollen is remarkably different, mostly in colpus length and shape of their spines. Hidalgoa has pollen grains with large colpi and small, conical spines. In addition, the length of the lalongate ora differ. Hexacolporate grains with a distended base, were found in a number of Dahlia species but have not been identified in Hidalgoa. Likewise, morphological characters such as pistillate fertile ray florets, cypselae with two apical lateral cusps and twisting petioles in Hidalgoa contrast with the ray florets, which can be fertile, pistillate or sterile, cypselae with pappus absent or present with 2(5) small teeth or of two weak filiform, caducous bristles of Dahlia; characters that have been utilized to tell these two genera apart. The results obtained in this palynological study support the idea that pollen morphology is useful for delimitation at the generic level in the Dahlia clade. These differentiating attributes in pollen morphology in the species of Dahlia and Hidalgoa indicate that they should be recognized as separate genera. However, as indicated above, additional anatomical and molecular characters are needed to make the taxonomic decision and help us understand evolution in the genera, and their relationship to other genera in Coreopsideae.
We thank Tadesse Mesfin, Arturo Castro-Castro and an anonymous reviewer for comments and suggestions that greatly improved this manuscript. We thank the curators of the
Tables S1, S2
Data type: Tables (docx. file)
Explanation note: Table S1. Dahlia diversity. Sections proposed by Sorensen (1969). Table S2. Data matrix showing the values found for the 13 characters (columns) in the 25 species (rows) of Hidalgoa and Dahlia included in this study. (Characters designated according to Table