Dahlia mixtecana Reyes, Islas & Art. Castro, 2019
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publication ID |
https://doi.org/ 10.11646/phytotaxa.394.3.2 |
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persistent identifier |
https://treatment.plazi.org/id/2C6A87B1-FFEB-FF86-FF21-F902ABCD6CE6 |
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treatment provided by |
Felipe |
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scientific name |
Dahlia mixtecana Reyes, Islas & Art. Castro |
| status |
sp. nov. |
Dahlia mixtecana Reyes, Islas & Art. Castro View in CoL sp. nov. ( Figures 3 View FIGURE 3 and 4 View FIGURE 4 )
Due to a particular combination of characters, Dahlia mixtecana is related to Dahlia sect. Dahlia and Dahlia sect. Entemophyllon SØrensen (1969: 340), but is distinguished from any species of these sections by bipinnate leaves, solid petioles, linear lanceolate and alternate or opposite pinnular segments, and yellow ray florets; in addition, it is characterized by its habitat preferences and restricted distribution.
Type: — MEXICO. Oaxaca: Municipio de San Bartolo Yucuañe, Distrito de Tlaxiaco, Cerro Shicava , 0.5 km S de El Llano , rumbo a Teita y a 5 km S de la cabecera municipal de San Bartolo Yucuañe, 1788 m, 28 August 2011 (fl, fr), J. Reyes & M. A. Islas-Luna JE-7272 (holotype MEXU!; isotypes CIIDIR!, IBUG!) .
Herbaceous 0.9–1.2 m tall, perennial from tuberous rootstock, 15–20 × 5–6 cm in living individuals. Stems erect, solitary or cespitose, solid throughout its length, cylindrical, dark reddish, reddish brown, to bright cherry, smooth to puberulent in the upper portion of the nodes and the base of the petioles, internodes 2–4 cm, solid, glabrate, without evident septum in the nodes, but in some cases slightly light green. Leaves bipinnate, ovate to elliptic in general outline, 12–18 × 10–12.5 cm; petioles (3–)6.5–7 × 0.2–0.4 cm, evidently connate-perfoliate, canaliculated, solid, reddish; stipels ovate to rhomboid, 5.8–7 × 1.5–3 cm, present from the first to the second pair of leaflets, sometimes solitary, pinnate lobulate; pinnae 5, opposite on the rachis, ovate to lanceolate, 6.5–8.5 × 5–8(–11) cm, terminal pinnae pinnatisect, lanceolate to ovate, 5–7 × 4.5–6 cm, all with apex acuminate, base obtuse, margins ciliate, dull green, glabrate, petiolules 1–1.5 cm long; pinnules alternate or opposite on the rachilla, linear-lanceolate, 3.5–6.5 × 0.5–2.5 cm, sessile to decurrent, all with mucronulate apex, margins entire, glabrous, bicolored, dark green on the upper surface, whitish green on the underside, with notoriously dark venation. Synflorescence corymbiform, heads 3–6; peduncles 35–45 cm long, solid, glabrous, light green to reddish, central peduncle 9–14 × 0.2 cm, lateral peduncles 7–14 × 0.1–0.12 cm. Heads 6–7 cm wide across the extended rays, 2.5–3.7 cm long. Involucre 1–1.3 × 0.8–1 cm, cup-shaped. Involucral bracts biseriate; outer series 5, dark green on the adaxial surface and light green on the abaxial side, glabrous, reflexed at anthesis, lanceolate, 1–1.3 × 0.25–0.5 cm, acute or rounded apex, with 5–8 dark reddish resiniferous ducts, coriaceous; inner series 8, translucent yellow to reddish, glabrous, lanceolate to ovate, 1.1–1.3 × 0.3–0.4 cm, apex acute, with 20–22 light reddish resiniferous ducts. Receptacle plane, paleaceous, 5–9 mm diameter, tomentulose. Paleae translucent yellow to reddish, bright when dehydrated, 6–7 × 2.5–3 mm, persistent and resembling the inner involucral bracts. Ray florets 8, uniseriate, sterile, yellow, limb lanceolate to elliptic, 1.6–2.2 × 1.2–1.5 cm, 2–4 ribbed outside, ribs glabrescent, apices obtuse, entire to trilobulate, tube 3.4–3.7 × 0.9–1.5 mm, glabrescent. Disk florets 27–33, light yellow to whitish, funnel-shaped, 7–10 mm long; corolla tube 5–6 × 1–1.4 mm, glabrous; throat 1–1.5 mm wide; lobes 5, 0.5–0.8 mm long, erect, triangular. Anthers 5–5.5 mm long, light brown, apical appendages triangular, short sagittate at the base; pollen yellow. Style ca. 8 mm long; stigma lobes ca. de 2.5 mm long, yellow, acute, penicillate, long papillate beneath and along the margins. Cypsela clavate, 7–10 × 1.5–2 mm, furrowed, brownish, glabrate, scabrous on the rounded angles, attenuate, carpopodium annular, pappus absent.
Distribution, habitat and phenology:— Dahlia mixtecana is only known from a mountain known locally as Shicava or Yacava, in San Bartololo Yucuañe, district of Tlaxiaco, Mixteca Alta, Oaxaca ( Figure 2 View FIGURE 2 ). It grows on limestone soil on steep slopes in a xerophilous scrub dominated by Neobuxbaumia aff. tetetzo (Weber ex Schumann 1899: 175) Backeberg (1938: 6) , and remains of oak forest of Quercus acutifolia Née (1801: 267) dominated by Agave sp. , Begonia sp. , Brahea dulcis ( Kunth 1815: 300) Martius (1838: 244) , Dasylirion acrotrichum ( Schiede 1829: 230) Zuccarini (1840: 228) , Hechtia sp. , Rhus oaxacana Loesener (1906: 834) and Selaginella sp. ( Figure 4 View FIGURE 4 ). Dahlia mixtecana blooms from late August to late September and mature cypselae can be collected in October.
Conservation assessment: — Dahlia mixtecana is represented by one collection from one population ( Figure 2 View FIGURE 2 ). During the field work for the collection of materials, it was not possible to count the number of individuals in the population. Based on minimum convex polygon and cells of 2 × 2 km and using GeoCAT program ( Bachman et al. 2011), we calculated that the Extent of Occurrence (EOO) was 0 km 2, and 4 km 2 for the Area of Occupancy (AOO). Following the IUCN (2012) criteria, the results of this study allowed us to determine the Extent of Occurrence and the Area of occupancy estimated to be less than 100 km 2 and that the species occurs at only one known locations, so that a preliminary category of Critically Endangered is proposed (CR/B1a).
Etymology:— The specific epithet refers to the Mixteca culture from Oaxaca, Mexico.
Additional material examined (paratypes):— MEXICO. Oaxaca: Municipio de San Bartolo Yucuañe, Distrito de Tlaxiaco, Cerro Shicava, 0.5 km S de El Llano, rumbo a Teita y a 5 km S de la cabecera municipal de San Bartolo Yucuañe, 1788 m, 21 July 2011 (sterile), J. Reyes, M.A. Islas-Luna & O. González-Zorzano 7142 (cultivated in IBUNAM Botanical Garden).
Taxonomic relationships:— Based on the presence of solid petioles, bipinnate leaves and pinnules alternate or opposite on the rachilla, Dahlia mixtecana could be placed in Dahlia sect. Entemophyllon . According to Sørensen (1969), all the species in Dahlia sect. Entemophyllon produce many stems arising from a common tuberously thickened rootstock, a marked character that contrasts with the usual single-stemmed habit of all other species in the genus. Nevertheless, multiple stems are also present in species not included in Dahlia sect. Entemophyllon , for example: D. apiculata ( Sherff 1947: 145) Sørensen (1969: 356) , D. coccinea Cavanilles (1794: 33) and D. rudis Sørensen (1969: 369) . These features together with the segmentation of the leaves are the most remarkable characteristics in Dahlia sect. Entemophyllon that embraces: D. congestifolia Sørensen (1987: 198) from the state of Hidalgo; D. dissecta Watson (1891: 141) from Hidalgo, Querétaro and San Luis Potosí; D. foeniculifolia Sherff (1951: 71) from Nuevo León and Tamaulipas; D. linearis Sherff (1930: 364) from Guanajuato and Querétaro; D. rupicola Sørensen (1969: 346) from Durango and Zacatecas; D. scapigeroides Sherff (1947: 145) from Guanajuato, Hidalgo, Querétaro, San Luis Potosí; and D. sublignosa ( Sørensen 1969: 351) Saar & Sørensen (2006: 545) from Nuevo León, San Luis Potosí and Tamaulipas ( Reyes-Santiago et al. 2018, Carrasco-Ortiz et al. 2019).
Most of the above mentioned species have small woody stems that persist in the year and lilac ligules, except Dahlia dissecta which develops annual stems and white to lilac ligules. However, D. mixtecana can be distinguished by yellow ray florets and by its geographical distribution, which represents the southern limit for Dahlia sect. Entemophyllon ( Figure 2 View FIGURE 2 ).
Dahlia mixtecana could be also associated to Dahlia sect. Dahlia , based on the variable position of the pinnular segments, solid petiole, reflexed outer involucral bracts and yellow rays. Under this assumption, due to the yellow color of the ray florets D. mixtecana could only relate to D. coccinea , D. mollis Sørensen (1969: 373) and D. tenuis Robinson & Greenman (1897: 48) . However, D. mixtecana is different from D. coccinea by ray florets color (yellow vs. yellow, orange, orange-red, scarlet, bright red, dark red or blackish red), leaves (bipinnate and alternate vs. simple to tripinnate and alternate or whorled), pinnular segments (linear-lanceolate and opposite or alternate vs. lanceolate to ovate and opposite), outer involucral bracts (lanceolate vs. ovate, obovate or spatulate), and amount of disk florets (27–33 vs. 50–160). Meanwhile, D. mixtecana differs from D. mollis by their bipinnate leaves, leaves and stems smooth to puberulent, by the development of stipels from the first to the second pair of leaflets and the yellow ray florets (vs. pinnate leaves, leaves and stems densely soft pubescent, stipels absent and mostly lilac but sometimes pale yellow ray florets). In the last case, D. mixtecana can be differentiated from D. tenuis more easily by its height (0.9–1.2 m vs. 0.25–0.6 m), pubescence of stems (smooth to puberulent vs. conspicuously pubescent), segmentation of leaves (bipinnate vs. pinnate), length of petioles [(3–) 6.5–7 cm vs. 0.8–4.5 cm], heads per plant or on each main branch (3–6 vs. 1–4) and length of disc florets (7–10 mm vs. 3.5–4.5 mm).
Some characteristics could place Dahlia mixtecana in Dahlia sect. Entemophyllon , but other traits would be unique to the section, although found elsewhere in the genus (e.g., reflexed outer involucral bracts and yellow rays florets in Dahlia sect. Dahlia ). Species in Dahlia sect. Entemophyllon have a unique chromosome number (x = 17) and two molecular studies have provided a distinct molecular profile for species in the clade ( Gatt et al. 2000, Saar et al. 2003). Based on the current evidence available and the current infrageneric classification of the genus, it does not appear possible to assign D. mixtecana with confidence to any phylogenetic clade or taxonomic section. The overlap of characters in Dahlia species from different sections has been observed by other authors and suggests that the current infrageneric arrangement is not natural and requires revision ( Castro-Castro et al. 2015, Villaseñor & Redonda-Martínez 2018). We recommend that the phylogenetic position and the chromosomal number of D. mixtecana be analyzed in future studies.
Finally, a key for the identification of Dahlia species growing in Oaxaca, following the biogeographical analyses of Carrasco-Ortiz et al. (2019), and based on Sørensen (1969), Hansen (2007) and Reyes-Santiago et al. (2018) is presented below. Due to the aforementioned problems, D. mixtecana is placed optionally under two infrageneric groups.
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