Dahlia calzadana Villaseñor & Redonda-Mart., 2018

Villaseñor, José Luis & Redonda-Martínez, Rosario, 2018, A new species of Dahlia (Asteraceae, Coreopsideae) from the state of Oaxaca, Mexico, Phytotaxa 362 (2), pp. 239-243 : 240-242

Dahlia calzadana Villaseñor & Redonda-Mart. , sp. nov. ( Fig. 1)

Type: — México. Oaxaca: Dto. Cuicatlán, Mpio. San Juan Bautista Cuicatlán, 3 km antes del poblado San Juan Coyula, sobre la carretera vecinal de terracería de Quiotepec a San Juan Coyula, elev. 1250 m, 17°55’24.74” N, 96°56’15.6” O, 20 julio 2003, J. I. Calzada 23910 (holotype: MEXU!; isotypes: IEB!, TEX!, XAL!) .

Description:—Suffrutices 0.4–0.6 m tall. Stems terete, succulent, striate, glabrous. Leaves simple, opposite, petioles (1.1–2.8–) 6.1–9.5 cm long; blades (2.2–) 10.3–12 cm long, (1.4–) 5–9.5 cm wide; ovate, margin crenate or dentate, adaxial and abaxial surfaces glabrous, young leaves scarcely pilose below. Heads heterogamous, solitary or in clusters of 2–3, terminals, peduncles (5.3–) 9.2–12.5 cm long, glabrous; involucre campanulate to hemispheric, 2-seriate, glabrous, (1–)1.2–1.8(–2.4) cm long, (1.5–)1.8–2.5(–3.2) cm wide; phyllaries 8–10, the outer series green, shorter than the inner series 4.2–5 mm long; the internal series brown, 1.2–1.8(–2.4) mm long, margins scarious. Ray florets 8–10, neutral, corollae whitish with pink tones, flattened, tube (2.8–) 3.5–4.4 mm long, glandular, laminae (1.3–) 2.6–3.2 cm long, papillose; disc florets 55–60, hermaphrodite, yellow, corollae tubular, pentamerous, 6.5–7.2(–10.2) mm long, tube 2.2–2.6 mm long, lobules 4.3–6.6(–8) mm long, pilose; style 5.5–5.8 mm long, branches flattened, acute and pilose, 3.4–3.6 mm long; anthers 5.1–5.3 mm long, apical appendices lanceolate–apiculate, base sagittate; cypselae ellipsoid, 5–6-ribbed, 9.8–10.2 mm long, puberulent to sparsely pilose; pappus absent.

The species is similar to Dahlia brevis , D. cordifolia and D. purpusii in sharing simple leaves, but differs from them in its habit (suffruticose vs. herbaceous) and its whitish with pink tones (vs purplish or lavender) radiate florets.

Distribution, habitat and phenology:— Dahlia calzadana is currently known from the type collection and one additional record, collected in seasonal dry tropical forest, at its ecotony with Quercus forest. It grows on dark, rocky soil with limestone outcrops. The two known localities are placed inside the Valle de Tehuacán-Cuicatlán Biosphere Reserve. Flowers and fruits from May to July.

Etymology:—The specific epithet honors Ismael Calzada, an enthusiastic and prolific plant collector who for many years has explored the Biosphere Reserve where this species was found.

Conservation Status:—According to IUCN (2004), Dahlia calzadana must be considered Vulnerable B2a, largely due to its restricted distribution (known only from two localities) in a well studied region with a conservation status notably the Valle de Tehuacán-Cuicatlán Biosphere Reserve.

Additional specimen examined:— MEXICO. Oaxaca: Loma de Buena Vista, 10 km al E de Quiotepec, elev. 1300 m, 17°55’26” N, 96°56’57.5” O, 5 mayo 1990, A. Salinas et al. 5421 (MEXU!).

Discussion:—The new species is included in Dahlia section Dahlia because, like the other known species of the section, it has reflexed outer involucral bracts and leaves simple and opposite. However, it differs from the other species of the section because of the woody basal part of the stem, a character only observed in this new taxon.

Dahlia calzadana may be related to D. brevis P.D. Sørensen (1969: 368) , D. cordifolia (Sessé & Moc.) McVaugh (2000: 148) , and D. purpusii Brandegee (1914: 76) , by sharing simple leaves; however, only D. calzadana develops a suffruticose habit. On the other hand, D. calzadana may be confused by its habit with D. scapigeroides Sherff (1947: 145) and D. sublignosa (P.D. Sørensen) Saar & P.D. Sørensen (2005: 545) , although the two latter species have pinnate leaves with elliptic or lanceolate segments, lower number of ray florets (≤ 8 vs. 8–10) with purple or pink colorations. By contrast, D. calzadana produces whitish ray florets with pink tones; in addition, this is the only species of the section growing further south (Oaxaca); the other members of the section are mostly found in central and northeastern Mexico (Guanajuato, Hidalgo, Queretaro and northwards).