Magnolia mixteca A.Vázquez & Domínguez-Yescas, 2021

Vázquez-García, J. Antonio, Yescas, Reyna Domínguez, Luna-Vega, Isolda, Rodríguez-Ramírez, Ernesto C. & Rodríguez-Pérez, Ciro, 2021, Corncob flower, Magnolia mixteca (M. sect. Macrophylla, Magnoliaceae) a new species endemic to the Alto Balsas Basin (Baja Mixteca), in the Pacific slopes of Oaxaca, Mexico, Phytotaxa 522 (3), pp. 200-210 : 202-208

Magnolia mixteca A.Vázquez & Domínguez-Yescas , spec. nov. ( Figs 1–5 )

Type:— MEXICO. Oaxaca: Mpio. Santiago Juxtlahuaca, 5 km del poblado El Manzanal [San Lorenzo Manzanal], carretera a Infiernillo, bosque de pino-encino, suelo negro rocoso, 1835 m, 17.13 ° N, 98.04 ° W, 14 Dec 1995 (fr & fl), Calzada 20619 (holotype: MEXU!) .

Magnolia mixteca is morphologically similar to the geographically distant M. nuevoleonensis in having broadly ovoid, broadly ellipsoid to subglobose fruits. However, it differs from M. nuevoleonensis in having larger flowers, 25–30 (vs. 20–24 cm in diam.); longer petals, 14.2–15.2 (vs. 10.0–11.0 cm); petal blotch when present broad and yellow (vs. narrow and dull purple); stamens 349–409, yellow (vs. 200–220, white); ovary colour tan (vs. white); and more numerous carpels 58–64 (vs. 30–42).

Deciduous trees, 8–18 m, 10–70 cm in diameter; trunk erect, conical, crown sparse, top branched; bark slightly scaly, fissured longitudinally, and lenticels and leaf scars sparse. Petioles 4.5–5.6 cm long, 0.5–1.0 cm in diameter; stipules united 3/4 of the length of the petiole, oblong-lanceolate, with acute apex, densely scattered on the abaxial side, sericeous, glabrous adaxially. Leaves obovate, acute at the apex, auriculate or cordate at the base, leaf blades 24.0–37.0 × 22.0– 31.5 cm, adaxially glabrous and green, abaxially white-glaucous (due to their sericeous epicuticular surface) and pubescent in the veins, midvein 3.8–4.0 mm in diameter at the base. Bracts 1, spathaceous, 8.0–8.5 × 5.7–6.0 cm, ovate-oblong, abruptly truncate near the base, deeply cochleate, abaxially glabrous, with 10 secondary veins, yellowish and turning rusty brown. Pedicel (distal internode) 1.3–1.4 long, 1.5–1.6 cm diameter, glabrescent and usually glaucous towards the apex, the adjacent internode glabrescent, 3.0–3.2 long, 1.3–1.5 cm diameter. Flowers 25.0–30.0 cm, white when young, creamy white when ripe, with a broad yellow blotch, 3.0–3.2 × 3.2–3.5 cm, at the base of petals over the area of sticky secretions, starting 2–4 cm away from the base, the distal border of the blotch lacerate. Sepals 3, 9.2–13.7 × 4.1–5.1 cm, ovate-oblong, truncate basally, acute apically, green when young, turning yellowish green with distinct veins, glabrous and often glaucous. Outer petals 3, 14.2–15.2 × 4.5–5.6 cm, ovate oblong-elliptical, acute apex, abruptly, shortly clawed basally, white end turning creamy white, glabrous. Inner petals 3, 9.3–14.6 × 3.8–5.0 cm, oblong-elliptic, acute to obtuse at the apex, attenuated at the base, claws twice as long as the outer petals, white end turning creamy white, glabrous. Floral axis 4.8–5.2 cm long, androphore 1.4–1.6 × 1.0– 1.5 cm, yellow. Stamens 349–409, linear, 1.0–1.3 × 0.2–0.3 cm, yellow to white-yellowish, round to obtuse apically, truncate basally. Gynoecium 3.3–3.5 long, 2.3–2.5 cm in diameter; carpels 58–64, 1.5–1.7 cm long, ovaries 0.8–0.9 × 0.4–0.5 cm, obovate, channeled at the axis, tan-sand colored, pubescent. Styles 0.7–0.8 × 0.2–0.3 cm, linear, flat, incurved, white, glabrous, creamy white to beige, turning dark brown to black at the tip and the inner apical borders ( Fig. 3 ). Fruit stalk 2.3–2.6 cm long, 0.9–1.1 cm in diameter, glabrous; poly-follicles 6.5–9.7 cm long, 5.4–7.5 cm diameter, broadly ellipsoid to subglobose; follicles 1.0–2.0 × 1.2-1.5 cm, puberulous. Seeds 1–2 per carpel, 0.8–0.9 × 0.6–0.7 cm, ovoid to oblongoid or sub pyramidal, with obtuse base and apex, pink to red sarcotesta.

Distribution and ecology:— Magnolia mixteca inhabits the Alto Balsas Basin in Baja Mixteca, Oaxaca, at 1800– 2300 m within the Sierra Madre del Sur biogeographic province. The population size is undetermined and occurs in tropical montane cloud forest remnants of the Juxtlahuaca District. Expeditions to locate additional populations of this species in the Juxtlahuaca District are necessary.

Phenology:— Flowering April–May, fewer flower buds are still present in late May; fruiting September–October; roughly a quarter of leaves remain in May.

Ethnobotany:— Locally known as ita ndixin (Mixtec), “corncob flower” and named for the native language of the area. Also known as in Spanish as flor de queso (cheese flower). The showy and fragrant flowers are sold locally in the Abastos market of La Reforma de Juquila. Locals use the flowers to relieve pain and treat heart deficiencies.

Conservation status:— We assessed M. mixteca as endangered (E) because this species met the criteria [B1, B(a) and (b)iii] of IUCN (2019). The distribution area of Magnolia mixteca is highly restricted, EOO <5000 km 2, and AOO <500 km 2. It has only been found in the municipality of Santiago Juxtlahuaca, Oaxaca. The population density is not yet determined. The label of of the type material collected in 1995 indicates that the species had a “regular abundance”. Recent explorations during 2021 at a different location allowed us to find only a single tree and a second one in a disturbed area. Locals know this tree, but they do not have any interest in its propagation or conservation. We did not observe regeneration, but records from the Naturalista website (https://www.inaturalist.org/photos/18523679) uploaded by Hermelinda Santos show photographs of two juveniles in the forest of Río Santiago Copala, Juxtlahuaca. Birds and small mammals eat the seeds. We suggest including this magnolia species in the Mexican NOM-059 (SEMARNAT 2010) and the IUCN Red List of Magnoliaceae ( Rivers et al. 2016) as an endangered species due to its restricted distribution and obvious threats to its habitat.

Notes:— Magnolia section Macrophylla now includes nine species, two in the United States and seven in México. Magnolia mixteca differs in latitude from M. nuevoleonensis : 17 ° 07’–17 ° 17’ vs. 25 ° 11’–25 ° 39’; elevation: 1500–1700 vs. 1800–2300 m; mean annual rainfall: 1600 –2,177.1 vs. 864.5 mm; hydrographic regions: Alto Balsas Basin vs. San Juan-Río Grande watershed and biogeographic provinces: Sierra Madre del Sur vs. Sierra Madre Oriental ( Morrone et al. 2017). The emergence of the TVB and the climatic changes in the Miocene played a key role as vicariant events causing isolation between the northern and southern populations ( Ibarra-Martínez 2020). The interruption of gene flow and selective climatic pressures allowed diversification, resulting in a similar allopatric latitudinal radiation to the reported in the M. sect. Magnolia in western Mexico ( Vázquez-García et al. 2021), the last one under different selective pressures. It is not known if M. mixteca is more similar genetically to the morphologically most similar but geographically distant species, M. nuevoleonensis , or to its geographically nearest species, M. dealbata .

Some herbarium specimens of M. mixteca from MEXU were misidentified as yoloxóchitl, Talauma mexicana ( Candolle 1817: 451) Don (1831: 85) [ Magnolia mexicana DC. ], but the latter belongs to M. section Talauma , an evergreen tropical tree with woody apocarpous fruits and circumscissile dehiscence ( Vázquez-García et al. 2015).

Additional Specimens examined: — MEXICO. Oaxaca: Juxtlahuaca District., Coicoyán municipality, cultivated in town on agricultural parcel, 2000 m, 17 16,N, 98 17 W, 25 May 1989 (fl) Avila 317 ( MEXU) ; Municipality of Santiago Juxtlahuaca, trail to Guadalupe Luchio El Alto, 1/ 2 km south of San Miguel Cueva , 2290 m, 17°14’12.22” N, 98° 2’49.20” W, 15 May 2021 (fl), Domínguez-Yescas & Rodríguez - Perez 79 ( IBUG, MEXU) ; 4 km, straight-line, SW of San Miguel Cueva, Piedra Espejo, San Lorenzo del Manzanal , toward Arroyo Infiernillo , 2080 m, 17°12’54.58” N, 98° 4’4.93” W, 15 May 2021 (st), Domínguez-Yescas & Rodríguez - Perez 80 (Photograph-IBUG); La Reforma de Juqiula , Mercado de Abastos , 15 Apr 2021 (fl), Martin M 018 ( MEXU) .

Figures

FIGURE 1. Distribution of Magnolia sect. Macrophylla in the Mexican biogeographical provinces (Morrone 2017). The new species, M. mixteca, has the southernmost location in the only watershed draining into the Pacific Ocean.

FIGURE 2. Magnolia mixteca. A. Leaf, adaxial side, with large stipules. B. Flower bud. C. “Corncob” flower bud. D. Spathaceous bract. E. Leaf, abaxial surface. (Photos Ciro Rodríguez Pérez.)

FIGURE 3. Magnolia mixteca. Flowering branch in male phase. (Photo Ciro Rodríguez Pérez.)

FIGURE 4. Magnolia mixteca. A. Flowering branch showing the basal yellowish petal spots. B.Androecium (basal) showing the stamens and gynoecium (apical) in female phase, before pollination, showing the styles. C. Gynoecium in male phase after pollination, without stamens, showing the staminal axis and ovary of basal carpels. (Photos Reyna Domínguez Yescas and Ciro Rodríguez Pérez.)

FIGURE 5. Magnolia mixteca. A. Petals and sepals, one day after the male phase. B. Fruit of the previous year with some seeds trapped. C. Fruit variability, empty and collected from the ground. (Photos Reyna Domínguez Yescas and Ciro Rodríguez Pérez.)