Populus luzae A.Vázquez, Muñiz-Castro & Padilla-Lepe, 2017

Vázquez-García, J. Antonio, Muñiz-Castro, Miguel Ángel, Padilla-Lepe, Jesús, Ávila, María Guadalupe Pulido, Hernández, Gregorio Nieves & González, Rosa Elena Martínez, 2017, Populus luzae (Salicaceae), a new species of white poplar endemic to the western Transmexican Volcanic Belt, in Zapopan, Jalisco, Mexico, Phytotaxa 328 (3), pp. 243-256 : 245-252

Populus luzae A.Vázquez, Muñiz-Castro & Padilla-Lepe sp. nov. ( Figs. 1–6 , 8 ).

Diagnosis:— Populus luzae A.Vázquez, Muñiz-Castro & Padilla-Lepe is morphologically close to P. guzmanantlensis ( Figs. 7 A–D ), but it differs from the latter in having smaller habit, producing suckers, narrower twigs and petioles; leaf blades widely ovate to ovate-deltoid, chartaceous rather than ovate to suborbicular, coriaceous, with adaxially less depressed veins; male bracteoles thrice smaller, ovate, with entire margin; female bracteoles twice longer, sparsely denticulate but unlobed; smaller number of pistillate flowers; capsules pubescent; mature male inflorescence twice longer, and infrutescence lax and longer.

Type:— MEXICO. Jalisco: Zapopan, Arroyo La Virgen, 1.15 km SW from Rancho San Nicolás , 9 km WNW from Santa Lucía , along a stream with relict cloud forest elements, 20 ° 48'53.22"N, 103 ° 34'51.30"W, 1425 m, 30 November 2012 (young fruit), Miguel A. Muñiz-Castro, Jesús Padilla-Lepe y Ana T. Nuño-Rubio 1150 (holotype IBUG!; isotypes IEB!, MEXU!, MO!, ZEA!,) .

Description: — Trees 15.0–20.0 m tall, trunk 0.3–1.5 m dbh; first branches from 2.0 to 3.0 m height, in any direction, rarely straight; clones spreading by means of root-borne sucker shoots (soboliferous); bark smooth and grayish at sapling stage, soon becoming deeply furrowed and occasionally tessellated; twigs lenticellate, slender, 2.0–4.0 mm thick, glabrous except the young green twigs puberulent to pubescent. Petioles (3.7–)4.5–6.0 cm long, occasionally shorter in young and shaded shoots, abaxially flattened at the base, 1.5 × 1.2 mm, adaxially convex, basically cylindrical halfway its length, barely compressed laterally, (1.2 × 1.0 mm) at the blade union, glabrous to pubescent. Leaf blades (9.5–)10.5–15.0(–16.0) × (7.8–)8.8–13.4(–14.2) cm, widely ovate to ovate-deltoid; base obtuse to rounded to subcordate; apex rounded to acute to shortly apiculate; margins crenate-dentate, 19–20 teeth per side, each topped by a dark gland; adaxial leaf surface glabrous, with slightly depressed veins; abaxial leaf surface puberulent, tertiary veins not very prominent. Male inflorescence ament, (25.0–)45.0–65.0(–72.0) × 6.0–8.0(–9.5) mm, cylindrical, pendulous and curved, with densely arranged flowers, rachis 0.7–0.8(–1.0) mm thick, white to creamy, brown when it dries, sparsely ciliate; bracteoles ovate 0.7–1.0 mm long, reddish brown, scarcely ciliated, margin entire, ciliate. Staminate flowers (50–)55–77(–85), pedicellate, 1.8–2.7 mm long; pedicels 0.3–0.5 mm long; floral disc meniscoid, shallow cup, shaped to patelliform, oblique, 1.0– 1.2 mm diam., creamy, when it dries: brown and yellowish; stamens 9–13, free, filaments glabrous 1.2–1.8 mm long; anthers basifix and oblong, 0.9–1.2 mm long, pale yellow. Female inflorescence ament, 50.0–60.0(–80.0) × 3.5–4.5 mm, cylindrical, lax, rachis (0.6–)0.7–0.9(–1.2) mm thick, creamy to greenish-yellow color, brown when it dries, sparsely ciliate; scales of axillar buds 6–7, 3.5–4.0 × 2.5–3.0 mm, brown reddish, glabrescent to pubescent; pedicels (0.1–) 0.2–0.3 mm long; bracteoles 2.6–3.2 × 1.2–1.3 mm, narrowly ovate to elliptic to broadly spathulate, margin sparsely denticulate to entire, none lobed, ciliate, caducous, greenish-yellow at anthesis, brown-reddish when they dry; pistillate flowers (35–)57–70(–77), ovate acuminate to conic; floral disc cuplike, oblique, scarcely ciliated; ovary pubescent to glabrescent; styles 2, each branched into curved stigmas. Infrutescences lax 50.0–81.0 × 3.5–6.0 mm; capsules bivalved, 2.0–2.5 × 1.3–1.6 mm (closed), pubescent, opening at the tip. Seeds 4–6 per capsule, 0.2 × 0.1 mm, ovoid, reddish brown.

Distribution, habitat, and phytogeography: —Apparently, Populus luzae is endemic to central Jalisco, in the Zapopan municipality ( Fig. 8 ), at 1425–1430 m elev., along only two streams at the northern and eastern edges of the “Mesa de Nextipac” plateau, respectively, in gallery forest ecotones with relict cloud forest elements such as Magnolia pugana , Persea liebmannii Mez (1889: 166) , Fraxinus uhdei Wenz. (1883: 182) Lingelsh. (1907: 221) , Prunus ferruginea Steud. (1841: 403) , and Clethra hartwegii Britton (1914: 6) ; and tropical moist forest elements such as Salix bonplandiana Kunth (1817: 24) , Lysiloma acapulcense Kunth (1821: 78) Benth. (1844: 83) , Platymiscium trifoliolatum Benth. (1860: 82) , Ficus petiolaris Kunth (1817: 49) , Oreopanax peltatus Linden (1859: 368) and Toxicodendron radicans L. (1753a: 266) Kuntze (1891: 153); the forest understory including Osmunda regalis L. (1753b: 1065), Psilotum complanatum Sw. (1801: 110) , Piper hispidum Sw. (1788: 15) , Chusquea circinata Soderstr. & C.E.Calderón (1978: 156) , Rhus trilobata Nutt. (1838: 219) and Verbesina fastigiata B.L.Rob. & Greenm. (1899: 558) . Outside the ravine, the western slopes are heavily disturbed and dominated by Pinus oocarpa Schiede ex Schltdl. (1838: 491) and Vachellia farnesiana L. (1753a: 521) Wight & Arn. (1834: 272), while the eastern slopes are less disturbed and dominated by Quercus resinosa Liebm. (1854: 182) . The cloud forest relicts most likely migrated from older refugia at the Sierra Madre Occidental mountain range to the more recent (late Miocene–Pliocene) Neovolcanic Plateaus supergroup ( Rodríguez-Castañeda & Rodríguez-Torres 1992), where they possibly survived Pleistocene climatic fluctuations in protected ravines with perennial streams. The extensive natural and artificial hybridization reported for the genus Populus in China and North America ( Shang et al. 2016, Eckenwalder 1977a) is unlikely to occur at the southern edge of its distribution in México, particularly in the canyon region of central Jalisco, where deep ravines prevent long distance dispersal and pollination flow and favor allopatric speciation.

Phenology: —The new species is found flowering from September to November, and fruiting from October to January. Deciduousness of foliage at the beginning of autumn (September).

Eponymy: —The specific epithet honors both Doctorate Honoris Causa Luz María Villarreal de Puga (1913- 2013) and M.Sc. Luz María González Villarreal, two outsdanding botanists (mother and daughter) from Universidad de Guadalajara, Mexico ( Fig. 5 G ).

Ethnobotany: —There is no available information on the use of Populus luzae .

Conservation status: — Populus luzae is only known from two ravines: the type locality where it is found with scarce abundance (nearly twenty trees) at Arroyo La Virgen, Zapopan, and a second locality at Arroyo Pajaritos stream, a tributary of Arroyo San Lorenzo (near El Encanto hot springs), where the authors have seen only six trees.According to the IUCN Red List Criteria ( IUCN 2012) used to assess the conservation status, Populus luzae should be categorized as Critically Endangered, because this species has a very small population size (<250 mature individuals, criterion C), an estimated continuing decline (criterion C2) due to high deforestation rate by fires and forest conversion to pasturelands, and the number of mature individuals in each subpopulation is less than 50 (criterion C2(a)(i)).According to criterion D, Populus luzae is categorized as Critically Endangered too, due to its very small and restricted population with <50 known individuals, and it also has a very restricted geographic range (an Area of Occupance “AOO” of less than 10 km 2, criterion B) ( Fig. 8 ). Hence, Populus luzae deserves immediate protection and should be considered a Critically Endangered (CR) tree species. Fortunately, cuttings and seeds are being tried to propagate at the botanical institute of the Universidad de Guadalajara in order to study its biology and its rate of growth.

Additional specimens examined (paratypes): — MEXICO. Municipio Zapopan: Spring of Río Atlicotle, nearby Copala , 1460 m, 7 July 1975 (sterile), Villarreal 7411 ( IBUG: currently lost). Jalisco: Zapopan , Arroyo La Virgen , 1.25 km SW from Rancho San Nicolás , 9 km WNW from Santa Lucía , 20°48’52.38” N, 103°34’53.88”W, 1430 m, 11 January 2013 (sterile), Muñiz-Castro et al. 1157 ( IBUG) ; Zapopan, Arroyo La Virgen, 1.25 km SW from Rancho San Nicolás , 9 km WNW from Santa Lucía , 20°48’52.38” N, 103°34’53.88”W, 1430 m, 26 February 2013 (fallen fr) Muñíz-Castro & Vázquez-García 1164. ( IBUG) ; Zapopan, Arroyo La Virgen, 1.25 km SW from Rancho San Nicolás , 9 km WNW from Santa Lucía , 20°48’52.38”N, 103°34’5 3.88” W, 1430 m, 6 March 2013 (sterile), Nieves et al. s.n. ( IBUG); Zapopan, Arroyo La Virgen, 1.25 km SW from Rancho San Nicolás, 9 km WNW from Santa Lucía, 20°48’52.38”N, 103°34’5 3.88” W, 1430 m, 3 October 2017 (male infl.), Nieves & Padilla-Lepe s.n. ( IBUG, MEXU, ZEA, WIS) ; Zapopan, Arroyo Pajaritos ( San Lorenzo stream) (near El Encanto hot springs), 600 m NW from home of Rancho de Los Rivera (inside the ranch), 6 km W from Santa Lucía , 20°48’39.04”N, 103°33’15.48”W, 1425 m, 19 January 2013 (sterile), Muñiz-Castro et al. 1162 ( IBUG) .

Figures

FIGURE 1. Populus luzae, Habit and bark detail. Illustrations by Daniel Barba.

FIGURE 2. Populus luzae. A. Bract, floral disk and capsule. B. Capsule with floral disk. C. Twig with developing infrutescence. D. Terminal twigwith infrutescense.E.bract with pedicel.F.Seed with arilate coma.G.Developing infrutescence.H.Dehiscing infrutescence. I. Closed and open capsule. J. Close up to open capsule. K. Ovary with styles s and stigmas. L. Variation of leaf shape. A–L. Illustrations by Daniel Barba, from the holotype, except for L (leaves collected from the ground).

FIGURE 3. Populus luzae. A–D. Twigs with leaves and female inflorescences, ruler in cm. E. Twig with developing infrutescences. F. Twig with mature infrutescences with dehiscent capsules and cottony seeds getting out. Photographs A–D by Jesús Padilla-Lepe, E–F by Miguel Muñiz-Castro.

FIGURE 4. Populus luzae. A–B. Ciliated female bracteoles. C–D. Capsules and floral disks. Photographs, all from the holotype, by Miguel Muñiz-Castro.

FIGURE 5. Populus luzae. A. Male inflorescence at anthesis, with fully developed anthers. B–C. Male inflorescence after anthesis. D. Abaxial leaf surface. E. Variation of leaf shape and size, and immature infrutescences. F. Stems form a single individual and newly rootborne shoots. G. Dr. Luz María Villarreal de Puga† and M.Sc. Luz María González Villarreal, both from Universidad de Guadalajara, México. Rulers in cm. Photographs A–B by Jesús Padilla-Lepe, C–F by Miguel Muñiz-Castro, G by Luz María González Villareal.

FIGURE 6. Populus luzae. Holotype, M. A. Muñiz-Castro, J. Padilla-Lepe and A. T. Nuño-Rubio 1150 (IBUG).

FIGURE 7. Populus guzmanantlensis. A. Holotype, R. Cuevas and L. Guzmán 3224 (ZEA). B. An isotype (IBUG). C.A paratype, Cuevas & Guzmán 2930 (IBUG). D. A paratype, Cuevas & Guzmán 2925 (ZEA).

FIGURE 8. Distribution of species of Populus in Jalisco, México. Populus simaroa is added for reference since it is considered morphologically related to P. guzmanantlensis (Dickmann & Kuzovkina 2014).