Acanthocereus atropurpureus P. González-Zamora & Dan. Sánchez, 2021

González-Zamora, Pedro, Rodríguez-Contreras, Aarón & Sánchez, Daniel, 2021, A new endemic species of Acanthocereus (Cactaceae) from southern Jalisco, Mexico, Phytotaxa 522 (2), pp. 131-138 : 132-137

Acanthocereus atropurpureus P. González-Zamora & Dan. Sánchez , sp. nov. ( Figs. 1–2 ).

Type:— MEXICO. Jalisco: Municipio de Zapotitlán de Vadillo, Armería river basin, 19.510138° N, 103.879422° W, 700 m a.s.l., 07 June 2019, González-Zamora 08 (holotype IBUG!, isotype MEXU!) .

Diagnosis ( Table 1 ): — Acanthocereus atropurpureus has ribbed and non-maculated green stems, which turn purple in dry season, whereas A. tepalcatepecanus displays cylindrical non-ribbed and maculated stems. A. atropurpureus presents thinner stems with smaller spines, comparing to A. castellae and A. cuixmalensis (0.8–1.6 cm stem diameter and 0.9–1.3 mm spine length vs. 1.9 –3.0 cm and 5–25 mm vs. 1.8–3.5 cm and 7–15 mm). Finally, A. atropurpureus can be distinguishable from A. paradoxus because of the first presents thicker stems (0.8–1.6 mm vs. 0.5–0.9), stems are triangular or quadrangular in cross section (vs. cylindrical), and have sinuated ribs margins (vs. straight ribs margins only noticeable during the dry season).

Description: —Shrubs, semi erect or decumbent plants, 0.7–2.0 m tall. Root tuberous, 15–25 cm long, 15 cm in diameter. Stems dimorphic and articulate; young stems 5–6 ribbed, areoles round, up to 1.7 mm length and diameter, 2–9 mm apart; spines 8–12, acicular, 1–5 mm long; adult stems arcuate, with 3–4 low ribs with sinuate margins, 0.9– 1.6 cm in diameter, dull green in rainy season, turn pale pink or purple during the dry season; areoles round, 1.4–2.0 mm length and diameter, 3.5–4.4 cm apart; central spines bulbous, 4, 0.9–1.4 mm long; radial spines 2, acicular, adpressed at the inferior part of the areole, 1.2–3.5 mm long. Flowers nocturnal, infundibuliform, 9–10 cm long, 8.5 cm in diameter at the perianth; pericarpel 1.3–1.8 cm long, receptacular tube 6 cm long, both bearing small areoles with white short trichomes, spines thin, acicular, up to 9, 1– 3 mm long; outer tepals reddish brown and yellowish white, reflexed; inner tepals cream to white, inclined to ascending; stigma slightly exerted. Fruits piriform to oblong, dark red and purple, 5.0– 5.5 cm long, 3.0– 3.5 cm diameter, areoles persistent, with acicular spines up to 10, 8 mm long. Seed broadly oval, 3.5 mm length, 2.3 wide, black-brown, glossy.

Etymology: —The specific epithet refers to the non-maculated purple color of the new and older stems under dry conditions.

Vernacular name: —Queen of the night (local name).

Phenology: — Acanthocereus atropurpureus blooms for one night, from May to June, whereas fruits occur from June to mid-August.

Distribution and habitat: — Acanthocereus atropurpureus is endemic to Jalisco ( Mexico), and it occurs along the western limit of the Biosphere Reserve Sierra de Manantlán. It grows on both sides of the Ayuquila-Armería river basin, on slopes of fluvial sedimentary materials in the dry deciduous forest ( Rzedowski 1978) at 650–750 m a.s.l. Climate is sub-humid warm (code “Aw0”) according to García (2004). There were no records of A. atropurpureus downstream the Ayuquila-Armería river basin in the Colima state. Common elements of the vegetation are Bursera kerberi Engler (1883: 41) , Euphorbia macvaughii Carvajal & Lomeli Carvajal (1981: 189) , Pithecellobium dulce (Roxburgh 1798: 67) Bentham (1844: 199) , Jacaratia mexicana Candolle (1864: 420) , Matelea cyclophylla ( Standley 1924: 1191) Woodson (1941: 233) , and various cacti as, for instance, Stenocereus queretaroensis (Weber 1891: 27) Buxbaum (1961: 12) , Pachycereus pecten-aboriginum Britton & Rose (1909: 422) , Isolatocereus dumortieri ( Scheidweiler 1837: 220) Backeberg (1942: 47) , Mammillaria beneckei Ehrenberg (1844: 833) , Acanthocereus tetragonus , Opuntia decumbens Salm-Dyck (1834: 361) , and Pereskiopsis diguetii ( Weber 1898: 166) Britton & Rose (1907: 332) .

Conservation status: — Acanthocereus atropurpureus is only known from one locality. We estimated that the population is composed of 25 adults and 38 juvenile plants, occupying an area of about 3.5 km 2. However, this locality presents grazing, land-use change for farming, which causing erosion and drag of plants. It is common to find individuals with exposed roots caused by the presence of goat and beef cattle, which are eroding the slope surface and nibbling mature stems. Following the categories and criteria of IUCN Red ( IUCN S. S. C. 2019), we proposed A. atropurpureus as critically endangered ( CE), on the basis of the EOO, 25 km 2 (criterion B1 ) and AOO of 3.5 km 2 (criterion B2 ). In addition, it is only known for one locality [condition (a)], presents a bad quality of habitat [(b)(iii)] and the population size is estimated to number fewer than 50 mature individuals (criterion D) .

Taxonomic notes: — Acanthocereus atropurpureus displays a unique combination of characters that allow to discriminate it from the other closely related species. Mature stems up to 1.6 cm in diameter (1.3 cm on average), with 3–4 well-defined low ribs with sinuate margins, and bearing small globular spines up to 1.5 mm (1.2 mm on average) in length. In contrast, A. cuixmalensis and A. castellae have wider stems,> 1.8 cm (on average, 2.1 cm and 2.2 cm, respectively) with 3–4 well-defined high ribs, both species bearing thicker and larger central and radial spines (> 5 mm) ( Fig. 3A ). The geographically closest species A. paradoxus has slightly ribbed to cylindrical thinner stems (0.86 cm on average). Also, orientation of the inner tepals in A. paradoxus is reclined to descending (reflexed), meanwhile in A. atropurpureus is inclined to ascending ( Fig. 3B ). Observation of several plants in floral anthesis all night long has corroborated those differences in floral morphology, which probably are related with a specific pollinator. Although populations of A. atropurpureus and A. paradoxus are only 15 km distant each other, the physiographic characteristic of the region allowed them to evolved in distinct type of climate. Acanthocereus atropurpureus is distributed in subhumid warm climate (Aw0), while A. paradoxus inhabits a semi-arid warm climate BS1(h’)w. Those climates show significant differences in the annual precipitation with 930.8 mm and 555.1 mm; and mean annual temperature of 25.2 °C and 22.1 °C, respectively ( García 2004). Note that precipitation and temperature are the most important variables determining ecological niche in cactus species ( Mosco 2019). Plants of A. atropurpureus and A. paradoxus growing at the greenhouse, with the same temperature and watering frequency, maintain the morphological differences observed on the plants at the field ( Fig. 3 I-L). The southern portion of Jalisco composed of valleys and canyons has promoted the diversification of some groups of plants. The morphology of young stems and geographical distribution suggest that A. atropurpureus , A. castellae , A. cuixmalensis , and A. paradoxus make up a monophyletic group. However, phylogenetic analyses are necessary to corroborate the mode of speciation and relationships of those species.

A taxonomic key for the ribbed and non-maculated species of Acanthocereus from Jalisco and adjacent areas follows.

1. Adult stems with high ribs and straight margins, never circular in cross-section ..............................................................................2

- Adult stems with low ribs and sinuate margins or cylindrical stems, circular or triangular in cross-section ....................................4

2. Adult stem 4–9 cm diameter, longest central spine up to 4 cm, flower 14–20 cm long ............................ Acanthocereus tetragonus

- Adult stem <4 cm diameter, longest central spine <3 cm, flower <13 cm long..............................................................................3

3. Adult stem 3 ribbed, central spines 3–5, stem not maculated ....................................................................... Acanthocereus castellae

- Adult stem (3–)4–5(–6) ribbed, central spines 1, stem slightly maculated during drought season ..................................................... ................................................................................................................................................................ Acanthocereus cuixmalensis

4. Adult stem non-ribbed, with 3–4 straight ribs margins when dehydrated, 5–9 mm stem diamete ...................................................... .................................................................................................................................................................... Acanthocereus paradoxus

- Adult stem ribbed, with 3–4 sinuate ribs margins, 8–16 mm stem diameter ....................................... Acanthocereus atropurpureus

Additional specimens examined:— Acanthocereus paradoxus . MEXICO. Jalisco: Mpio. Tolimán , 13 June 1998, Cházaro & Cortés 7808 ( IBUG) ; 06 June 2019, González-Zamora 7 ( IBUG!) ,

Acanthocereus castellae . MEXICO. Colima. Manzanillo, poblado Chandiablo, brecha Santiago-Chandiablo-Huiscolote , 120 m, 23 Jul 1984, Santana & Cervantes 326 ( IBUG) . Guerrero. Acapulco, La Venta ( Ambrosio Figueroa ), 15 Apr 1973, H. Kruse 3092 ( MEXU) . La Unión, aprox. 24 km NE de las Juntas de los Ríos , carr. La Unión-Coahuayutla, 15 May 2011, Soto-Nuñez 18684 ( MEXU) . Michoacán. Aquila, Marialitos , 60 m, 13 Oct 1990 , Guerrero C. 1214 ( MEXU) . Coalcomán, ca. 58 km entre Coalcomán y Villa Victoria , 2 Jul 1990, Arias et al. 823 ( MEXU) . Arteaga, entre Arteaga y Playa Azul , 490 m, 05 May 1971, Sánchez-Mejorada 71-0509 ( MEXU) ; 06 May 1971, Sánchez-Mejorada 71-0506 ( MEXU)

Acanthocereus cuixmalensis . MEXICO. Jalisco. La Huerta, Bahía Cuixmala, por la ribera del río Cuixmala , a 1 km de la desembocadura, 15 m, 30 Mar 1986, Arreola-Nava 152 ( IBUG) ; Estación Biológica, Chamela, eje central, 85 m, 30 Jun 1982, Lott 1125 ( MEXU) ; 09 Jul 2001, Gómez-Hinostrosa 1987 ( MEXU) ; Playa Careyitos, 10 Jul 1986, Ayala 795 ( MEXU) ; Playa Blanca de Careyitos , creciendo en cantiles, Nov 1969, Sánchez-Mejorada 69-1101 ( MEXU) ; Rancho Cuixmala, lomerío cercano al mar, entre la selva tropical, 45 m, Nov 1969, Sánchez-Mejorada 69- 1101 ( MEXU) ; Rancho Cuixmala, a la orilla del Río Cuixmala , 11 Nov 1969, Tomatlán, Sánchez-Mejorada 69-1101 ( MEXU) ; Playón de Mismaloya , 10 km al N del campamento de pesca de la población de Loreto, 5 m, 11 Mar 1988, Arreola-Nava 906 ( IBUG) , El Tamarindo, 1 km al N del club privado El Tamarindo, 30 m, 31 May 1997, Arreola-Nava 1462 ( IBUG) .

Acanthocereus tepalcatepecanus . MEXICO. Jalisco. Jilotlán de los Dolores, 14 km delante de Tazumbos hacia San Antonio, 620 m, 14 Oct 1984, Arreola-Nava 98 ( IBUG) . Michoacán. Carácuaro de Morelos, sobre el camino de Erendira a Carácuaro, 730 m, 04 Jul 1992, Arias et al. 985 ( MEXU) . La Huacana, Rancho La Caja , a 4 km al SE del km 9 de la carretera Zicuirán-Nuevo Churumuco, creciendo en selva baja caducifolia sobre ladera rocosa, 23 Jul 2010, Soto-Núñez et al. 18216 ( MEXU) . Arteaga, Infiernillo, 5 km al NW del poblado, creciendo en matorral crasicaule en cuenca del río Tepalcatepec , 300 m, Ago 1970, Sánchez-Mejorada 70-0701 ( MEXU) .

Figures

FIGURE 1. Acanthocereus atropurpureus. A: habitat, habit, and growth form. B: morphology of the adult stem. C: thickened root. D: areole and spination. E: morphology of the young plant. F: mature stem with nocturnal anthesis of the flower. G: external morphology of the flower. H: longitudinal section of the flower. I: immature fruit. J: external morphology of the mature fruit. K: longitudinal section of the fruit.

FIGURE 2. Illustration of Acanthocereus atropurpureus. A: habit and growth form. B: detail of the mature stem. C: cross-section of the mature stem. D: areole and spines. E: young plant (from seedling). F: close-up of the young stem (new growth from the mature stem). G: close-up of the flower bud. H: longitudinal section of the flower. I: fruit attached to the stem. J: longitudinal section of the fruit. K: seed and close-up of the testa seed.

FIGURE 3. Comparison of mature stem and flower morphology of Acanthocereus atropurpureus and close species.A and E: A. castellae. B and F: A. atropurpureus. C and G: A. cuixmalensis. D and H: A. paradoxus. I: Plantlets of A. atropurpureus (top) and A. paradoxus (bottom). J: Growing apices of A. atropurpureus (top) and A. paradoxus (bottom). K: Mature stems of A. atropurpureus (left) and A. paradoxus (right) under hydric stress. L: Mature stems of A. atropurpureus (left) and A. paradoxus (right) stems under continuous watering.