Amaranthus neei Pratt

Pino, Ivonne Sánchez-Del, Pratt, Donald & Flores-Olvera, Hilda, 2017, A new species of Amaranthus (Amaranthaceae) from Mexico, Phytotaxa 291 (3), pp. 201-208 : 202-206

Amaranthus neei Pratt , Sánchez-del Pino, & Flores Olv., sp. nov. ( Figs. 1 ‒ 2 )

Type:— MEXICO. Puebla: San Miguel Zoapan, northwestern slopes of Pico de Orizaba. Ruderal in the village, does not seem to be a weed of surrounding maize fields. 19°05’N, 97°21’W, 2900 m.a.s.l., 7 September 1986, Nee 33033 (holotype MEXU!, isotypes CANB, MO, NY, TEX, WIS, XAL!).

Diagnosis:—Monoecious, annual herbs, up to 75 cm long. Stems erect or branched from the base or above, deeply furrowed, reddish to brown, sparse pubescent with uniseriate trichomes, becoming dense near the synflorescences. Leaves alternate, green (sometimes reddish), glabrous, petiolate [petioles 5–45(–50) mm long], estipulate, sometimes with purple V-shaped marks on young leaves; blade ovate [(5–)15–100 × (5–) 7–55 mm], apex acute (sometimes obtuse) and mucronulate or mucronate, base attenuate-cuneate. Synflorescence an indeterminate heterocladic thyrse, 0.5– 15.0(–25.0) cm long with dichasial partial synflorescences. Flowers unibracteate, bibracteolate; bract and bracteoles lanceolate (1.5–2.5 × 0.4–0.8 mm), membranous, brown, green to reddish, conduplicate and enclosing developing, immature flowers, apex pungent, erect or recurvate, decurrent along midrib; midrib 1.6–3.0 mm long, greatly exceeding the bract lamina, flowers, and fruits. Perianth uniseriate. Staminate flowers with 4 or 5 well-developed sepals; outer sepals 1.6–2.4 × 0.5–0.7 mm, slightly conduplicate, cup-like, enfolding the other three, midrib not evident; inner sepals 1.5–2.8 × (0.2–) 0.4–0.6 mm, flat, in an overlapping ring around the stamens, ovate, oblong to linear, midrib not evident. Stamens (2–)4–5. Pistillate flowers without sepals or with (2–)3–5 sepals consisting of minute flaps of tissue to well-developed; outer sepals 0.4–0.6 (in fruit 0.8–1.1) × 0.1–0.4 (in fruit 0.2–0.4) mm, inner sepals 0.4–0.5 (in fruit 0.7–0.9) × 0.1 (in fruit up to 0.4) mm, closely adpressed against the utricle and of the same colour, usually not evident without close examination; ovate, oblong to linear, apex acute to obtuse, base truncate, midrib absent or present. Ovary uniovulate (0.6–1.0 × 0.4–0.6 mm); style absent; stigmas 2–3, 0.4–1.0 mm long, feathery, often poorly preserved in fruit and appearing short due to breakage. Fruit as a single-seeded utricle, ovate to orbicular [1.5–2.2 × (1.0–) 1.2–1.6 mm], papery, bladder-shaped; circumscissile, irregularly dehiscent or indehiscent, sometimes polymorphic on a single individual. Seed 0.75–1.50 mm diameter, lustrous, brown or black, lenticular; embryo annular.

Etymology:—The epithet neei is dedicated to Dr. Michael Nee for his work in plant taxonomy. Dr. Nee collected the specimen assigned as the type of this species.

Vernacular names:— Amaranthus neei is known in the Valley of Mexico as “chia”, “quintonil” and “quiltonil”. In Capácuaro (Michoacán) it is known as “parxn”.

Phenology:—Flowering and fruiting times September ‒ December; old fruits with probably viable seeds are persistent in plants through March.

Habitat:—The species grows in primary and disturbed vegetation in xerophytic scrub, oak, and pine forest. It also grows along roadsides or in cultivated fields, and in salty soils (elevation 2250–2900 m. a.s.l.).

Distribution area:— Amaranthus neei is an endemic Mexican species growing at the Valley of Mexico (South of Hidalgo, Mexico city and State of Mexico), Michoacán, Puebla, Veracruz and Chiapas ( Fig. 3).

Conservation status:— Amaranthus neei has a wide distribution through the Valley of Mexico, Michoacán, Puebla, Veracruz and Chiapas, frequently growing in disturbed vegetation, and falls under the category of Least Concern (LC), following IUCN (2012) criteria.

Taxonomical notes:—On the basis of our careful examination of specimens, Amaranthus neei was confused with A. hybridus and A. hypochondriacus , or labeled as Amaranthus sp. The type collection was identified as “ A. hybridus vel aff.”, thus indicating uncertainty of the specimen’s affinities, and one of the isotypes (WIS) bears an annotation label identified as A. hybridus .

The diagnostic features of Amaranthus neei are its long bracts and minute (2–)3–5 to absent pistillate sepals which lack an evident midrib. This species has also laminas reduced in bracts and bracteoles and short thyrses. A. neei is morphologically similar with the cultivated grain amaranths, especially A. hybridus , A. caudatus , and A. cruentus ( Table 1). Sepal size is similar among these three species, however sepals are shorter in A. neei or absent.

The subgeneric position of Amaranthus neei is not a simple issue since this species diplays a mix of features from subgen. Amaranthus , subgen. Acnida , and subgen. Albersia sect. Pyxidium according to Mosyakin & Robertson (1996) ( Table 2). Subgenus Amaranthus and subgenus Albersia sect. Pyxidium has been recognized on the basis of the fruit dehiscence, while into the subgen. Acnida fruit is always dehiscent except for A. bouchonii ( Wilkin 1992, Mosyakin & Roberston 1996, Costea et al. 2001), and for A. hybridus , which has been occasionally observed to have irregularly dehiscent fruits within a population, or even in the same plant (Costea et al. 2001). A. neei shows fruit dehiscence, irregularly dehiscent or indehiscent. However, it is possible the individuals of A. neei with irregularly dehiscent fruits are less mature than plants with dehiscent utricles. Some specimens seem to have nevertheless indehiscent fruits with mature seeds. As a consequence, it is possible that the dehiscence character of A. neei is not related to plant maturity. Further studies need to confirm this hypothesis.

Concerning the inflorescence structure, most of the members belonging to the sect. Pyxidium display axillary dichasia, while some species ( A. blitum , A. tricolor , and A. viridis ) show terminal synflorescences, which are supposedly characteristic of the subgen. Amaranthus ( Eliasson 1988, Mosyakin & Robertson 1996). Some specimens [Nee 33066 (NY)] appear to be intermediate between A. hybridus and A. neei from the morphological point of view, underscoring the potential relationship between these two species (hybridization?). However, a relationship between the monoecious A. neei and the dioecious subgen. Acnida cannot be ruled out. Recent phylogenetic work on Amaranthus indicated that subgen. Acnida may be polyphyletic, and that there has been at least one reversal from dioecy to monoecy in the North American Atlantic coast species A. pumilus Rafinesque (1808: 360 ; see Waselkov 2013). Some members of subgen. Acnida show variable patterns of dehiscence and sepals very similar to those here reported for A. neei ( Pratt & Clark 2001) . Furthermore, hybrids are known to form between A. hybridus and species belonging to the subgen. Acnida ( Pratt 1999, Tranel et al. 2002, Trucco et al. 2009). Based on these trends, an affinity between A. neei involving either a reversal to monoecy or a hybrid origin between members of subgenera Acnida and Amaranthus is possible.

Amaranthus neei highlights the need for further analysis of infrageneric classifications within Amaranthus . We therefore decline to place A. neei within any of the current sugeneric rank proposed by Mosyakin & Robertson (1996) as the diagnostic character given by these author (inflorescence structure, pistillate sepals number, and fruit dehiscence) appears to be uncertain from the taxonomical point of view. In addition, some authors (e.g., Iamonico 2015) indicated that the classification of Mosyakin & Robertson (1996) is somewhat tenuous and that new taxa at section and subsection levels could be described.

Specimens examined:— MEXICO. Chiapas: Mpio. Tenejapa, Paraje Matsab, 05 October 1966, Alush Shilon Ton 1313 (MEXU). Mpio. Tenejapa, Paraje Sholeh 12 January 1966, Alush Shilon Ton 536 (MEXU). Mpio. Tenejapa, in the colonia ‘Ach’lum 10 October 1966, Alush Shilon Ton 1373 (MEXU). Yalichín, Pilalchen, Chamula, 09 December 1988, López & Martínez 749 (MEXU). Mpio. Zinacantán Valley floor in Zinacatán center, 05 April 1966, Laughlin 610 (MEXU). México city: Delegación Tlalpan, Topilejo, 2650 m, 27 November 1976, Ventura 2426 (ENCB, MEXU). Colonia San Jacinto, 22 April 1962, Villegas 12 (ENCB). W of Huipulco, 2250 m, 09 November 1963, Villegas 266 (ENCB). Barranca de Solís Grande, Lomas Altas de Chapultepec, 20 November 1962, Huerta s.n. (ENCB). Hidalgo: Mpio. Zempoala, Zempoala, 2450 m, 28 September 1975, Ventura 339 (ENCB). State of Mexico: 6 km al N de Huehuetoca, 2300 m, 18 October 1972, Aguilar s.n. (ENCB). Mpio. Texcoco, experimental fields of the Autonomous University of Chapingo, 16 October 1976, Bolaños 75, 77 (MEXU). Coacalco de Berriozabal, 01 February 1977, Espinosa 8 (MEXU). San Miguel Xaltocan, 10 March 1977, Espinosa 93 (MEXU). Cráter del Volcán Loma Larga, Temamtla, 2850 m, Ibarra 14 (MEXU). Zumpango, San Juan Citlaltepec, orilla N del lago de Zumpango, 09 November 1975, Barrios 102 (ENCB). Michoacán: Sansungua Capácuaro, 04 September 1967, Rees & Bille 1334 (MEXU). Puebla: Mpio. Zacapoaxtla, Comaltepec, 20 January 2010, Mapes & Basurto 1201 (MEXU). Mpio. Zautla, San Miguel Tenextatiloyan, 18 December 2009, Mapes & Basurto 1192 (MEXU). Veracruz: Altotonga, 07 June 1974, Ramos & Fernández R-58 (F).

Figures

FIGURE 1. Amaranthus neei. a. Plant; b. Composite view of synflorescence; d, e Staminate flower. c, f, g; Pistillate flower; h. Indehiscent and dehiscent fruit, exploded view.

FIGURE 2. Holotype of Amaranthus neei (MEXU!).