Mixtecalia teitaensis Redonda-Mart., García-Mend. & D. Sandoval, 2020

García-Mendoza, Abisaí Josué, Sandoval-Gutiérrez, Daniel & Redonda-Martínez, Rosario, 2020, Mixtecalia, a new monotypic genus of the subtribe Tussilagininae (Senecioneae, Asteraceae) from the state of Oaxaca, Mexico, Phytotaxa 438 (2), pp. 119-129 : 119-129

Mixtecalia teitaensis Redonda-Mart., García-Mend. & D. Sandoval , sp. nov. ( Figs. 1–4 )

Type:— MEXICO. Oaxaca: distrito Tlaxiaco: municipio San Juan Teita , 500 m al SW del pueblo, 9 November 2017, D. Sandoval et al. 1475 (holotype: MEXU!; isotypes: CTES!, IEB!; K!, MEXU!, MO!, NY!, P!, TEX!, US!).

Folia ovato-elliptica , petiolis ad basem amplectentibus utrinque cinereo-tomentosis. Phyllaria 6–8, oblongo-lanceolata, lanata. Flosculi 10–12. Cypsela 5–6-costata.

Monocarpic arborescent plants, 0.8–4 m tall. Stems simple, erect, terete, pachycaulous, densely lanate. Leaves verticillate, marcescent, absent during the flowering period; with petioles 3.4–7 cm long, overlapping at the base; blades ovate-elliptic, 8.7–13.8(–30) × 7.2–8.4(–20) cm, margin revolute, dentate, acute at the apex, cordate at the base; foliage with indumentum tomentose on both surfaces. Synflorescence paniculiform, with bracts tomentose. Heads discoid, with peduncles short, 7.3–16.8 mm long, lanate; involucre turbinate, 10.6–15.5 × 6–9.2 mm, uniseriate, 6–8 phyllaries, oblong-lanceolate, with a conspicuous rib in the middle, lanate. Calyculus 2.3–4.8 mm long, with 4–6 bracts, linear-lanceolate, lanate. Receptacle flat, alveolate, naked. Florets 10–12 bisexual, corolla infundibuliform, 5-lobed, yellow, 11.2–12 mm long, tube 5.4–6 mm long, glabrous, lobes triangular, 4.7–5 mm long, papillose at the apex. Anthers 3.8–4.1 mm long, apical appendages lanceolate, polar endothecial tissue, base auriculate, cylindrical collar, filaments fused at the base. Style 9–9.5 mm long, branches 1.6–1.8 mm long, obtuse, papillose on both surfaces, stigma surface continuous. Cypselae terete, 5–6-ribbed, 6.2–7.8(–8.2) mm long, sericeous. Pappus uniseriate, 8.8–10 mm long, 195–198 capillary bristles, subequal.

Phenology:—Flowering is from October to January, and fruiting is from February to March.

Etymology:—The epithet refers to San Juan Teita, the name of the municipality where the species is found.

Distribution:— Mixtecalia teitaensis is known only from the San Juan Teita municipality, located in Tlaxiaco, Oaxaca ( Fig. 5 ), where it occupies an area of approximately 1.75 km 2.

Habitat and plant associations:— Mixtecalia teitaensis , Cephalocereus parvispinus Arias, Tapia & Guzmán (2019: 150) and Agave gypsicola García-Mendoza & Sandoval in García-Mendoza et al. (2019: 6) are the dominant species of the xerophytic scrub. This plant association occurs on gypsisols ( Fig. 1A ), which occupy very small areas but host a large number of endemic species (CONABIO 2011). The climate of the San Juan Teita locality where this plant community is located is warm and dry, with rains in the summer. Mixtecalia teitaensis grows at altitudes from 1352–1455 m, on sites with pronounced slopes (70–90°).

Conservation Status:—Based on the IUCN (2017) criteria, Mixtecalia teitaensis , which has an area of occupation (AOO) smaller than 100 km 2 and is found in habitats affected by livestock and extraction activities, could be considered as endangered (EN, criterion B2ab(iii)).

Morphological affinities:— Mixtecalia teitaensis is a distinctive species among the Mexican Senecioneae due to its monocarpic reproductive strategy; arborescent habit; pachycaulous, lanate stems; marcescent leaves, tomentose on both surfaces and absent during the flowering period; and the paniculiform and bracteate synflorescences, which can reach double the size of the plant during reproduction.

The indumentum on the vegetative structures is tomentose on the leaves and lanate on the peduncles, bracts of the synflorescences, and phyllaries of the involucre ( Figs. 1E , 3 , 4A–F ). The indumentum is made up of flagelliform trichomes with 3–4 cylindrical basal cells of equal length and one long filiform apical cell, which is 8–10 times longer than the group of basal cells ( Fig. 4B–C ). In the florets, the lobes of the corolla have papillae at the apex ( Fig. 4H–I ); the branches of the style also have papillae on both surfaces, though they are longer on the outer surface than they are on the inner surface ( Fig. 4M–O ). The cypselae have a sericeous indumentum ( Fig. 4G ), consisting of a large quantity of long twin hairs, which are composed of two elongated conical cells, one of which is slightly shorter than the other. Mixtecalia teitaensis has morphological affinities with other taxa of the subtribe Tussilagininae , in particular with Pittocaulon bombycophole (Bullock) Robinson & Brettell (1973: 452) , Roldana eriophylla (Greenm.) Robinson & Brettell (1974: 418) and Telanthophora grandifolia (J.M. Coult.) Robinson & Brettell (1974: 427) , as well as with Dendrosenecio , a member of the subtribe Senecioninae . Among other characteristics that they share, some of the most notable are: pachycaulous stems, verticillate leaves, turbinate involucres (excepto en D. keniensis ),phyllaries with a conspicuous rib in the middle (except in D. keniensis ), yellow discoid florets, and pappi with white capillary bristles. In addition to the aforementioned characteristics, M. teitaensis has other similarities to P. bombycophole and R. eriophylla , particularly, the absence of leaves during the flowering period, a tomentose indumentum on both surfaces of the leaves, and anthers with lanceolate apical appendages and cylindrical collar. With P. bombycophole it also shares the presence of lanate indumentum on the distal region of the stem and obtuse and papillose style branches, while with R. eriophylla and T. grandifolia it shares turbinate involucres with 8 phyllaries and discoid heads with at least 12 florets. Mixtecalia teitaensis is similar to D. keniensis in its marcescent leaves, tomentose peduncles and paniculiform and bracteate synflorescences; however, it differs in the type of heads (discoid vs. radiate), type of involucres (turbinate vs. campanulate); numbers of phyllaries (18–20 vs. 6–8) and discoid florets (50–60 vs. 10–12), and the shape of the cypselae and indumentum (oblong, and glabrous vs. terete and sericeous). The macromorphology of D. keniensis is the most similar to that of M. teitaensis ( Table 2).

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Despite their shared characteristics, M. teitaensis differs from P. bombycophole , R. eriophylla , T. grandifolia and D. keniensis in that it is a monocarpic plant, a character that, in addition to the filaments of the anthers being fused at the base and the sericeous cypselae, allows it to be recognized as a species that is new to science. Further study is required to understand the population dynamics of M. teitaensis , its ecological interactions with the plants that share its distribution area, the anatomical characteristics of its vegetative and reproductive structures, and its chemical compounds and to clarify its phylogenetic placement within the subtribe Tussilagininae and in the tribe Senecioneae .

Additional specimens examined:— MEXICO. Oaxaca: Tlaxiaco, San Juan Teita, Cerro al SE de San Juan Teita ( NE del panteón), 3 June 2017, A. García-Mendoza et al. 11008 ( IEB!, MEXU!, TEX!) ; 2 km al S de San Juan Teita , 9 November 2017, A. García-Mendoza et al. 11179 ( MEXU!) ; 13 km al S de San Juan Teita, paraje Xuujnuchite [donde hay platanares], camino a Sindihui, 7 March 2018, A. García-Mendoza & S. Franco 11224 ( IEB!, MEXU!, TEX!, XAL!) ; Xee kava [al pie de la peña], 1 km NE de Teita, 13 June 2018, A. López & I. Santiago 160 ( MEXU!) ; Nuu de´vaa [cara de paredón], 3.5 km de Teita , 26 October 2018, A. López & I. Santiago 328 ( MEXU!) ; Xee kava [al pie de la peña], 1 km NE de Teita, 26 November 2018, A. López & I. Santiago 349 ( MEXU!) ; 500 m al SW del pueblo, 3 June 2017, D. Sandoval et al. 1440 ( IEB!, MEXU!) .

Figures

FIGURE 1. Mixtecalia teitaensis. A. Habitat. B. Appearance of young individuals. C. Stem cross section. D. Stem longitudinal section. E. Detail of the synflorescence. F. Details of the involucres and cypselae.

FIGURE 2. Mixtecalia teitaensis. A. Habit. B. Leaf. C. Plant with Synflorescence. D. Synflorescence. E. Primary inflorescence corymbiform. F. Involucre. G. Phyllary apex. H. Ovary with pappus. I. Floret., J. Style. K. Dissected floret. L. Anthers. M. Cypselae with pappus.

FIGURE 3. Holotype of Mixtecalia teitaensis.

FIGURE 4. Microcharacters of Mixtecalia teitaensis. A. Tomentose indumentum of a fragmented leaf. B. Adaxial surface of leaves with tomentose indumentum under SEM. C. Flagelliform trichomes (ft) on the leaf abaxial surface. D. Base of capitula showing the peduncle and calyculus bracts (marked by asterisk *), with indumentum tomentose. E. Phyllary. F. Receptacle flat alveolate. G. Cypsela with sericeous indumentum. H. Corolla lobe apex. I. Details of the corolla lobe apex with papillae (p) under SEM. J. Androecium with filaments fused at the base (asterisk *). K.Anther bases with cylindrical collars. L. Details of the anther showing the polar endothecial tissue (marked by asterisks *). M. Style branches showing obtuse apexes and papillose indumentums. N. Style branch under MEB. O. Detail of style branch apex with papillae (p) on both surfaces.

FIGURE 5. Known geographical distribution of Mixtecalia teitaensis in the state of Oaxaca, Mexico.A. Location of the state of Oaxaca in Mexico. B. Location of the municipality of San Juan Teita in Oaxaca. C. Collection points of M. teitaensis.