Pachyphytum odam Art. Castro & P. Carrillo

Castro-Castro, Arturo, Ortiz-Brunel, Juan Pablo, Ávila-González, Heriberto, Lichter-Marck, Isaac H., Carrillo-Reyes, Pablo, López-Enríquez, Irma Lorena & Barvosa-Jiménez, Marco Antonio, 2023, Spatial richness analysis and an evaluation of extinction risk for the genus Pachyphytum (Crassulaceae), with the description of a new species from Sierra Madre Occidental, Mexico, Phytotaxa 629 (3), pp. 197-209 : 204-207

Pachyphytum odam Art. Castro & P. Carrillo , sp. nov., Figure 3

Diagnosis:— Pachyphytum odam is morphologically similar to P. contrerasii , P. kimnachii , P viride and P. werdermannii due to the length of the stems, the shape of the leaves, the size of the fertile bracts, and the petals with an abaxial red spot in the middle. From P. contrerasii and P. viride , it differs in possessing a shorter and more compact cincinnus, larger calyx lobes of a distinct shape, and the size, shape and color of the petals, filaments, and style. From P. kimnachii it differs principally in the shape, size and length of leaves, peduncle bracts, cincinnus, and stamens, and in the number of flowers. Finally, P. odam can be differentiated from P. werdermannii by the peduncle and floral bract shape, the color of the cincinnus and corolla lobes, and the length and color of antipetalous stamens.

Type:— MEXICO. Durango. Mezquital: Comunidad de Santa María de Ocotán y Xoconoxtle , Anexo La Muralla , elev. 2115 m, 14 March 2019 (fl, fr), A. Castro-Castro et al. 4442 (holotype CIIDIR!, isotypes IBUG!, MEXU!, SLPM!) .

Description:— Suffrutescent herb, succulent, pendant, decumbent, glaucous, glabrous; stems often unbranched or branched from near the base, 30‒60 cm long, 1.4‒1.8 cm thick, adventitious fibrous roots and conspicuous leaf scars at the nodes. Leaves 12‒26, sessile, arranged in a disordered spiral at the apex of the stem, in lax rosettes, laminas elliptic or obovate, (4.5‒)6‒10.5 × (1.5‒) 2‒3.5 cm, 6.5‒10 mm thick, elliptical-concave in cross section, conspicuous rib on dorsal surface, apex rounded, margin entire, succulent, pale green to pale reddish to pinkish orange, slightly pruinose, glabrous. Inflorescence axillary, near the apex of the branches; peduncle 15‒26 × 0.4‒0.6 cm, pale reddish to pinkish orange, pruinose; sterile bracts 2‒3, deciduous, ovate, 12‒22 mm × 5‒12 mm, acute, obtuse-cuneate, flat, pale reddish to pinkish orange; cincinnus 8‒9 cm long, 15‒18 flowers, pale green, slightly pruinose; flower bracts imbricate, ovate, 10‒20 × 5‒14 mm, acute to slightly apiculate to mucronate, obtuse-oblique, green, yellowish green to pinkish orange with maturity. Flowers on a turbinate pedicel, 3‒7 mm × 2.5‒4 mm, green, pruinose. Calyx 5-lobate, lobes unequal, the largest oblong, 15‒18 × 7‒9 mm; the smaller oblong, 10‒13.5 × 3.2‒5.5 mm, both acute, mucronate, obtuse. Corolla 5-lobate, lobes oblong, 7.5‒11 mm × 3.5‒4.3 mm, apex acute, white with a broad ventral bright red spot in the middle; appendages obtuse, red. Stamens 10, flattened, 5 antipetalous, 4‒5 mm long, 5 antisepalous, 6‒7 mm long, white with red apex; anthers 1.9‒2.1 × 0.9‒1 mm; pollen pale yellow. Nectaries transversely elliptical, 2.2‒2.5 mm long, pale yellow. Ovary 6‒6.5 mm long; style 7‒8.5 mm long. Follicles 7.5‒8 mm long. Seeds numerous, clavate to pyriform, 0.5‒0.6 × 0.19‒0.22 mm.

Distribution and habitat:— Pachyphytum odam grows on north facing cliffs bordering the wide and deep canyon of the river El Navío (Mezquital municipality, Durango), in which one of the only two known populations of Pinus maximartinezii Rzed. (1964: 17) also occurs ( González-Elizondo et al. 2011). The area is dominated by Pinus-Quercus forest, where, in addition to P. maximartinezii , the following trees occur: Arbutus madrensis S. González , A. tessellata P.D. Sørensen, ex Klotzsch, Fraxinus sp. , Pinus lumholtzii B.L. Rob. & Fernald , Quercus chihuahuensis Trel. , Q. gentryi C.H. Mull. , Q. praeco Trel. , Q. resinosa Liebm. and Yucca sp. Associated shrubs include Ageratina spp. , Arctostaphylos pungens Kunth , Chiococca sp. , Comarostaphylis polifolia (Kunth) Zucc. , Lagascea helianthifolia Kunth , Montanoa sp. , Opuntia spp. , Rhus aromatica Aiton , Salvia melissodora Lag. , Stevia sp. , and Vernonia sp. Other plant species that grow in association with P. odam on vertical rock outcrops are Agave schidigera Lem. , Dasylirion sp. , Ferocactus histrix (DC.) G.E. Linds. , Ficus petiolaris Kunth , Hechtia sp. , Mammillaria sp. , Muhlenbergia sp. , Nolina sp. and Tillandsia sp. ( Figure 4 ). It occupies an elevational range from 2080 to 2115 m ( Table 2 ).

Phenology:— Pachyphytum odam flowers and fruits in March. However, under cultivation in Durango city, the plants began to flower as early as December and continued until March.

Additional specimens examined: — Mexico. Durango: Mezquital: La Muralla, Reserva Comunitaria del bosque de Pinus maximartinezii , 1733 m, 15 March 2021 (fl, fr), A. Castro-Castro et al. 4699 (CIIDIR, IBUG, MEXU).

Conservation status:— Pachyphytum odam is known from the type location, where we have documented approximately 30 mature individuals. Members of the O’dam nation, on whose land P. odam occurs, have informed us that the species is rare and that they are unaware of other populations. Based on AOO results and following the IUCN criteria B2 (area of occupancy estimated to be less than 10 km 2 and known to exist at only a single location), we preliminarily propose that it be designated as critically endangered (CR/B1a).

Etymology: — The specific epithet honors the O’dam people or Southern Tepehuán, on whose land the new species grows.

Vernacular name:— Pachyphytum odam is known to members of La Muralla community as da’npakal, an O’dam word that can be translated as bald, naked, or slippery, perhaps alluding to the glabrous leaves and stems.

Figures

FIGURE 3. Pachyphytum odam Art. Castro & P. Carrillo. A–B. Lateral and front view of the flower. C. Lateral view of the rosette. D. Calyx lobes. E. Corolla lobes. F. Transverse view of the ovary. G. Lateral view of the androecium and gynoecium. H. Petal abaxial view. I. Lateral view of the corolla without the calyx. J–K. Lateral and adaxial view of the cincinnus. Photographs:Arturo Castro Castro.

FIGURE 4. Habitat (A–C) and habit (D) of Pachyphytum odam Art. Castro & P. Carrillo.