Mancoa chontaensis Al-Shehbaz, Cano, Machahua, J.Roque & Mazzei, 2025

Al-Shehbaz, Ihsan A., Cano, Asunción, Machahua, Miguel, Roque, José & Mazzei, Piero, 2025, Mancoa chontaensis, a new species from Peru, and a synopsis of the genus Mancoa (Halimolobeae; Brassicaceae), Phytotaxa 701 (1), pp. 121-125 : 121-123

Mancoa chontaensis Al-Shehbaz, Cano, Machahua, J.Roque & Mazzei , sp. nov.

Diagnosis:— Mancoa chontaensis differs from the remaining species of the genus by having narrowly oblong to linear silique, biseriate seeds, and flowers in ebracteate racemes and/or solitary pedicels originating from basal rosettes.

Type: — PERU. Dep. Huancavelica. Prov. Castrovirreyna, [Cordillera Chonta, Distr. Castrovirreyna], Abra , 13°00’17”S, 75°20’46”W, 4873 m, 11 March 2018, Miguel Machahua & José Roque 198 (holotype: USM-354952; isotype, MO-4015216). Figure 1 .

Description:—Herbs prostrate, short lived-perennial, sparsely to moderately puberulent with a mixture of simple and short-stalked, 2- or 4-rayed forked trichomes mixed with fewer subdendritic ones 0.05–0.1 mm long. Stems 4–8 from rosette, 3–8 cm long, procumbent, simple, glabrous or sparsely puberulent with simple and fewer subsessile 2-rayed trichomes, glabrous at plant maturity. Basal leaves rosulate, 1.5–3 cm long; petiole 1–1.7 cm long; blade oblanceolate to spatulate in outline, 1.5–2 cm long, pinnatifid to pinnatipartite, puberulent; lateral lobes 3–7 on each side, ovate to oblong, entire, obtuse, smallest proximally, 1–3 × 1–1.5 mm, terminal lobe obtuse at apex; cauline leaves petiolate, similar to basal ones but smaller and fewer lobed. Inflorescence remaining flat on ground, either exclusively solitary flowers on pedicels from basal rosette or mixed with ebracteate, 8–12-flowered racemes, subcorymbose, hardly or slightly elongated and to 8 cm long in fruit; rachis glabrous, sometimes considerably reduced in length and together with cauline leaves forming a pseudo-rosette; fruiting pedicels glabrous, terete, 0.8–2 cm long, appressed to rachis. Sepals oblong, erect, 2.5–3.5 mm long in flowers becoming 4–5 mm long in fruit, persistent throughout fruit maturity and dehiscence, sparsely pubescent with few trichomes or glabrescent, not membranous at margin; petals creamy white, erect, spatulate, 2.5–4 × 0.8–1.2 mm, rounded at apex, claw 1–1.5 mm long; stamens tetradynamous, median pairs ca. 3 mm long, lateral pair ca. 2 mm long; anthers ovate, 0.1–0.2 mm long; ovules 12–24 per ovary. Fruits linear to narrowly oblong, 15–17 × 2.5–3 mm, length 5–7 times width, subangustiseptate-subterete; valves sparsely pubescent when young with simple and subsessile forked trichomes on valve and/or replum, usually glabrous at maturity, terete, smooth, not keeled or veined; septum complete, membranous; style 0.8–1 mm long; stigma entire. Seeds oblong, plump, wingless, biseriate, smooth, 1.1–1.5 × 0.7–0.9 mm.

Distribution:— Endemic to Peru and known from a handful collections from Cordillera Chonta in Huancavelica Department. Figure 2 .

Habitat:— Grows in cryoturbed soils in alpine areas, recorded at 4870–5020 m asl.

Etymology:— The new species is named after Cordillera Chonta, the mountain range where its two populations were found.

Phenology:— The populations of this species were found flowering and fruiting in January and March.

IUCN preliminary conservation assessment:— Preliminary analyses suggest that Mancoa chontaensis should be included in the Endangered category (EN), according to criteria B2ab(ii,iv) of the IUCN red list (IUCN, 2022). The new species has an area of occupation (AOO) of 8 km 2 (<10 km 2) and its populations occur in two localities belonging to the Cordillera Chonta mountain range. The main threat to this species is the presence of mining activity less than 7 km from its area of occupation. The estimated number of mature individuals per population is approximately 75–100.

Additional specimens examined (paratypes):— PERU. [All collections from Cordillera Chonta] Dep. Huancavelica, Prov. Castrovirreyna, Distr. Castrovirreyna, Abra , cerca de la Laguna Antajocha, 13°00’17”S, 75°20’46”W, 4873 m, 16 January 2025, Machahua & Roque 355, 356 ( USM) ; Distr. Santa Ana, Abra Chonta , 13°04’35”S, 75°03’33”W, 5020 m, 17 January 2025, Machahua & Roque 366, 367 ( USM) .

Discussion:— The description of Mancoa chontaensis expands the generic limits of Mancoa as delimited by Bailey et al. (2007). This necessitates emending the circumscription of the genus as follows. It is easily distinguished from its congeners by having subangustiseptate siliques instead of strongly angustiseptate silicles. This difference in fruit morphology, however, is sometimes trivial because it is found in many genera, including smaller ones such as Tropidocarpum Hook. (4 spp.), Vella L. (8 spp.), Halimolobos Tausch (8 spp.), as well as medium-sized genera, such as Sisymbrium L. (ca. 50 spp.) and Hesperis L. (ca. 52 spp.) and larger ones, e.g. Draba L. (ca. 400 spp.), Heliophila L. (106 spp.). Three of the eight species of Halimolobos produce silicles, and that led Rollins (1976) to place them in Mancoa . They and the other species of Halimolobos are easily distinguished from the other New World genera by having bimodal trichome size of large and much smaller dendritic trichomes on the fruit valves.

The North-South American disjunction of Mancoa is not surprising because it and three other genera of the Halimolobeae ( Exhalimolobos Al-Shehbaz & C.D.Bailey, Pennellia and, Halimolobos) have bicontinental distributions, whereas Sphaerocaramum S.Schauer (4 spp.) is endemic to Mexico and Petroravenia (1 sp.) is endemic to northern Argentina in Catamarca, Jujuy, and Salta Provinces.

Figures

FIGURE 1. Mancoa chontaensis. A. Prostrate fruiting plant with fruiting racemes and solitary fruits on pedicels from rosette center. B. Flowers. C. Leaf trichomes. D. Solitary fruits. Photos by José Roque.

FIGURE 2. Map showing the two collecting localities (stars).