The new species is morphologically similar to Senecio pucapampaensis but is clearly distinguished by the leaf lamina oblong-spathulate (vs. cuneiform), leaf surface covered by thin trichomes (vs. glabrous), corolla yellow (vs. white), calycular bracts linear-oblong, 6–9 mm long (vs. linear, 6–7 mm long), and phyllaries 9–12 (vs. 12–14).

PERU. Moquegua Region, General Sánchez Cerro Province, Ubinas District, NW of Tassa, terrestrial on clayey rocky soils on the plateau peaks near Lake Pacosani, elevation 4653 m, 16°06'43"S, 70°44'45"W, 3 April 2009, Montesinos 2400 (holotype USM!, isotypes MO 2383567, HUPCH 4185, CPUN, WAG 0246107).

Perennial herb, rhizomatous, creeping, low-growing, forming mats 2–4 cm tall and up to 60 cm in diam. Trichomes glandular, somewhat dense and irregularly distributed, multicellular, whitish transparent, 0.1–0.3 mm long and 0.05–0.1 mm wide and composed of 4–8 subrotund cells (each 30–50 µm long), apical cell rotund. Stems 1–3 cm long, often densely branched and leafy in the central part, rooting. Leaves cauline, lamina oblong-spathulate, 8–12 mm × 1–2.5 mm, sparsely covered by thin trichomes on the margins, lower and upper surfaces except at the base; base truncated, apex subpinnatifid; young leaves dark green with yellowish margins, turning light green-greyish with age. Synflorescences of solitary sessile or subsessile terminal capitula. Capitula homogamous, discoid. Involucres at first broadly cylindrical, gradually turning campanulate with age, ca. 7–10 mm long × 6–8.5 mm wide). Calycular bracts linear-oblong (6–9 mm × 1–2.5 mm), whitish green on the surface and whitish along the margins, with scarce trichomes near the midrib and margins, apex dark brown covered with short light-brown trichomes. Phyllaries 9–12, connate, 5–8 mm long × 0.7–1.2 mm wide, oblong-lanceolate, covered with thin trichomes sparsely on the surface and densely along the margins, apex greenish grey and dark brown with short white multicellular trichomes. Florets 24–28; corolla tubular, abruptly constricted near the base, 5-lobed, each lobe 0.5 mm long, bright yellow, tube 3–5 mm long × 0.8–1 mm wide; anthers linear-lanceolate, 1.5–2.5 mm long, 0.2–0.4 mm wide, ecalcarate, terminal appendages lanceolate, obtuse, margin whitish transparent and becoming yellow towards the centre; style dark yellow, truncate, papillae covering the whole surface of the apex. Achenes cylindrical, covered with trichomes, 1.8–2.5 mm long and 0.4–0.8 mm wide, light brown; carpopodium symmetrical in a small ring; pappus of smooth bristles, white, silky, 5–6 mm long, with fine single setulae.

Terrestrial plant on clayey rocky soils on the peaks of the highland summits and grasslands in the north of Moquegua Region, at elevations of ca. 4500 to 4800 m. Co-occurring species include Azorella compacta Phil., Calamagrostis vicunarum (Wedd.) Pilg., Pycnophyllum molle Remy, and Festuca spp. Flowers and fruits between March and April.

The specific epithet refers to Moquegua, where the only three collections are known from the north of the department.

(paratypes). PERU. Moquegua Region, General Sánchez Cerro Province, Ubinas District, terrestrial on bare clayey soils in the verges of the road east Pillone town, elevation 4584 m, 16°10'02"S, 70°49'56"W, 24 March 2013, Montesinos 4022 (USM, HUSA). Moquegua Region, General Sánchez Cerro Province, Ubinas District, NW of Tassa, terrestrial on bare clayey soils in the verges of the road to Lake Cochapata, elevation 4687 m, 16°08'56"S, 70°43'0.30"W, 9 December 2013, Montesinos 4200 (CUZ).

A comparison of the material has shown that Senecio moqueguensis is most similar to Senecio pucapampaensis and Senecio tassaensis sp. nov. Together with Senecio evacoides, Senecio expansus, Senecio repens and Senecio humillimus, it forms a coherent morphological and geographical group within Senecio subser. Caespitosi which occurs from central Peru to northwest Argentina and is characterized by the presence of trichomes on stems, leaves and involucres. Senecio moqueguensis can be distinguished from Senecio pucapampaensis by the dense caespitose mat habit, leaves, calycular bracts, corolla color, involucres and achene morphology as summarised in Table 1. Senecio moqueguensis can be distinguished from Senecio evacoides, Senecio expansus and Senecio repens by the habit, density of trichomes, leaf shape and length, as well as by the calycular bracts and phyllary length and form.

Following the criteria and categories of IUCN (2001), a preliminary status of Critically Endangered (CR) is assigned. The new species deserves protection because its total area of occupancy is less than 100 km² (ca. 50 km²) (B1); only three populations are known (B1b); habitat inferred to be continuing to decline (B1b(i-iii)); population estimated to number fewer than 300 individuals (D). The suitable habitats for Senecio moqueguensis on the mountain summits near the set of lakes in the Ubinas district are regarded as endangered because overgrazing of grasslands, changes in annual rainfall, volcanic activity, and exploitation of natural resources may all potentially reduce their extent.

Morphologically similar to Senecio gamolepis but clearly distinguished by the tuft mat habit (vs. cushion mats), the leaf shape being obovate-spathulate (vs. linear-lanceolate), corolla white (vs. yellow), phyllaries 12–14 (vs. 7–9), disc length 7–9 mm (vs. 8–12 mm), and achene length 1.5–2 mm (vs. 1–1.3 mm).

PERU: Moquegua Region, General Sánchez Cerro Province, Yunga District, E of Yunga, terrestrial on bare clayey soils on the peaks of Perusa mountain, elevation 4802 m, 16°11'08"S, 70°38'14"W, 13 April 2012, Montesinos & Calisaya 3805 (holotype USM!, isotype HUSA!).

Perennial herb, decumbent, low-growing and forming small tuft mats 4–6 cm high and up to 6 cm in diam. Trichomes absent. Stems 3–5 cm long, densely leafy, woody and branched at the base. Leaves cauline, alternate, lamina obovate-spathulate, 9–14 mm long × 1–2.2 mm wide, glabrous on surface and margins except at the base (scarcely covered by thin, short trichomes), base truncate to auriculate, apex obtuse, entire, margin involute; young leaves pale green with yellowish margins turning dark green with age. Synflorescences of solitary, terminal capitula. Capitula homogamous, discoid and pedicled (5–10 mm long). Involucres at first narrowly cylindrical becoming cylindrical-campanulate with age (7–9 mm long × 3–5 mm wide). Calycular bracts linear-oblong (6–8 mm × 0.7–1 mm), dark green on the surface and light green along the margins, with dark brown-black apex covered with inconspicuous trichomes or glabrous. Phyllaries 12–14, connate, 5–6.5 mm long × 0.6–1 mm wide, linear-lanceolate, margins glabrous, apex dark brown with short trichomes. Florets 13–16; corolla tubular, abruptly constricted near the base, 5-lobed, each lobe 0.2–0.3 mm long, white, tube 2.5–4 mm long × 0.5–0.8 mm wide; anthers linear-lanceolate, 1.5–2 mm long × 0.2–0.3 mm wide, truncate, terminal appendages lanceolate, obtuse; margin whitish transparent and becoming darker towards the centre; style dark purple, truncate, apically covered by papillae equally distributed. Achenes cylindrical, pale green, finely covered with trichomes, 1.5–2 mm long × 0.6–0.9 mm wide; carpopodium symmetrical in a shallow ring; pappus of smooth fine bristles, white, 4–6 mm long, with fine alternate single setulae.

Terrestrial plant on bare clayey soils on the summits of mountain peaks and grassland plateaus in the north of the Moquegua Region at elevations of 4550–4800 m. Co-occurring with Belloa pickeringii (A. Gray) Sagást. & M.O. Dillon, Nototriche obcuneata (Baker f.) A.W. Hill, Pycnophyllum molle Remy, Senecio candollei Wedd. and Xenophyllum ciliolatum (A. Gray) V.A. Funk. Flowers and fruits between March and April.

This Senecio is named after Karlè Sýkora, a well-known Dutch vegetation scientist who was my mentor in phytosociology.

(paratypes). PERU. Moquegua Region, General Sánchez Cerro Province, Ubinas District, S of Pillone, terrestrial on bare clayey soils in the verges of the road to Pillone town, elevation 4584 m, 16°10'02"S, 70°49'56"W, 24 March 2013, Montesinos 4023 (USM).

Senecio sykorae appears to be closely related to Senecio gamolepis which grows at higher elevations but approaches the known range of Senecio sykorae within a few hundred metres. While Senecio gamolepis is generally distinctive in the genus for its large size, attaining widths of up to 1 meter in diameter, and for its larger, capitulate form, Senecio sykorae is a smaller plant, of about 4–6 cm wide and has shorter corolla, less than 9 mm long. Senecio sykorae is also distinctive in that it has 12–14 phyllaries per capitulum instead of 7–9 phyllaries in Senecio gamolepis. Likely the leaves of Senecio sykorae are distinctive in that they are obovate-spathulate vs. linear-lanceolate. Also, the achenes in Senecio sykorae are larger (1.5–2 mm long) vs. 1–1.3 mm long in Senecio gamolepis. Senecio sykorae also differs from Senecio algens by the leaf and capitula length (shorter in Senecio sykorae), and from both species by the corolla colour (white vs. yellow). Less similarity is found in Senecio algens, Senecio humillimus, Senecio trifurcifolius, Senecio pucapampaensis and Senecio evacoides, and from which Senecio sykorae can be distinguished on the basis of its habit, trichomes, leaf shape and length, calycular bracts and phyllary length and shape as summarized in Table 1.

Following the criteria and categories of IUCN (2001), a preliminary status of Critically Endangered (CR) is assigned. The new species deserves protection because its total area of occupancy is less than 10 km² (ca. 5 km²) (B2); only one population known (B2b); habitat inferred to be continuing to decline (B2b(i-iii)); population estimated to number fewer than 150 individuals (D). The suitable habitats for Senecio sykorae on the mountain summits of the north of Moquegua are indicated as endangered because of overgrazing of grasslands, changes in annual rainfall, volcanic activity, and exploitation of natural resources, all potentially reducing their extent.

Similar to Senecio moqueguensis but clearly distinguished by the leaf lamina obovate-spathulate (vs. oblong-spathulate), leaf length 6–9 mm (vs. 8–12 mm), leaf surface densely covered by trichomes (vs. sparsely covered), trichomes 0.3–1.2 mm long (vs. 0.1–0.3 mm long), corolla white (vs. yellow), calycular bracts 4–6 mm long (vs. 6–9 mm), phyllaries 12–16 (vs. 9–12), involucre length 6–8 mm (vs. 7–10 mm), and achene length 1–1.2 mm (vs. 1.8–2.5 mm).

PERU. Moquegua Region, General Sánchez Cerro Province, Ubinas District, NW of Tassa, terrestrial on clayey rocky soils on the summits of Pirhuani peak, elevation 4657 m, 16°09'58"S, 70°43'49"W, 07 April 2011, Montesinos 3103 (holotype HUSA!, isotypes MOL, USM).

Perennial herb, tufted, up to 2–4 cm high and up to 4 cm in diam. Trichomes glandular, densely covering the plant, multicellular, whitish transparent, 0.3–1.2 mm long × 0.1–0.2 mm wide, composed of 6–10 ovate or elongate cells (each 60–80 µm long), apical cell rotund. Stems thick, < 1 cm long, often densely branched and leafy in the central portion. Leaves arranged in irregular rosettes, lamina obovate-spathulate, 6–9 mm × 1–2.5 mm, densely covered by thin trichomes on the margins; base truncated and apex pinnatifid; lower and upper surface of the leaves gradually becoming shorter towards the tip; margin incised with 5–7 obtuse lobes or rarely acuminate; mature leaves with involute margins; young leaves green yellow turning greenish grey with age. Synflorescences of solitary sessile or subsessile terminal capitula. Capitula homogamous, discoid. Involucres at first cylindrical, turning campanulate with age (ca. 6–8 mm long × 5–7 mm wide). Calycular bracts ovate-oblong (4–6 mm × 1 mm), greyish green on the surface and covered with trichomes on the margins, dark brown apex covered apically with short brown multicellular trichomes. Phyllaries 12–16, connate, 5–8 mm long × 0.8–1.2 mm wide, linear-lanceolate, covered with thin trichomes scarcely on the surface and densely along the margins, apex dark brown and covered with short multicellular trichomes. Florets 18–21, corolla tubular, abruptly constricted near the base, 5-lobed, each lobe 0.2–0.4 mm long, purple pink gradually becoming pale white towards the tip, tube 2–2.5 mm long × 1 mm wide; anthers linear-lanceolate, 1.5–2 × 0.3–0.4 mm, terminal appendages lanceolate, acute to somewhat protuberant, bases ecalcarate; anthers margin white becoming dark yellow towards the centre; style dark purple, truncate, papillae covering the whole surface of the apex. Achenes ovate, striate, covered with trichomes, 1–1.2 mm long and 0.6–0.8 mm wide, pale yellow; carpopodium symmetrical in a shallow ring; pappus of smooth bristles, white, silky, 3.5–5 mm long, with fine single setulae.

Terrestrial plant on clayey rocky soils on the peaks of the highland summits of the Pirhuani peak, near Tassa town, Moquegua Region, at elevations of 4650–4700 m. It occurs with Azorella, Calamagrostis, Pycnophyllum, Mniodes, Senecio, and Xenophyllum. Flowers and fruits between March and April.

This Senecio is named after the town of Tassa (Moquegua Region), downslope of Pirhuani peak where the species was found.

Senecio tassaensis appears to be closely related to Senecio moqueguensis which grows at the same elevational range but approaches the known range of Senecio tassaensis within a few hundred metres. Senecio moqueguensis is generally distinctive in the series for its larger size, attaining dense ground mats, and for its yellow corolla. Senecio tassaensis has 12–16 phyllaries (vs. 9–12), an involucre length of 6–8 mm and achene length of 1–1.2 mm, being much shorter than in Senecio moqueguensis. Senecio tassaensis is relatively a very rare species with an estimated 100 individuals known. It is less similar to Senecio pucapampaensis, Senecio evacoides, Senecio expansus and Senecio repens, and can be distinguished on the basis of the habit, trichomes, leaf shape and length, calycular bracts and phyllaries length and shape as summarized in Table 1.

Following the criteria and categories of IUCN (2001), a preliminary status of Critically Endangered (CR) is assigned. The new species deserves protection because its total area of occupancy is less than 10 km² (ca. 5 km²) (B2); only one population is known (B2b); habitat inferred to be continuing to decline(B2b(i-iii)); population estimated to number fewer than 100 individuals (D). The suitable habitats for Senecio tassaensis on the mountain summits of Pirhuani peak in the Ubinas district are indicated as endangered, because changes in the annual rainfall, volcanic activity and exploitation of natural resources, may all reduce their extent.