Three new caespitose species of Senecio (Asteraceae, Senecioneae) from South Peru

Abstract Three new species of the genus Senecio (Asteraceae, Senecioneae) belonging to Senecio ser. Suffruticosi subser. Caespitosi were discovered in the tributaries of the upper Tambo River, Moquegua Department, South Peru. Descriptions, diagnoses and discussions about their distribution, a table with the morphological similarities with other species of Senecio, a distribution map, conservation status assessments, and a key to the caespitose Peruvian species of Senecio subser. Caespitosi are provided. The new species are Senecio moqueguensis Montesinos, sp. nov. (Critically Endangered) which most closely resembles Senecio pucapampaensis Beltrán, Senecio sykorae Montesinos, sp. nov. (Critically Endangered) which most closely resembles Senecio gamolepis Cabrera, and Senecio tassaensis Montesinos, sp. nov. (Critically Endangered) which most closely resembles Senecio moqueguensis Montesinos.


Introduction
Senecio contains about 175 species in Peru (Brako andZaruchi 1993, Vision andDillon 1996) including several recently described new species (Beltrán 2009). Th e genus has 94 species endemic to Peru which have been evaluated and classifi ed according to IUCN criteria (Beltrán et al. 2007). In the Department of Moquegua, 30 species have been recorded (Arakaki andCano 2003, Montesinos 2012). Th e species of Senecio described here were discovered in the tributaries of the upper Tambo River in southern Peru, an area of extraordinary species richness and a high level of endemism (Montesinos 2011(Montesinos , 2012. Senecio ser. Suff ruticosi Cabrera accounts for 143 species occurring on the American continent, especially in the Andes and Patagonia (Cabrera 1949, Cabrera 1985, Cabrera et al. 1999. Cabrera et al. (1999) divided S. ser. Suff ruticosi into fi ve subseries and described it as embracing suff ruticose or perennial herbs, glabrous or glandulose, with entire leaves which are dentate or, more rarely, incised, involucres discoid, and capitula isomorphic. Among those subseries, S. subser. Caespitosi Cabrera contains 50 species (Cabrera et al. 1999), of which thirteen occur in Peru at altitudes between 3500 m and 5000 m (Brako andZaruchi 1993, Beltrán et al. 2007): S. adenophyllus Meyen & Walp., S. algens Wedd., S. scorzonerifolius Meyen & Walp. and S. trifurcifolius Hieron. also distributed in northwestern Argentina, Bolivia and north of Chile, S. danai A. Gray and S. pucapampaensis Beltrán occurring only in central Peru (Beltrán 2007), S. evacoides Sch. Bip., S. expansus Wedd. and S. humillimus Sch. Bip. also distributed in northwestern Argentina and Bolivia, S. gamolepis Cabrera, endemic to central and southern Peru, S. rufescens DC. distributed from Colombia to northwestern Argentina, S. repens Stokes distributed from south Ecuador through Peru and northwestern Bolivia, and S. vegetus (Wedd.) Cabrera, also distributed in Bolivia. In S. subser. Caespitosi plants are characterized as suff ruticose (or herbaceous), glabrous or glandulose; leaves entire, dentate or, more rarely, incised; capitula discoid, medium or small; and fl owers isomorphic (Cabrera et al. 1999).
Notwithstanding the progress in taxonomical and molecular studies (Nordenstam 1977, Cabrera 1949, 1985, Cabrera et al. 1999, Pelser et al. 2007, Nordenstam et al. 2009), there are more species of the tribe Senecioneae occurring in the Andes which remain poorly understood and are awaiting discovery. Intergeneric relationships within Senecioneae are still largely unknown (Pelser et al. 2007); furthermore, the lack of knowledge about generic-level evolutionary relationships in Senecioneae remains the largest taxonomic problem on the way to obtaining a monophyletic delimitation of Senecio (Bremer 1994, Pelser et al. 2007. Phylogenetic positions for the members of S. subser. Caespitosi are still largely unknown, except for S. algens, S. humillimus and S. rufescens (Pelser et al. 2007), of which S. algens belongs to the Aetheolaena involucrata-A. patens clade and S. humillimus and S. rufescens to the Senecio glaber-S. donianus clade. Numerous new collections from Moquegua have been made in recent years (Montesinos 2011(Montesinos , 2012. A comparison with herbarium specimens, together with a review of the literature and taxonomic keys, has shown that these collections include three new species of S. subser. Caespitosi which are described below. Th ese new species were separated from the other species of this subseries on the basis of a set of characters such as habit, the presence or absence of trichomes, fl ower color, the number of phyllaries and involucral bracts, the involucre length and the achene type (Cabrera 1955, 1985, Cabrera et al. 1999. Th e new species can be found at elevations above 4500 m as terrestrial plants on bare rocky soils on the summits of high mountains in the north of Moquegua department, where they co-occur with several other acaulescent Senecioneae from S. subser. Caespitosi such as S. gamolepis, S. evacoides, and S. algens.
Ecology and distribution. 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.
Etymology. Th e specifi c epithet refers to Moquegua, where the only three collections are known from the north of the department.  Discussion. A comparison of the material has shown that S. moqueguensis is most similar to S. pucapampaensis and S. tassaensis sp. nov. Together with S. evacoides, S. expansus, S. repens and S. humillimus, it forms a coherent morphological and geographical group within S. 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 S. 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 S. evacoides, S. expansus and S. repens by the habit, density of trichomes, leaf shape and length, as well as by the calycular bracts and phyllary length and form.
Conservation status. Following the criteria and categories of IUCN (2001), a preliminary status of Critically Endangered (CR) is assigned. Th e 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). Th e suitable habitats for S. 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. Diagnosis. 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).
Description. 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. Synfl orescences of solitary, terminal capitula. Capitula  homogamous, discoid and pedicled (5-10 mm long). Involucres at fi rst 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, fi nely covered with trichomes, 1.5-2 mm long × 0.6-0.9 mm wide; carpopodium symmetrical in a shallow ring; pappus of smooth fi ne bristles, white, 4-6 mm long, with fi ne alternate single setulae. Discussion. Senecio sykorae appears to be closely related to S. gamolepis which grows at higher elevations but approaches the known range of S. sykorae within a few hundred metres. While S. 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, S. 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 S. gamolepis. Likely the leaves of S. sykorae are distinctive in that they are obovate-spathulate vs. linear-lanceolate. Also, the achenes in S. sykorae are larger (1.5-2 mm long) vs. 1-1.3 mm long in S. gamolepis. Senecio sykorae also diff ers from S. algens by the leaf and capitula length (shorter in S. sykorae), and from both species by the corolla colour (white vs. yellow). Less similarity is found in S. algens, S. humillimus, S. trifurcifolius, S. pucapampaensis and S. evacoides, and from which S. 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.
Ecology and distribution. 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. Etymology. Th is Senecio is named after the town of Tassa (Moquegua Region), downslope of Pirhuani peak where the species was found.
Discussion. Senecio tassaensis appears to be closely related to S. moqueguensis which grows at the same elevational range but approaches the known range of S. 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 S. moqueguensis. Senecio tassaensis is relatively a very rare species with an estimated 100 individuals known. It is less similar to S. pucapampaensis, S. evacoides, S. expansus and S. 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.
Conservation status. Following the criteria and categories of IUCN (2001), a preliminary status of Critically Endangered (CR) is assigned. Th e 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(iiii)); population estimated to number fewer than 100 individuals (D). Th e suitable habitats for S. 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.
Key to the species of Senecio ser. Suffruticosi subser. Caespitosi in Peru (adapted from Cabrera 1985, Cabrera et al. 1999