Arenaria acaulis Montesinos & Kool, 2015

Montesinos-Tubée, Daniel B. & Kool, Anneleen, 2015, Arenaria acaulis (Caryophyllaceae), a new species from South Peru, Phytotaxa 220 (1), pp. 77-82 : 78-80

Arenaria acaulis Montesinos & Kool , sp. nov. ( Figs. 1–2 )

Type: — PERU. Moquegua Region: General Sánchez Cerro Province, Ubinas District: Larsepesca site, terrestrial on clayey rocky soils on the plateau peaks between Coalaque and Tassa towns, 4653 m, 16°08’32’’S, 70°43’08’’W. 4 April 2009, Montesinos 2475 A (holotype USM!, isotypes MO –2219338!, HUPCH –4221). Image of the isotype at MO available at http://tropicos.org/Specimen/100196348

Diagnosis:— The new species is morphologically similar to Arenaria boliviana but is clearly distinguished by the shorter stem length, ciliate (not glabrous) short branches; ovate rather than oblong-lanceolate leaves always covered with dense, long trichomes, never glabrous; pedicels shorter than or equal to the size of the calyx (not twice as long), sepals broadly ovate (not ovate-oblong) and covered with trichomes as opposed to usually glabrous, as well as by the presence of petals.

Description:— Perennial herb, deep rooted, pulvinate, forming solitary tufts 0.8–1.2 cm tall and 4–6 cm in diameter. Stems 5–10 mm long, often densely branched and covered by older leaves in the central and lower parts; internodes short, less than 0.2 mm in length. Leaves opposite, imbricate, gradually reduced in length and width upward on stem, the largest near the central portion and base; lamina ovate, 1.2–1.9 mm × 0.8–1.2 mm, densely covered by thin trichomes (about 0.1–0.4 mm long) on the margins except in the surfaces and the base; base truncated and apex acute; leaves light green with greenish round dots near the pale red midrib, margins also pale red. Flowers solitary, with short pedicels of about 0.2–0.5 mm long and covered with short, fine trichomes. Calyx cylindrical to narrowly campanulate, the 5 sepals mostly 0.8–1.2 mm long, ovate, apically obtuse or rounded, light green and inconspicuously 1-veined, with densely scarious margins. Corolla tubular in early anthesis, becoming narrowly campanulate, the petals shorter than the sepals, ca. 1.2 mm long, the blades broadly ovate, glabrous, apically rounded or obtuse, pale white-greenish, with an inconspicuous midrib. Stamens usually 10, spreading-ascending, the filaments linear (ca. 0.8–1.2 mm long), white, the anthers elliptical, pale-yellow and reniform (ca. 0.2 mm long). Ovary ovoid, ca. 0.7 mm long, pale yellowwhite; styles 3, at anthesis 1–1.5 mm long, erect or slightly spreading, the curved, minute, scarious stigmas ca. 0.35 mm long. Capsule broadly ovoid, enclosed by the persisting calyx and petals, 1.7–2 mm long and somewhat incurved; seeds 10–16, rounded, 0.4–0.6 mm in length, rounded to some extent elliptic, surface reddish-brown, shiny, and rarely granulate.

Etymology:— The epithet acaulis refers to the tufted and acaulescent habit of the species.

Ecology and distribution:— Arenaria acaulis is distributed on highland plateaus of the Moquegua Region (South Peru). It grows on rocky slopes at an elevation of 4450–4700 m.a.s.l. Associated species are: Astragalus peruvianus Vogel (1843: 18) , Azorella compacta Phil. (1891: 28) , Mniodes pulvinata Cuatrec. (1954: 5) , Pycnophyllum molle J. Remy (1846: 355) , and the endemics: Nototriche digitulifolia A.W. Hill (1948: 127) , Senecio moqueguensis Montesinos (2014: 3–6) and Senecio sykorae Montesinos (2014: 6–11) . Flowering and fruiting between March and April.

Taxonomical notes:— The new species is unique among the Neotropical Arenaria because of its dense cover of trichomes and the tufted, cushion–like habit. A. acaulis most closely resembles A. boliviana ( Williams 1898: 425) MacBbride (1936: 597–598) . It differs by its shorter stem and internode length, the short branches being ciliate; the leaves ovate and densely covered by long trichomes; pedicels shorter or equal to the size of the calyx, sepals broadly ovate and densely covered with trichomes, and by the presence of petals.

The new species is further differentiated from A. dicranoides Kunth (1823: 34) by the habit, plant size, height and leaf shape, where in A. acaulis leaves are smaller and have a smooth tip, not coriaceous. A. nitida ( Bartling 1831: 12) Rohrbach (1872: 249) differs in its leaves being larger and bisulcate and also by the glabrous sepals.

Conservation status:— On the basis of the IUCN criteria and categories ( IUCN 2014), a status of Critically Endangered (CR) is assessed. The total area of occupancy (AOO) is less than 10 km ² (ca. 5 km ²) (criterion B2), only one population is known, despite extensive fieldwork in the area by the first author (B2a), habitat inferred to be continuing to decline [B2b(i–v)), population estimated to number fewer than 150 individuals (criterion D). The suitable habitats for A. acaulis 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.

Additional material examined (paratypes):— PERU. Moquegua Region, General Sánchez Cerro Province, Ubinas District, terrestrial on highland rocky slopes near Larsepesca , Coalaque town , 4677 m, 16°08 ʹ 19 ʹʹ S, 70°43 ʹ 15 ʹʹ W, 21 March 2009, Montesinos 2475 B ( USM, MO –2274701) ; Moquegua Region, General Sánchez Cerro Province, Ubinas District, terrestrial on clayey rocky soils on the Querala plateaus, 4618 m, 16°07 ʹ 12 ʹʹ S, 70°50 ʹ 09 ʹʹ W, 24 March 2013, Montesinos 4026 ( USM, HSP) ; Moquegua Region, General Sánchez Cerro Province, Ubinas District , terrestrial on rocky slopes close to the road between Matazo and Querala, 4584 m, 16°10 ʹ 02 ʹʹ S, 70°43 ʹ 15 ʹʹ W, 28 March 2015, Montesinos 4241 ( USM, HSP, HUT) .

Figures

FIGURE 1. A. Habitus: complete plant (X 8) B. Branch with flower (X 30) C. Leaf, outside (X 50) D. Leaf, inside (X 50) E. Flower (X 50) F. Flower, opened (X 50) G. Ovary (X 50) H. Sepal, inside (X 50) I. Sepal, outside (X 50) J. Petal, inside (X 50) K. Petal (other), inside (X 50) L. Opened flower = very young fruit (X 40) M. Fruit, 1 sepal and 1 petal removed (X 40) N. Seed (X 65). Drawing by H. de Vries.

FIGURE 2. Habit of Arenaria acaulis (along road between Matazo and Querala, Ubinas district, at 4584 m).