Senecio sangayensis D.L.A. Vásquez & J. Calvo, 2016

Vásquez, Diana L. A. & Calvo, Joel, 2016, Senecio sangayensis (Asteraceae, Senecioneae): a striking new species from the Ecuadorian highlands, Phytotaxa 268 (3), pp. 203-208 : 204-207

Senecio sangayensis D.L.A. Vásquez & J. Calvo , sp. nov. ( Fig. 1 & 2 )

Type:— ECUADOR. Chimborazo: near Atillo lakes, 02º13’51” S 78º32’43” W, 4061 m, 10 October 2010, D. L. A Vásquez 302 (holotype PRC, isotype MO).

Senecio sangayensis differs from all other Andean Senecio species in the combination of the following characters: robust habit, erect stem densely covered by coriaceous sessile leaves, striking racemiform synflorescence composed of dense cymose-corymbs subtended by triangular-ovate bracts, and semelparous life-history strategy.

Perennial semelparous plant up to 1.7 m (in bloom). Stem erect, unbranched, up to 5 cm in diam., and densely leaved with no internode elongation. Before developing the stem, basal leaves arranged in a rosette and covered with a mucilaginous fluid. When the stem starts developing, the basal and lower cauline leaves wither and remain attached to the stem. Leaves 13–35 cm long and 5–8 cm wide, coriaceous, elliptic-lanceolate, acute, sessile, slightly decurrent, denticulate, glabrescent above, densely arachnoid beneath especially when young. Synflorescence up to 50 cm long, 20 cm in diam., racemiform, composed of dense cymose-corymbs of ca. 6 capitula subtended by triangular-ovate bracts. Capitula radiate, ca. 5 cm in diam., becoming nodding as time passes. Involucre 10–13 mm in diam., 10–15 mm long, bell-shaped; involucral bracts 14–16, 10–12 mm long, 1.5–2.2 mm wide, without scarious margin, lanceolate, glabrous; supplementary bracts 10–14, 7–10 mm long, 1–1.2 mm wide, subulate, without scarious margin, almost as long as involucral bracts, glabrous. Ray florets 7–13, up to 25 mm long, yellow; disc florets 40–50, 6–10 mm long, yellow; style branches truncate. Achenes glabrous, 3–4.5 mm long; pappus whitish. Chromosome number: unknown.

Distribution, Habitat, and Ecology: — Senecio sangayensis is only known from three localities in the southern part of the Sangay National Park, which is located in the eastern Ecuadorian Cordillera ( Fig. 2B ). Two localities are situated around 3700 m a.s.l. on the west-oriented slopes of the Cordillera; one locality between the community of Pomacocho and the Ozogoche lakes, and the other between the community Pillcopata and the Culebrillas lake. The third locality is situated at 4061 m a.s.l. between the Ozogoche and Atillo lakes on the east-oriented slopes of the Cordillera. This side of the Cordillera, unlike the west-oriented slopes, is covered by forests that extend from the tree-line to the Amazonian forests ( Bader & Ruijten 2008).

The species occurs above the tree-line in a locally very humid páramo. The vegetation is dominated by Calamagrostis sp. and Neurolepis aristata . The species is semelparous, having only one reproductive episode during its life cycle.

Etymology: —The epithet sangayensis refers to the name of the National Park, “Sangay”, where the three localities known for the species were found. The National Park was named after one of its main features, the Sangay volcano.

Additional specimens examined (paratypes): — ECUADOR. Chimborazo: Alausí, Achupallas, páramo de Pomacocho, 02º20’ S 78º39’ W, 3655 m, 17 June 2013, J. Caranqui et al. 2306 (QCA-230005!, CHEP).

Discussion: —The racemiform synflorescence composed of dense cymose-corymbs subtended by triangular-ovate bracts, the coriaceous sessile leaves closely arranged along the stem, and the large radiate capitula make this species unique among the Andean Senecio species. Its robust habit (almost reaching 2 m tall) and the long-lived semelparous strategy are also unusual characters within Andean Senecio . Another robust species displaying large radiate yellow capitula is the Colombian endemic S. niveoaureus Cuatrecasas (1940: 6) . However, this species has a laxer synflorescence, paniculiform instead of racemiform, narrower leaves, and the whole plant is covered with a white lanate indumentum. Any confusion is very unlikely.

The singular morphology of S. sangayensis resembles that of Dendrosenecio keniensis ( Baker 1894: 140) Mabberley (1986: 100) from both the lower and upper alpine zone of Mount Kenya ( Kenya). The striking terminal racemiform synflorescence with large triangular-ovate bracts are pretty similar. The architecture of the capitulum is also similar, with a few subulate supplementary bracts almost as long as the involucral bracts and long yellow ray florets. The basal and lower cauline leaves of D. keniensis tend otherwise to be persistent at the flowering time, they are larger than in S. sangayensis and have a thick, whitish, lanate indumentum beneath. Unlike S. sangayensis , D. keniensis produces lateral branches near ground-level capable of rooting.

Another singular trait of S. sangayensis is that the young rosette secretes a mucilaginous substance as recorded in the Andean species Valeriana plantaginea Kunth in Humboldt et al. (1819: 329) and Oritrophium peruvianum ( Lamarck 1786: 316) Cuatrecasas (1961: 22) , and in some Afro-alpine giant rosette plants, i.e. Lobelia keniensis , Lobelia aberdarica , D. keniensis ( Young & Orden Robe 1986, Beck et al. 1982). This mucilage was suggested to act as a thermal buffer that protects plant organs from freezing temperatures. Thermal buffering requires the avoidance of intense supercooling. This is assured by the polysaccharide content of the mucilage that allows nucleation already upon slight supercooling ( Beck 1994). Further studies should be carried out to understand the significance and the role that this substance plays in S. sangayensis .

Conservation status: —This species is known from a restricted geographic area in the southern part of the Sangay National Park belonging to Chimborazo and Cañar Provinces ( Ecuador). The size of the populations varied from 5 to 100 individuals and consisted mainly of adult individuals (flowering and senescent). Several communities are found in their vicinity (e.g. Atillo, Ozogoche, Achupallas, Pillcopata). The páramo where the species occurs is used for cattle grazing and potato cultivation. Based on this, the species is assigned a preliminary conservation status of Endangered (EN) using the IUCN red list criteria ( IUCN 2001).

Figures

FIGURE 1. Senecio sangayensis. A. Radiate capitulum. B. Involucre. C. Part of the racemiform synflorescence and detail of the synflorescence bracts. D. Cauline leaves. E. Detail of young rosette leaves with mucilage. F. Rosette. A–D, F: plant photographed near laguna Culebrillas, Cañar (J. Calvo, not collected). E: plant from the type locality (D.L.A. Vásquez).

FIGURE 2. Senecio sangayensis. A. Habit. B. Distribution map (▲). C. Habitat. Population near laguna Culebrillas, Cañar (J. Calvo).