Presliophytum sessiliflorum (Phil.) R.H. Acuña & Weigend

Acuña, Rafael & Weigend, Maximilian, 2017, A taxonomic revision of the western South American genus Presliophytum (Loasaceae), Phytotaxa 329 (1), pp. 51-68 : 65-66

5. Presliophytum sessiliflorum (Phil.) R.H. Acuña & Weigend in Acuña et al. (2017: 373) ( Figs. 1B , 3F, L)

≡ Loasa sessiliflora Philippi (1893:12)

Type:— [ CHILE, Antofagasta, Prov. Antofagasta] Sierra Esmeralda, Des Atacama, 20 October 1883, [ F.] S [an] Roman s.n. (holotype: SGO barcode SGO 000003420 [photo!]).

Densely branched subshrub to ca. 50 cm tall. Stem epidermis green, with abundant glochidiate, scabrid and stinging trichomes, glandular trichomes in younger parts. Taproot perennial, fleshy and thick. Leaves opposite below, alternate above, petioles to 20 mm long in basal leaves, similar to the stem in trichome cover, but with more glandular trichomes especially near the leaf blade, terminal leaves mostly (sub)sessile, lamina 20–60 × 7–35 mm, ovate with 3–8 triangular lobes on each side, margin toothed, base truncate, sometimes slightly asymmetrical, blade and lobe apices acute, adaxially with numerous scabrid, short smooth, glandular and stinging trichomes, rarely with few glochidiate trichomes, abaxially with abundant glochidiate trichomes, stinging trichomes restricted to the larger veins. Inflorescences frondose dichasia, to 10 cm long, the trichome cover similar to the stem, but with more glandular trichomes; flowers horizontal to deflexed in anthesis, with two, sessile prophylls per flower (flowers apparently irregularly alternating with the prophylls), 3–17 × 2–10 mm, diminishing in size towards the terminal portions of the inflorescence, similar to vegetative leaves in trichome cover but usually only slightly serrate to dentate with 3–4 teeth per side, flowers subsessile or with pedicels, shorter than the petals, to 4(–6) mm, with glochidiate, glandular and stinging trichomes. Sepals five, broadly lanceolate to ovate, 2.5–5 × 2.5–4 mm, <1.25 × as long as wide, green, 3-veined, margins entire, indumentum of each surface similar to that of the respective leaf surface but with less glandular trichomes; petals five, full spreading, cymbiform, 7–14 mm long, white or very light greyish, tinged greenish on the abaxial surface with abundant scabrid, glochidiate, glandular and rarely weak stinging trichomes adaxially, margins slightly undulate; nectar scales five, 3–4 mm long, white (not contrasting with petal color), concave, slightly bulging, apex weakly bilobate, neck with a weak rim, rudimentary apical wings. Dorsal threads, three, filiform, of about the same length, to ca. 3 mm long, attached to the tip of the scale. Staminodes 2 per scale, to ca. 10 mm long, S-shaped, the distal 2/3rds filiform and glabrous, the proximal third abruptly thickened, flattened and papillose. Stamens 30–50, filaments 5–10 mm long. Style 10 mm long, straight, but twisting after fertilization, persistent in fruit, the basal portion with scabrid trichomes; ovary inferior, with a densely pubescent roof with scabrid trichomes, outer wall with abundant scabrid and stinging trichomes, placentae 2. Fruit a 2 locule capsule 5–6 × 3 mm (not counting the persistent sepals), obovoid, apprently indehiscent; seeds (3–)4(–6), two per locule, 3–4 mm × 1 mm, narrowly ovoid, testa tan brown, darker towards hilar end, with 12–18 transversal constrictions. Seed testa cells tetragonal, periclinal walls with undulate sculpturing.

Notes:— The name Loasa longiseta has been often misapplied to this species ( Weigend et al. 2008). Urban & Gilg (1900) knew about this species and considered it possibly related to Loasa longiseta , but they were unable to examine the only specimen known at the time (the holotype). Its taxonomic status has been clarified only recently ( Acuña et al. 2017). The dimerous gynoecia and two-seeded locules observed in this species are rare in the tribe Loaseae .

Etymology:— The epithet refers to the short-pedicellate to subsessile flowers of this species.

Illustrations:— Inflorescence architecture: Weigend et al. (2004b: Fig.6A incorrectly called “ Loasa longiseta ”). Floral diagram: Grau (1997: Ab. 3).

Distribution:— Endemic to Chile. Presliophytum sessiliflorum grows only in scattered localities in coastal mountain ranges of the Región de Antofagasta and possibly northernmost Región de Atacama, Chile, at elevations under 1000 masl, and less than 20 km inland from the Pacific Ocean ( Fig. 4 ).

Phenology:— Known to flower between October and April.

Ecology:— This plant seems to be restricted to habitats with oceanic influence. The capsules are apparently indehiscent and thus the fruit and the seeds are expected to be dispersed as a single unit.

Conservation status:— It has been reported by Johnston (1929) and by Jiles, in a specimen label, that this species could be common locally [Jiles 5343 (CONC)], and may occur in disturbed habitats, e.g., La Chimba NE of Antofagasta [(Luebert et al. 3405 (BONN)]. Marticorena et al. (1998) recorded this species for Región de Antofagasta, but its conservation status was not analyzed. Due to our rudimentary knowledge of its abundance and distribution we consider Presliophytum sessiliflorum as DD.

Additional specimens examined:— CHILE. Antofagasta: Prov. Tocopilla , La Carmelita, 750 m, 8 November 1969 ; Jiles 5343 ( CONC) ; Prov. Antofagasta: Quebrada La Chimba , 340 m, 18 October 2016, Luebert et al. 3405 ( BONN) ; bare rocky canyon, 200 m, 3 April 1925, Pennell 13026 ( F) ; Quebrada de Botija , al norte de Paposo, 400 m, 29 November 1988, Hoffmann 187 ( CONC) ; Sierra Esmeralda, along trail between Posada de los Hidalgos and Quebrada Cachina via Portezuelo de Mina Carola. 1.5 Km N, 14 December 1925, Johnston 5674 ( F) .

Figures

FIGURE 1. Vegetative morphology of Presliophytum.A. Habit andhabitat of shrubby Presliophytum incanum (Quinistaquillas, Moquegua, Peru, not vouchered). The three species of Peruvian Presliophytum have similar habits. B. Habit and habitat of subshrubby Presliophytum sessiliflorum (Quebrada La Chimba,Antofagasta, Chile, Luebert et al. 3405, BONN; photo courtesy of F. Luebert).C. Habit and habitat of herbaceous Presliophytum malesherbioides (Juntas del Toro, Coquimbo, Chile, not vouchered; photo courtesy of M. Eyzaguirre). Mature specimens of this species range from unbranched annuals to densely branched subperennial herbs as the one illustrated. D. Mature leaf of Presliophytum arequipense (cultivated, seeds collected near Mollendo, Arequipa, Peru, Ortiz et al. 121, BONN). E. Mature leaf of Presliophytum heucheraefolium, (cultivated, seeds collected near Río Cacchán, Áncash, Peru, Weigend et al. 7691C, BONN). F. Mature leaf of Presliophytum incanum (cultivated, seeds collected near Ullpan, Áncash, Peru, Weigend & Hilger 8912C, BONN). G. Mature leaf of Presliophytum incanum (cultivated, seeds collected near Omate, Moquegua, Peru, Ackermann & Cáceres 674, BONN). Scale bars 15 mm. Photos by R.Acuña and M. Weigend, unless otherwise credited.

FIGURE 4. Natural distribution of Presliophytum based on herbarium specimens. P. incanum W = Presliophytum incanum with white or indeterminate color corollas. P. incanum Y = Presliophytum incanum with yellow corollas.