Presliophytum arequipense Weigend (2006: 467)

Acuña, Rafael & Weigend, Maximilian, 2017, A taxonomic revision of the western South American genus Presliophytum (Loasaceae), Phytotaxa 329 (1), pp. 51-68 : 58-60

1. Presliophytum arequipense Weigend (2006: 467) ( Figs. 1D , 2A, B , 3A)

Type: — PERU, Arequipa [Prov. Islay], Mollendo , ca. 30 m., on rocky cliff, 27 October 1937. D. Stafford 1017 (holotype: BM barcode BM000021454 !; isotype: F No. 1508586 [photo!]) .

Coarse, densely branched perennial shrub 50–100 cm tall. Stem epidermis with abundant glochidiate (sometimes obscured) and scabrid trichomes, scattered stinging and short-smooth trichomes. Taproot present, usually thickened and fleshy. Leaves lobate, opposite below, alternate above, petiole 4–20 mm, with glochidiate, scabrid and scattered stinging and short-smooth trichomes, lamina 20–60 × 15–45 mm, ovate with 3–7 lobes on each side, margin crenate, base cuneate to shallowly cordate, often asymmetric, blade and lobe apices obtuse to rounded, upperside with short-smooth, scabrid and sparse stinging trichomes (mostly on veins or blade margins). In older leaves, the trichome apices may fall, leaving behind basal cells, forming scale-like structures, underside densely covered in glochidiate and scabrid trichomes (rarely with glandular and stinging trichomes). Inflorescences densely frondose, complex asymmetrical dichasia, to ca. 50 cm long; each flower erect or horizontal in anthesis with two, sometimes sessile, prophylls (flowers apparently solitary and irregularly alternating with foliage leaves) 3–25 × 5–25 mm, similar to vegetative leaves in morphology and indumentum, but often narrower and weakly lobate; pedicels with glochidiate (sometimes obscured), scabrid, short-smooth and stinging trichomes. Sepals five, broadly ovate, 5–12 × 5–10 mm green, 3-veined with entire margins, almost as long as the petals, indumentum of each surface similar to that of the respective leaf surface; petals five, full to half spreading, cymbiform, 5–9 mm long, cream to greenish-white, tinged darker greenish on the abaxial surface, with scabrid, glochidiate and scattered, weak, stinging trichomes, margins flat or slightly revolute, finely serrate and clearly distinguishable form the petal central depression; nectar scales five, 2–5 mm long, cream to greenish-white (not contrasting with petal color), unicolored, concave, slightly bulging, with a poorly developed papillae-margined neck and rudimentary apical wings. Filiform dorsal threads, three, 1.5–3(–5) mm long, the central sometimes shorter than the laterals, attached subapically to the scale. Staminodes 2 per scale, 4–10 mm long, the distal 2/3rds filiform, glabrous, the proximal third abruptly expanded, with a flange towards the nectar scale, margins papillose. Stamens 50–75, filaments 5 mm long. Style 5 mm long, straight, twisting after fertilization, ovary inferior, with a densely pubescent roof covered in short-smooth and scabrid trichomes, outer wall with abundant glochidiate and stinging trichomes, sometimes with scabrid and short-smooth trichomes, placentae 3–5. Fruit a capsule 6–9 mm diameter, subglobose, opening with 3–5 apical valves; seeds ca. 1200–3000 per capsule, 0.5 mm × 0.2–0.5 mm, testa dark brown, foveate-reticulate. Seed testa cells polygonal.

Notes:— Although this species was collected for the first time early in the 19th century by D’Orbigny, it was not recognized as a distinct taxon until 1997 (Weigend 2006). Its most distinctive traits are the size, proportions and morphology of the perianth parts, which are markedly different from its close relative Presliophytum incanum ( Acuña et al. 2017) .

Etymology:— The epithet alludes Arequipa, the Peruvian department to which this species is endemic.

Illustrations:— Floral scale morphology: Urban & Gilg (1900: Tab. VII. Fig. 11).

Distribution:— Endemic to southern Peru. So far known from only three localities very close to each other near the coast, at elevations below 100 m in Distrito de Mollendo, Provincia de Islay, Departamento de Arequipa ( Fig. 4 ).

Phenology:— The few known wild collections flowered in October. In cultivation, the plants flower throughout the year.

Ecology:— This plant grows on cliffs, scree slopes and dry river beds and in the Lomas near Mollendo, sometimes sympatrically with cacti. No information about pollinators has been obtained for this species.

Conservation status:— Although not analyzed by Rodríguez & Weigend (2006) this species is known from only two recent collections, both from essentially the same place, which is currently under urban development. Due to its rarity, limited range, and human pressure, we recommend this species to be considered as critically endangered (CR) according to criteria A4bc, B2ab(i,ii,iii,iv,v). Several attempts to find the plant in the wild were unsuccessful and it may be extinct in the wild.

Additional specimens examined:— PERU. Arequipa: Prov. Islay, Islay near Arequipa, 1833(?), D’Orbigny s.n. ( P: P00123875 ) ; Antigua trocha desde playa Catarindo hasta la Carretera Panamericana, 32 m, 8 October 2004, Ortiz et al. 116 ( BONN, HUSA) ; ditto, 42 m, 8 October 2004, Ortiz et al. 121 ( BONN, HUSA) .

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 2. Microstructure and trichome morphology of Presliophytum. A. Adaxial foliar surface of a mature leaf of Presliophytum arequipense (Ortiz et al. 121, BONN). Presliophytum incanum has virtually identical indumentum. B. Abaxial foliar surface of a mature leaf of Presliophytum arequipense (Ortiz et al. 121, BONN). Presliophytum incanum may have similar indumentum or mostly made up by scabrid trichomes. C. Adaxial foliar surface of a mature leaf of Presliophytum heucheraefolium (Weigend et al. 7691C, BONN). This species and Presliophytum sessiliflorum have abundant and relatively long uniseriate glandular hairs, on leaves and younger stems. Presliophytum malesherbioides has similar but much shorter trichomes in some areas of the stem. D. Abaxial foliar surface of a mature leaf of Presliophytum heucheraefolium (Weigend et al. 7691C, BONN). GL: Glochidiate trichome, GT: Uniseriate glandular trichome, SC: Scabrid trichome, SS: Short smooth trichome. Scale bars A, B: 100 μm; C, D 200 μm.

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.