A taxonomic revision of the western South American genus Presliophytum (Loasaceae) Author Acuña, Rafael Universität Bonn, Nees-Institut für Biodiversität der Pflanzen, Meckenheimer Allee 170, 53115 Bonn, Germany. & Universidad de Costa Rica, Escuela de Biología, Apdo. Postal: 11501 - 2060 San Pedro de Mondes de Oca, Costa Rica Author Weigend, Maximilian Universität Bonn, Nees-Institut für Biodiversität der Pflanzen, Meckenheimer Allee 170, 53115 Bonn, Germany. text Phytotaxa 2017 2017-11-24 329 1 51 68 http://dx.doi.org/10.11646/phytotaxa.329.1.3 journal article 10.11646/phytotaxa.329.1.3 1179-3163 13721572 Presliophytum (Urb. & Gilg) Weigend (2006: 467) ≡ Loasa section Presliophytum Urb. & Gilg in Gilg (1894: 118) Type species : Presliophytum incanum (Graham) Weigend (2006: 467) ≡ Loasa incana Graham (1830: 169) . Erect 20–150 cm tall, densely branched herbs to shrubs (rarely poorly branched herbs < 10 cm tall) with stinging hairs. Scabrid hairs abundant on most surfaces, especially on abaxial leaf blade and outer ovary, glandular trichomes sometimes present on leaves and younger stems. Taproot present, usually thickened and fleshy, rarely thin and poorly branched. Leaves shallowly lobate, rarely toothed or sub-entire, mostly alternate (except lowermost pairs), petiole 3–100 mm , lamina 12–170 × 5–170 mm , ovate to reniform with crenate margin, rarely weakly toothed, base cuneate to deeply cordate, apices of lobes and blade, acute to rounded. Inflorescences complex dichasia, to ca. 100 cm long, symmetrical (in extra-Peruvian species) or asymmetrical (in shrubby Peruvian species); each flower erect or horizontal to deflexed in anthesis, with 2 foliose prophylls (flowers apparently irregularly alternating with foliage leaves, due to concaulescence and recaulescence) 3.0–60 × 1.0– 65 mm , similar to leaves in morphology but smaller and less disected; sepals five, 2.0–12 × 0.5–10 mm green, 3-veined, with entire margins; petals five, 4.0– 25 mm long, white (often slightly tinged green or cream) or yellow; nectar scales five, 2–7 mm long, white, yellow or greenish, usually unicolored, rarely bicolored white and yellow or green, with 3 dorsal threads 0.5–7.0 mm long, claviform (shorter than the nectar scale) or filiform (almost as long or longer than the nectar scale). Staminodes 2 per scale, 4–15 mm long. Stamens 30–130. Style 3–15 mm long, straight (twisting after fertilization), ovary inferior, placentae 3 to 5, rarely 2. Fruit a capsule, 5–15 × 3–12 mm , obconical or cylindrical to obovoid or subglobose, opening with 3–5 apical valves (rarely apparently indehiscent); seeds 0.5–4.0 mm × 0.2–1.5 mm , testa dark to tan brown, foveate-reticulate, or with 6–18 transversal constrictions. 2n = 12, 24 ( Grau 1988 , Weigend 2004). Five species from the xeric regions of western Peru , through northern Chile into western Argentina , frequent on rocky slopes. Etymology:— ‘ Plant of Presl’. Dedicated to the Czech botanist Carl Presl who made important contributions to the knowledge of Loasaceae in the 19th century. Similar taxa:— Due to its distribution in xeric regions, alternate phyllotaxis and star-shaped, pale corollas, Presliophytum could be confused superficially with the following Loasaceae taxa (characters of Presliophytum in parentheses). Both Huidobria have stinging trichomes absent (vs. present), nectar scales formed by four or more stamens (vs. always three, as indicated by the number of dorsal threads in each taxon) and seed testa either longitudinally striate or smooth to irregularly wrinkled (vs. foveate-reticulate or transversally constricted). Nasa Weigend (2006: 465) species with star-shaped, pale corollas have flowers pendent (vs. usually erect), dorsal threads on nectar scales absent (vs present), and seed testa reticulate (vs. foveate-reticulate or transversally constricted). Loasa series Floribundae Urb. & Gilg in Gilg (1894: 116 , 117) occasionally have alternate phyllotaxis, but have flowers pendent (vs. usually erect), nectar scales with red markings evident (vs. red absent), fruits semisuperior (vs. inferior) and seed testa deeply pitted (vs. foveate-reticulate or transversally constricted).