Alchornea acroneura Pax & Hoffmann (1914: 229)

Murillo-Aldana, José, 2018, Novelties in the genus Alchornea (Euphorbiaceae), Phytotaxa 375 (3), pp. 203-213 : 204-205

Alchornea acroneura Pax & Hoffmann (1914: 229) ( Fig. 1 )

Type:— PERU. San Martín: Cerros al este de Moyobamba, 1500–1600 m, n.d. A. Weberbauer 4752 (lectotype MOL!, staminate branch, designated here, isolectotype: G!).

Tree to 6 m high, abundantly covered with small rotate-stellate trichomes <0.1 mm in diam. Leaves alternate, stipules triangular, ca. 0.5 mm long; petiole 0.3–1.5(–2.0) cm long, terete, glabrous; blade elliptical, (3.5–)5–14 × 1.6–5.0 cm, apex retuse to acuminate, acumen 0.5–2.0 cm long, margin serrate with glandular teeth, base acute to obtuse; both surfaces sometimes glabrescent, glandular spots occasionally present in the axils of the tertiary veins on the lower surface; domatia generally present, as either pockets enclosing hair-tufts, or sometimes just hair-tufts, the trichomes simple to multiangular stellate, <0.3 mm in length; venation acrodromous, generally suprabasal, perfect, secondary veins in 1(–2) pairs, tertiary venation perpendicular to the midvein; midvein elevated on the upper surface, veins prominent on the lower surface. Inflorescence unbranched, axillary, solitary. Staminate inflorescence 4–11(–14) cm long, peduncle 0.3–1.2 cm long, <0.1 cm in diam.; axis ca. 0.5 mm in diam., moderately covered with stellate trichomes, rotate and multiangular, ca. 0.1 mm in diam.; flowers in clusters of up to 8 per node, internode <7 mm long; bracts of groups widely ovate, 1.0 × 0.8 mm, abundantly covered with rotate-stellate trichomes, usually with a spherical dorsal gland; pedicels <1 mm long, buds 0.8–1.2 mm wide, with a few apical trichomes; sepals 2, partly fused, lobes acute; stamens (7–)8, connate at the base, glabrous, anthers ca. 0.8 mm long, sometimes apiculate. Pistillate inflorescence 5–6 cm long, peduncle <0.6 cm long, bracts ovate, 2 mm long, with a dorsal gland; flowers solitary, pedicels (2–)3–6 (–10) mm long; sepals 3–4, free, 1.0– 1.5 mm long, sparsely covered with rotate-stellate trichomes toward the apex, ovary ca. 2 × 2 mm, densely covered with rotate-stellate trichomes, 2–locular; styles 2, 0.7–1 cm long, filiform or foliose, connate at the base, sparsely covered with rotate-stellate trichomes on the dorsal surface, smooth-to-slightly rugose internally, apex entire. Young fruit bilobed, glabrescent, green, styles persistent, seed not seen.

Distribution: —Located in the Andes, from southern Colombia to Peru, at elevations between 950 and 1800 m.

Phenology: —Staminate flowers have been found in May, August and September, pistillate flowers and fruits in February.

Notes: — Alchornea acroneura was proposed by Pax & Hoffman (1914: 229), who characterized the species by leaves with acrodromous venation and lacking additional secondary veins. Macbride (1951) considered A. acroneura as a separate species, but this author mentioned that Williams (1936: 268) included A. acroneura under A. triplinervia ; however, that author did not cite this species in the cited publication. More recently, Govaerts (2000) considered them as good species too, but Secco (2004) supported the synonymy. Both species are similar by their perfect acrodromous venation and the type of inflorescence, i.e., axillary racemes. However, the venation is very characteristic of A. acroneura , with only 1(–2) pairs of secondary veins, the basal pair approaching the apex, whereas A. triplinervia has 3–4(–5) pairs, the basal pair generally reaching at least 2/3 of the distance to the apex of the blade. In addition, in A. triplinervia the both inflorescences more or less in fascicles, and the pedicels of the pistillate flowers are shorter (0.5–1.0 mm vs. 2.0–6.0 mm) and sepals are connate (vs. free).

The original description of A. acroneura was based on Weberbauer 4752 (Pax & Hoffman 1914). This collection was found in two herbaria, one of them at G, and the other one at MOL. The duplicate at G does not have reproductive structures, but the one at MOL has a staminate and a pistillate branch, probably from two individuals. The staminate branch has leaves and more abundant flowers, for this reason it is selected as lectotype.

Additional specimens examined:— COLOMBIA. Cauca: Tambo, PNN Munchique, Serranía de La Paz , sector El Rosal , camino de Popayán a López de Micay , cerca al alto de La Paz, 2º02´W, 76º56.118´W, 2050 m, 26 September 2016 (ster), J. Sánchez 2099 ( COL). Nariño: Ricaurte, Reserva Natural La Planada a km 7 de Chucunés, 13 February 1992 (fl, fr), R. Giraldo 105 ( COL, HUA), 134 ( HUA) . ECUADOR. Morona-Santiago: Limón Indanza, Cordillera del Condor, Centro Shuar Yunkumas. Cerro Chunak Naint, 14 September 2005 (fl), 1000–1270 m, D. Neill 14820 ( COL, MO). Zamora-Chinchipe: Nangaritza, cordillera del Cóndor, west side of upper Río Nangaritza , along road about 13 km south of Guayzimi , silica mine La Daniela, 18 September 2007 (fl), D. Neill 15839 ( COL, MO) ; Nangaritza, cordillera del Cóndor ; cuenca alta del Río Nangaritza, centro Shuar Shaime, por la unión de los Ríos Nangaritza y Numpatakaime , cerca de la cueva de Los Tayos , 25 August 2002 (fl), W. Quizhpe 242 ( COL, MO) ; Cordillera del Cóndor, Cantón El Pangui, Parroquia Tundayme, arriba del valle del Río Quimi , 30 sep 2006 (fl), W. Quizhpe 2387 ( COL, LOJA, MO) ; Yacuambi, Cordillera Oriental de los Andes, Parroquia La Paz, Centro Shuar Washikiat , Reserva Micha Nunka , 7 May 2007 (fl), 1130 m, A. Wisum 1051 ( COL, MO) .

Figures

FIGURE. 1. Alchornea acroneura Pax & K.Hoffm. A. Staminate branch (R. Giraldo 105, COL). B. Pistillate branch (W. Quizhpe 2387, COL). C. Pistillate flower (R. Giraldo 105, COL).