Miconia rheophytica Posada

Posada-Herrera, Juan Mauricio & Almeda, Frank, 2018, Miconia rheophytica (Melastomataceae: Miconieae), a new and endangered species from the Magdalena Medio region of Colombia, Phytotaxa 371 (1), pp. 55-61 : 56-60

Miconia rheophytica Posada ‒ Herrera & Almeda, sp. nov. ( Figs. 1 & 2)

Type:— COLOMBIA. Antioquia: Municipio de San Luis, río Samaná Norte, 2 km abajo del puente de la carretera Medellín ‒ Bogotá. 6° 0’ 59.19’’N, 75° 55’ 51.04’’W, 430 m, 18 diciembre 2016 (fl, fr), S. E. Hoyos-Gómez 3105 (holotype: HUA!). Figs. 1, 2.

Diagnosis: Unusual and unique among species of the Octopleura clade in being rheophytic and in having a combination of narrowly elliptic to ovate-lanceolate leaf blades with entire to subentire margins that have evenly spaced spreading smooth eglandular trichomes 0.8 − 1.4 mm long, unribbed hypanthia covered with a mixture of basally roughened trichomes and dendritic trichomes with short axes, anthers with two ± truncate apical pores, eglandular anther appendages, 3-locular ovary, and berries that are bright blue at maturity.

Shrub 0.6–1.5 m tall with open and lax branching. Distal internodes rounded-quadrate, nodal line absent. Indumentum on distal internodes, adaxial surfaces of petioles, and primary and secondary elevated veins on abaxial foliar surfaces consisting of a moderate to dense cover of brown dendritic trichomes with short axes and terete radiating arms. Leaves of a pair somewhat anisophyllous; petioles 0.3 − 1.8 cm long, deeply canaliculate adaxially but this is often obscured by indumentum; blades 5.2 − 9.4 × 1 − 1.8 cm, narrowly elliptic to ovate-lanceolate, the base rounded to obtuse, the apex acuminate to attenuate, the margin essentially entire or vaguely subentire with evenly spaced spreading smooth eglandular trichomes 0.8 − 1.4 mm long, papyraceous when dry; adaxial surface of mature blade glabrous, abaxial surface essentially glabrous but commonly with dendritic trichomes with short axes persisting to varying degrees along contact points of primary and secondary veins with blade surface and at the point where these veins diverge from one another at the blade base, 3 − 5-plinerved including the tenuous marginal veins with the innermost pair of secondary veins diverging from the midvein above the blade base. Inflorescences axillary in short dichasia 0.6 − 1 cm long with 2 − 3 flowers or dichasia sessile to subsessile in leaf axils; bracts and bracteoles 0.5 − 0.7 × 0.2 − 0.3 mm, triangular-subulate, light green or pale red, glabrous, persistent in fruit. Flowers 5-merous on pedicels 3.4 − 4.3 mm long with dendritic trichomes like those on the petioles and distal internodes but less dense. Hypanthia 3 − 3.4 × 1.4 − 1.7 mm, campanulate and unribbed but somewhat constricted and tapered distally below the torus into a neck-like distension 1.8 − 2 mm long, densely covered with a mixture of reddish-purple elongate somewhat spreading trichomes 0.3 − 0.5 mm long with roughened bases and dendritic trichomes with short axes. Calyx open in bud and persistent in fruit, greenish-yellow, adaxially glabrous, abaxially nearly glabrous or with indumentum like the hypanthium but much sparser, lobes 1.2 − 1.3 mm, depressed-triangular, the margin entire, the apex bluntly acute; exterior calyx teeth 1.4 × 1.3 mm, bluntly conic-triangular and tipped with a smooth trichome that slightly exceeds the lobes. Petals 1.2 − 1.3 × 1.6 − 1.8 mm, obovate, the margin entire, the apex rounded-truncate, white, densely papillose on both surfaces, reflexed at anthesis. Stamens 10, isomorphic, erect and closely encircling the style at anthesis; filaments 1.6 − 1.8 × 1.2 mm, white but yellow distally, glabrous; anther thecae 1.5 × 0.5 mm, linear-oblong, opening by two ± truncate apical pores, yellow; connective yellow, prolonged dorso-basally into a blunt deflexed eglandular appendage 0.3 mm long. Ovary 3 × 3 mm long at anthesis, 3-locular with axile placentation, completely inferior; style 5.3 mm long, 0.7 mm wide at the middle, terete and tapering to 0.5 mm distally, white, glabrous; stigma rounded-truncate, 0.66 mm wide and somewhat expanded when receptive. Berries with enveloping hypanthia 3.4 − 4.2 × 3.4 − 5 mm, ± globose to subglobose, reddish-purple when immature turning bright indigo blue when mature, the indumentum of mature hypanthia persistent but scattered and inconspicuous. Seeds 0.75 − 0.77 × 0.4 − 0.45 mm, ovoid, lateral and antiraphal symmetrical planes elliptic to elliptic-ovate, the highest point toward the chalazal side; raphal zone oblong, extending the entire length of the seed and expanded along its entire length on all sides into a well-developed skirt-like angled appendage that exceeds the corpus of the seed and collapses when dry.

Phenology:—This species has been collected in flower in March, June, July, November, and December; fruiting material has been collected in March, June, July, September, November, and December. It seems possible that it may flower and fruit most months of the year.

Distribution and habitat:— Miconia rheophytica appears to be largely restricted to the Magdalena Medio region of Colombia where it is known only from the Department of Antioquia ( Fig. 3). It grows along rocky banks of Río Nechí, and in the Río Samaná Norte and Río Claro river canyons in the municipalities of Anorí and San Luis at elevations of 110 − 600 m.

Conservation status:—This species is known to us from the type and eight other collections. The type and one of the paratypes were recently collected in the river canyon of Samaná Norte. Two collections were made in the municipio of Anorí and the other four come from the river canyon of Río Claro. Collections from Río Claro may be afforded some protection in Reserva Natural Cañón de Río Claro, a private conservation area covering some 500 hectares. The other collections come from areas that have no official protected status. The Samaná Norte river canyon is the type locality of Miconia rheophytica . This region has recently attracted the attention of scientists and conservationists. The rheophytic plants that grow along this river are under threat because a dam for a hydroelectric plant is planned to flood a large tract of the Samaná Norte river. Plans for this dam are already in progress and a license has been granted to the interested firm by the Colombian Environmental Licensing Agency (ANLA) based on an environmental impact study ( Hoyos-Gómez & Bernal 2018). The EOO is 12,900 km ² and the AOO is 16 km ². Because of its limited AOO, fragmented population structure in isolated river canyons, and the threat that rheophytic plants in these canyons face from massive flooding for dam construction, we recommend a conservation classification of Endangered (EN): B2ab(iii).

Discussion: — Miconia rheophytica is readily distinguished from all other members of the Octopleura clade by its rheophytic habitat preference, narrowly elliptic to ovate-lanceolate leaf blades with entire to subentire margins that have evenly spaced spreading smooth eglandular trichomes 0.8 − 1.4 mm long, indumentum of dendritic trichomes with short axes and terete radiating arms on distal internodes, adaxial petiole surfaces, and primary and secondary veins on abaxial leaf surfaces, unribbed hypanthia that are constricted and tapered distally below the torus and covered with a mixture of basally roughened trichomes and dendritic trichomes with short axes, eglandular anther appendages, 3- locular ovary, and berries that are bright blue at maturity. By virtue of having moderately anisophyllous leaf blades at each node, papillose petals, and seeds with raphal margins that are expanded on all sides into well-developed fleshy appendages, M. rheophytica can confidently be assigned to the Quinquenervia subclade within the Octopleura clade ( Gamba & Almeda 2014). Of the seven species presently included in this subclade, M. rheophytica appears to be closest to M. atropurpurea Gamba & Almeda (2014: 57) , M. neocoronata Gamba & Almeda (2014: 95) , and M. reitziana (Cogn. & Gleason ex Gleason 1939: 115) Gamba & Almeda (2014: 117) . All three of these species differ consistently from M. rheophytica in having anthers with one dorsally inclined apical pore, 5-locular ovaries, and bluntly 10-ribbed hypanthia.

Among these three close relatives, only M. atropurpurea has mature berries that are bright blue like M. rheophytica but it otherwise differs consistently in having elliptic to elliptic-ovate leaves that are wider (5 − 7 cm) and typically flushed red-purple abaxially, and hypanthia with persistent spreading smooth trichomes 1–1.3 mm long. Both M. neocoronata and M. reitziana differ from M. rheophytica in having berries that are blue-black at maturity. The former has ovate to elliptic-ovate leaves that are also wider (5 − 9.5 cm). The latter also has ovate to elliptic-ovate leaves that are much wider (7.8 − 11 cm) and its hypanthia are covered with spreading persistent elongate smooth trichomes 0.9 − 1.2 mm long that are intermixed with resinous slightly furrowed more or less stalked glands ca. 0.05 mm long. For additional descriptive and distributional information for these species see Gamba & Almeda (2014).

Etymology:—The specific epithet is derived from the word rheophyte, a plant that grows along margins of fast moving river currents with frequent flooding. This is an environment that is particularly harsh for many organisms.

Additional specimens examined: — COLOMBIA. Antioquia: Municipio de San Luis, Cañón del Río Claro , sector sur-oriental 5° 53’ N, 74° 39’ W, 350 ‒ 400 m, 30 marzo 1984 (fl, fr), A. Cogollo 1499 ( HUA!, JAUM!) ; Municipio de San Luis , 600 m, 12 septiembre 1982 (fr), E. Rentería & A. Cogollo 2628 ( JAUM!) ; Municipio de Anorí, vía Dos Bocas- Providencia , de Toná-Liberia a lo largo del río Nechí 7° 28 N, 74° 56’ W, 110 − 280 m, 11 julio 1987 (fl), R. Callejas, J. Betancur & F. J. Roldán 4538 ( HUA!) ; Municipio de San Luis, Cañón del Río Claro, 5° 49’ 59.76’’ N, 74° 52’ 00.04’’W, 435 m, 4 noviembre 2006 (fl, fr), H. David, F. Giraldo, A. Patiño & Estudiantes de Ecología Tropical 1423 ( HUA!) ; Municipio de Anorí, corregimiento de Charcón , 500 m, 8 junio 1971 (fl, fr), D. D. Soejarto 1971 ( HUA!) ; Municipio de San Luis, Parque Ecológico Cañón del Río Claro, sector sur, orilla del río, margen izquierda, 325 m, 10 julio 1983 (fr), A. Cogollo & R. Borja 548 ( HUA!). Municipio de San Luis , río Samaná Norte , margen derecha, 360 m, 18 diciembre 2016 (fl, fr), S. E. Hoyos-Gómez et al. 3118 ( HUA!) .