Myrcianthes O.Berg

Sobral, Marcos, Grippa, Carlos R., Souza, Marcelo C., Aguiar, Osny T., Bertoncello, Ricardo & Guimarães, Thais B., 2012, Fourteen new species and two taxonomic notes on Brazilian Myrtaceae, Phytotaxa 50 (1), pp. 19-50 : 44-46

4. Myrcianthes O.Berg

Myrcianthes O.Berg comprises about 35 species ( Govaerts et al. 2011), mostly from montane habitats from the Andean range, with some species extending to southern South America, Central America, Antilles and United States ( Grifo 1992). It is closely related to Eugenia ( Lucas et al. 2007) , from which it is distinguished mainly by the structure of the embryos, which bear two separate plano-convex cotyledons and a small hypocotyl, instead of fully connate and devoid of hypocotyl, typical of Eugenia .

4.1. Myrcianthes riparia Sobral, Grippa & Guimarães , nov. sp. Type: Brazil, Santa Catarina, mun. Capão Alto, rio Pelotinhas , 50 o 38'38'' S, 28 o 17'19'' W, 19 Nov. 2007, Grupo de estudos de reófitas UHBG 1609 (holotype RB; isotype HBR). Figure 13 .

This species is related to Myrcianthes pedersenii , differing through its glabrous and venose leaves, smaller, glabrous and tetramerous flowers and smaller, purple when ripe, fruit.

Shrub 1.3– 2 m. Twigs cylindrical, glabrous except for the presence of white simple trichomes to 0.2 mm when young; the internodes 3–13 × 0.5 mm. Leaves opposite, petiolate, with two or three pairs of linear colleters 0.3–1 × 0.05 mm at the base of the petioles, the petioles 2–2.8 × 0.6–0.8 mm, glabrous or with simple trichomes to 0.2 mm; blades discoloured, narrowly lanceolate, oblong, obovate to narrowly obovate, 15–34 × 4–11 mm, mostly glabrous except for occasional scattered white trichomes 0.2–0.5 mm on the abaxial side, more densely so in young leaves; translucid glandular dots about 0.1 mm in diam., up to 20 per square milimeter, moderately visible on both sides; apex acute to acuminate, with a visible mucron 0.7–1.5 mm; base cuneate to obtuse; midvein adaxially plane or sligthly prominent and abaxially salient; secondary veins 13 to 20 pairs, departing at 45–60 degrees from the midvein, intersecondary veins visible, with approximately the same diameter as the lateral ones; marginal vein 0.3–0.7 mm from the margin, the margin itself with a thickening to 0.2 mm wide and revolute, sometimes more strongly so proximally. Inflorescences axillary, mostly solitary flowers and occasionally three–flowered dichasia, the pedicels 11–18 × 0.2–0.3 mm, glabrous or with very scattered asymmetrically dibrachiate, appressed trichomes to 0.1 mm, with the basal part somewhat dark coloured; when dichasia present, the main axis 14–15 × 0.4 mm and the lateral ones to 5 × 0.3 mm; bracts and bracteoles glabrous, linear, to 2 × 0.1 mm, deciduous after anthesis but sometimes persisting; flower buds glabrous or with scattered dibrachiate trichomes as the pedicels, pyriform, 3.5–5 × 3–4 mm; calyx lobes four, with white cilia to 0.2 mm and internally with inconspicuous white trichomes to 0.1 mm, lobes markedly unequal, the external ones ovate to triangular, 1–1.2 × 0.9–1.5 mm, the internal ones rounded, 1.5–2 × 3 mm; petals four, white, rounded, 3–3.2 × 3.5 mm, glabrous with marginal cilia 0.2 mm; stamens white, glabrous, up to 70, 3.5–5 mm, the anthers globose, 0.2 × 0.2–0.3 mm, eglandular; staminal ring subquadrate, to 3 mm in diameter, with scattered white trichomes to 0.1 mm; calyx tube absent; style white, glabrous, to 4 mm, the stigma punctiform; ovary bilocular, with up to nine ovules per locule. Fruits globose, 6–7 × 6 mm, purple when ripe, crowned by the persisting calyx lobes; seeds one per fruit, globose to reniform, 6 × 5 mm, about 4 mm thick the testa brown, somewhat shining and easily detachable, the embryo with two clearly distinct plano-convex cotyledons to 5 × 4 mm and ca. 2 mm thick mm and a hypocotyl to 1.5 × 1 mm.

Habitat, distribution and phenology — Myrcianthes riparia is a shrub up to 2 m growing along riparian vegetation of the Pelotas river basin on the highlands of the southern Brazilian states of Rio Grande do Sul and Santa Catarina. Flowers were collected in November and fruits in February.

Conservation status — the municipalities of Capão Alto and Vacaria, with 1330 and 2100 km 2 of area respectively ( IBGE 2012) and about 250 and 430 collections ( CRIA 2012) are scarcely surveyed (each with about 0.2 collection / km 2); additional information from the populations of Myrcianthes riparia is wanting, but it is interesting to note that the specimens cited here are riparian plants and were collected along studies for construction of hydroelectric plants, what may be suggestive of a potential threat for this species; nevertheless, due to the scarcity of information it must be presently scored as DD (Data Deficient; IUCN 2001).

Affinities — this species is apparently related to Myrcianthes pedersenii D.Legrand (for description see Legrand 1962 or Grifo 1992), a species until now known only from field formations of Paraguay, from which it may be distinguished by the following characters:

1. Leaves alternate, opposite or ternate, evidently discoloured, the abaxial surface markedly and evenly covered with trichomes up to 1 mm; lateral veins to 15, interlateral veins more faint and scarcely visible; bracteoles persisting, to 4–8 × 1–2 mm, pilose; flower buds to 10 mm long, densely pilose at least on the ovary; calyx lobes four to five, 3.5–5 × 4 mm; petals four to five, 5–10 mm in diameter; stamens to 300; fruits yellow when ripe, 20–30 mm in diameter. Plants from field vegetation from Paraguay............................................................... Myrcianthes pedersenii

—. Leaves consistently opposite, sligthly discoloured and glabrous or with very scattered trichomes to 0.2 mm abaxially; lateral veins 13–20, interlateral veins evident and with approximately the same width as the lateral ones; bracteoles mostly deciduous after anthesis, to 2 × 0.1 mm, glabrous; flower buds to 5 mm long, glabrous or with scattered trichomes; calyx lobes four, to 1.2 × 1.5 mm and 2 × 3 mm; petals four, to 3.5 mm in diameter; stamens to 70; fruits purple when ripe, to 7 mm in diameter. Plants from riparian habitats in southern Brazilian highlands......................... ........................................................................................................................................................ Myrcianthes riparia

Etymology — the epithet is derived from the Latin word from "margin", alluding to the riverine habitat of the species.

Paratypes: Brazil, Rio Grande do Sul, mun. Vacaria, rio Leão, 20 Nov. 2007, 50 o 57'16'' S, 28 o 10'32'' W, Grupo de estudos reófitas UHBG 978 ( FLOR, HUFSJ), 1,6 m, na margem do rio. Mun. Vacaria , rio Leão , 20 Feb. 2008, C. R . Grippa & T. B . Guimarães 152 ( FLOR, HUFSJ) . Santa Catarina, mun. Capão Alto, rio Pelotinhas , 50 o 38'38'' S, 28 o 17'19'' W, 9 Nov. 2007, Grippa & Guimarães 151 ( FLOR, HUFSJ) .

Figures

FIGURE 13. Myrcianthes riparia — image of holotype (scale — 50 mm). Insert: inflorescences (scale — 10 mm).