Myrcia rubiginosa Cambess., Fl. Bras. Merid.

Fernandes, Thiago, Lucas, Eve J., Vasconcelos, Thais Nogales & Braga, João Marcelo Alvarenga, 2025, Extended description and taxonomic notes on two recently rediscovered Myrcia (Myrtaceae) in the Brazilian Atlantic Forest, Rodriguesia (e 00292024) 76, pp. 1-12 : 7-10

2. Myrcia rubiginosa Cambess., Fl. Bras. Merid. (quarto ed.): 300. 1832.

Type: BRAZIL. RIO DE JANEIRO: “ Inter rupes ad rivulum vulgo Carioca prope Rio de Janeiro ” (“ Bois du ruisseau de la Carioca parmi les rocheen ” on the label). [Rio de Janeiro, Tijuca Massif , at the banks of the Carioca River ], 1816–1821, fl., A. Saint-Hilaire A1-670 (lectotype P00161371 , designated by Lucas et al. 2016) .

= Myrcia pyramidata O.Berg, Fl. bras. 14(1): 193. 1857. Type: BRAZIL. RIO DE JANEIRO: “ Habitat in prov. Rio de Janeiro ”, s.d., fl., F. Sellow s.n. (holotype B, probably destroyed; lectotype K000262404!, designated by Lucas et al. (2016); isolectotypes BR0000005238545!, P00161139!, W0037074!).

Figs. 4 ; 5

Trees 4–6 m, usually with multiple trunks, sometimes with pendent branches. Trunk bark greyish light-brown, longitudinally fissured, sometimes detaching in slightly thick, more or less rectangular strips. Apical bud golden to brownish, sericeous, sometimes pruinose, young leaves pinkish, glabrous, young twigs tomentose, sometimes pruinose, the trichomes simple, brownish to ochraceous, ca. 1 mm long.Petioles 6.6– 12 × 1.5–1.8 mm, visible on both surfaces, adaxially sulcate, smooth, often resupinate, when young and mature pilose like the young twigs, occasionally glabrescent; blades 8.5–14 × 3.8–5.6 cm, elliptic, sometimes slightly obovate, rarely narrowly elliptic, chartaceous to subcoriaceous, discolorous, drying greyish-green or olive-green adaxially and light-brown abaxially, apex acuminate, base acute; adaxial surface when young puberulent with appressed, whitish to light-brown, simple trichomes up to 1 mm long, visibly concentrated on the midvein, glabrous when mature or nearly so, midvein finely canaliculate; abaxial surface when young pilose, when mature glabrous or nearly so, the trichomes equal to those on adaxial surface, midvein strongly raised; secondary veins 5–9.5 mm apart, leaving the midvein at angles of 60–65º, marginal veins two, the inner one 1.8–3 mm from the margin, the outer one 0.4–1 mm; glands 0.1–0.2 mm in diameter, homogeneous, hyaline, visible only through a lens on both surfaces, even in young leaves. Conflorescence mostly terminal or axillary, sometimes ramiflorous, comprising a single pair of uniflorescences. Uniflorescence a pendulous, pyramidal panicle, main axis 9.5–15 cm long, secondary branches alternate, the basal one 3.5–10 cm long, peduncle 50–90 × 1–2 mm, all axes slightly flattened, brownish and tomentose (in fresh and dry state), with trichomes like the young twigs, peduncle 51–90 × 1–2 mm, flowers sessile; bracts not examined, deciduous before anthesis; bracteoles 0.5–1 × ca. 0.5 mm, sessile, navicular, ovate, base truncate, apex acute, puberulent to glabrous on both surfaces, deciduous before or occasionally persisting after anthesis. Flower buds 2–2.5 × 1.8–2 mm, obconic, ovary tomentose, the trichomes light-brown, yellowish or amber, in two layers, the lower one papillose, markedly distinct from the calyx, the upper one adpressed, calyx shorter than the petal globe which it is conspicuous at the bud apex. Flower after anthesis with hypanthial cup ca. 0.5 mm deep, internally glabrous except for scattered, yellowish, simple trichomes on the bottom (i.e., top of the ovary), not tearing at anthesis; calyx lobes five, 1–1.2 × 1.5–2 mm, parallel to the disk or reflexed, anthesis by regular opening of the calyx lobes accompanied by some horizontal tearing between the lobes, remaining attached to staminal ring only by the central portion, especially the larger ones, papillose on both surfaces, with trichomes sparse to moderate, yellowish to golden, but internally glabrous at the base at the tearing region, base truncate or trullate (as result of the tearing margins), slightly unequal in size, usually the larger three membranaceous, with rounded apices, the smaller two coriaceous, cucullate in bud, often with acute to apiculate apices, sometimes at least one of these much reduced and slightly displaced below the level of the other lobes; petals five, 1.3–1.5 × 1.2–2.2 mm, rounded or narrowly elliptic, base truncate, apex obtuse or rounded, membranaceous, glands conspicuous, externally puberulent, internally glabrous; floral disk 1.8–2 mm in diameter; staminal ring ca. 0.5 mm in diameter, glabrous; stamens 50–60, filaments 3.3–5 mm long, anthers basifixed, bilocular, with longitudinally dehiscing with thecal margins reflexed exposing the pollen and the entire internal surface of the thecal halves, pseudoseptum visible, the connective eglandular; style 4.5–6 mm long, stigma punctiform, ovary with two locules, each with two ovules. Fruits 6–9.5 × 7–12 mm, globose to subglobose, sometimes with two swellings where the single reniform seed is lodged, green when immature, dark-purple when ripe, surface smooth, glabrous or with scattered trichomes, the pulp white and pleasant to taste; seeds 1–2, reniform, cotyledons green.

Examined material: Maricá , Itaipuaçu , Pico Alto Moirão , 14.I.1982, fl., R.H.P. Andreata 387 (RB). Niterói , Charitas , Parque Natural Municipal de Niterói (PARNIT), Morro da Viração , trilha em direção ao cume da Pedra do Santo Inácio , 22º55’12.6”S, 43º4’39.4”W, 296 m elev., 1.XII.2022, fl., T. Fernandes & R. Benvenuti 1332 (NIT, RB); Itaipu, Parque Estadual da Serra da Tiririca , Córrego dos Colibris, 15.III.2001, fr., E.N.Fontes 1 (RB, RFFP); 14.I.2005, fl., A.A.M. de Barros 2361 (RB); trilha em direção ao cume do morro, 22º57’16.4”S, 43º00’57.6”W, 270 m elev., 10.VII.2022, fr., T. Fernandes 1088 (K, NIT, RB); Piratininga, Tibau, Parque Natural Municipal de Niterói (PARNIT), Morro da Viração, trecho final da travessia Tupinambá, próximo à saÍda da trilha, 22º56’45”S, 43º5’59”W, 60 m elev., 22.XII.2021, fl., T. Fernandes 918 (K, NIT, NY, MBML, RB, RBR); 4.I.2022, fl., T. Fernandes 925 (NIT, NY, R, RB, US); 13.I.2022, fl., T. Fernandes 934 (K, NIT, P, RB, RBR, RFFP); 20.I.2022, fl., T. Fernandes 943 (MBM, NIT, RB, SPF); 28.III.2022, fr., T. Fernandes et al. 1007 (K, NIT, MBM, RB, RBR, RFFP, US) .

Myrcia rubiginosa is endemic to the Brazilian state of Rio de Janeiro, with records restricted to the municipalities of Rio de Janeiro (from the type collection) and Niterói (from the rediscovered populations) ( Fig. 3 ). This species inhabits inselberg forests near the sea at elevations ranging from 60–296 m, in a similar environment of that of Myrcia colpodes , with which it may co-occur ( Fig. 3 ). Flowers can be found from December to January, fruits from March to July.

Myrcia rubiginosa can be recognized in the field by its greyish light-brown trunk and longitudinally fissured bark, detaching as slightly thick, more or less rectangular strips, pinkish and pendular young leaves, pendular uniflorescences (even when flower buds are only beginning to develop) with distinctively brownish and tomentose axes, and relatively small flowers. As previously highlighted by Lucas et al. (2016: 653), the morphology of Myrcia rubiginosa fits the morphological concept of M. sect. Aulomyrcia , specifically the “species group D”, proposed in the same study.

As mentioned earlier, apart from our recent collection effort, Myrcia rubiginosa was collected on three occasions: first in 1982, then in 2001, and finally in 2005. However, in all these instances, the collections were misidentified in herbaria. The 1982 collection (Andreata 387, RB) exemplifies the difficulty in accurately naming a specimen of Myrcia sect. Aulomyrcia . Initially, it was identified as Myrcia macrocarpa De Candolle (1828: 249) , then as M. insularis Gardner (1842: 530) , followed by M. amazonica De Candolle (1828: 250) , and finally as M. rubiginosa . All these species belong to Myrcia sect. Aulomyrcia , although M. insularis and M. macrocarpa are assigned to the “species group A” (see Lucas et al. 2016), and can be distinguished from Myrcia rubiginosa as this species has tomentose inflorescences and flowers (vs. puberulent to glabrous in M. insularis and M. macrocarpa ).

Myrcia rubiginosa is indeed morphologically closely related to M. amazonica , also placed in “species group D” of M. sect. Aulomyrcia (see Lucas et al. 2016). These species share elliptic leaves, well-developed panicles and small flowers. Myrcia amazonica , as currently circumscribed (see Santos et al. 2020), has a wide intraspecific variation and a relatively long list of synonyms. The presence and type of indumentum covering inflorescences and flowers, for instance, are considered polymorphic in t his species. Specimens wit h tomentose inflorescences and ovaries may be more difficult to distinguish from Myrcia rubiginosa , but bark morphology on trunk and branches, along with the inflorescence display, are conclusive features to separate these species. In Myrcia amazonica , the bark on trunk and branches is reddish and exfoliat ing, and in f lorescences are erect in display. In Myrcia rubiginosa , the bark is greyish-brown, longitudinally fissured and detaching as slightly thick, more or less rectangular strips, and inflorescences are pendular.

Figures

Figure 3 – Map with the current known occurrence records ofMyrcia colpodes and M.rubiginosa. White lines represent limits between municipalities in the state Rio de Janeiro.

Figure 4 – a-j. Myrcia rubiginosa in fresh state – a. trunk with rectangular strips; b. leaf adaxial surface (detail: raised midvein); c. leaf abaxial surface (detail: indumentum); d. young leaves; e. flowering branch with pendular inflorescences; f. uniflorescence (point of insertion is omitted, arrowhead points to the peduncle, i.e., first internode); g. lateral axis with flower buds and post-anthetic flowers; h. fruiting branch; i. topside detail of a fruit showing marcescent calyx lobes; j. mature fruit with dry calyx lobes. (a-g. Fernandes 934; h-i. Fernandes 1007; j. Fernandes 1088). Photos: Thiago Fernandes.

Figure 5 – a-e. Myrcia rubiginosa in dry state – a. leaf adaxial surface; b. leaf abaxial surface; c. detail of a typical terminal portion of uniflorescences axes with flower buds; d. open flowers showing the horizontal tearing between the calyx lobes; e. frontal view of an immature fruit. (a-d. Fernandes 934; e. Fernandes 1007).