Ernestia rheophytica D.Nunes, J.S.Murillo & Michelang., 2024

Silva, Diego Nunes Da, Murillo-Serna, Jhon S., Hoyos-Gómez, Saúl E., Bernal, Rodrigo, Michelangeli, Fabián A., Braga, João Marcelo Alvarenga & Guimarães, Paulo José Fernandes, 2024, Taxonomic and nomenclatural novelties in Marcetieae (Melastomataceae) from Colombia: A new species of Ernestia and the identity of Acisanthera goudotii, Phytotaxa 677 (2), pp. 109-124 : 110-114

Ernestia rheophytica D.Nunes, J.S.Murillo & Michelang. , sp. nov. ( Fig. 1 )

Type: — COLOMBIA. Caquetá: Solano, Río Yarí, cañón de la Gamitana, -0.246347, -72.426274, 110 m elev., 24 January 2019 (fl., fr.), S. E. Hoyos-Gómez, J. Domine & Abuelo Aurelio comunidad Muinane 3641 ( HUA! barcode HUA 0033312).

Diagnosis: — Ernestia rheophytica differs from all other Ernestia s.s. due to the exclusive combination of the rheophytic condition, pilose indumentum composed of glandular trichomes 0.2–0.3 mm long on the branches, leaves, inflorescence, bracteoles, hypanthium, outer surface of the sepals, and apex of the ovary, and the presence of ovate petals.

Shrub 0.15–0.6 m tall, virgate, rupicolous, rheophytic. Internodes of distal and proximal branches 4–7 cm long, subquadrangular, reddish, covered by a pilose indumentum, glandular trichomes ca. 0.2 mm long. Leaves membranaceous, opposite; petiole canaliculate, 1.5–2.5 cm long, covered by a pilose indumentum, glandular trichomes 0.2–0.3 mm long; mature leaf blades elliptic or lanceolate, 3–5.9 × 1.2–2.5 cm, flat, base obtuse or rounded, apex attenuate; venation acrodromous, basinerved, 3-nerved, central and one or two pairs of secondaries callous plus one pair of inconspicuous submarginal pair that does not reach the apex, tertiary veins mostly percurrent and angled forward, some of them bifurcating; abaxial surface reddish in vivo or beige in sicco, covered by a pilose indumentum, glandular trichomes 0.2–0.3 mm long; adaxial surface dark green in vivo or pale green in sicco, covered by a pilose indumentum, glandular trichomes 0.2–0.3 mm long; margin serrulate with glandular trichomes 0.2–0.3 mm long; immature leaf blades elliptic or ovate, 1.1–2 × 0.4–1 cm, base cuneate, apex attenuate, margin entire. Inflorescences thyrsoid, terminal, erect, indumentum just like on the distal branches, 32–48 flowers per inflorescence; peduncle 2.5–3.2 cm long, rachis 4.3–9 cm long, 2–4 nodes; mature pherophylls on the rachis just like the immature leaf blades; bracteoles elliptic or linear, 1–3 × 0.4–1 mm, concave, patent at anthesis, both surfaces with pilose indumentum, glandular trichomes ca. 0.2 mm long, sessile. Flowers 4-merous, pedicel 5–7 mm long, indumentum as on the rachis, glandular trichomes ca. 0.2 mm long; hypanthium cupuliform, 2.3–2.5 × 2–2.5 mm, outer surface with a pilose indumentum, glandular trichomes ca. 0.2 mm long; sepals narrowly triangular, 1.8–2.6 × 1–1.8 mm, outer surface with a pilose indumentum, glandular trichomes ca. 0.2 mm long, inner surface glabrous; petals ovate, 4.5–5 × ca. 3.5 mm, lilac, apex rounded, glabrous; stamens 8, subdimetric in length (SDI ≅ 0.18–0.20), dimorphic, glabrous; antesepalous stamens with filament 3–3.3 mm long, white, base of ventral appendage ca. 0.5 mm long and bifurcating into 2 aristae, 1–1.3 mm long each that bifurcates only once (a total of 2 ventral aristae), dorsal appendage ca. 0.2 × 0.2 mm, calcarate, positioned in the medial zone of the pedoconnective, pedoconnective 2–3 mm long (ca. 1 mm long from the base to the dorsal appendage + 1–2 mm long from the dorsal appendage to the apex), arched, anther arched, linear-oblong, 2.9–3.6 mm long, yellow, beak ca. 0.3 mm long; antepetalous stamens with filament 2.3–2.7 mm long, white, base of ventral appendage ca. 0.5 mm long and bifurcating into 2 simple aristae, ca. 1.5 mm long each (a total of 2 ventral aristae), dorsal appendage 0.1–0.2 × ca. 0.2 mm, narrowly conical, positioned in the medial zone of the pedoconnective, pedoconnective ca. 0.8 mm long (ca. 0.3 mm long from the base to the dorsal appendage + ca. 0.6 mm long from the dorsal appendage to the apex), arched, anther arched, linear-oblong, 2.2–2.9 mm long, yellow, beak ca. 0.3 mm long; ovary ovoid, 2–3 × 1.3–2.4 mm, 4-locular, superior, apex with pilose indumentum, glandular trichomes ca. 0.2 mm long; axillary placentation, style filiform, 5.3–6.7 mm long, glabrous, white, sigmoid, stigma capitate, ca. 0.3 mm wide. Fruit a loculicidal capsule covered by the hypanthium, globose, 3.7–4.5 × 3.2–3.7 mm, not exceeding the length of the hypanthium, brownish, indumentum and trichomes just like on the ovary; seeds ca. 38, cochleate, 0.3–0.5 × ca. 0.2 mm, brownish, testa with ridges in the raphal-dorsal direction, cells ovoid, foveolate.

Paratype: — COLOMBIA. Caquetá: Solano, Río Yarí, raudal de la Gamitana, -0.224813, -72.459918, 130 m elev., 08 March 2019 (fl., fr.), S.E. Hoyos-Gómez et al. 3705 (HUA! barcode HUA0033311).

Etymology: —The specific epithet rheophytica (from Greek rheo- = pertaining to flowing water, phyt- = relating to plants; see Stearn 1983) refers to the condition of the species, which grows on the rocky banks of the Yarí River and exposed to the water current.

Phenology: —Collected flowering and fruiting in January and March.

Distribution, Habitat, and Preliminary Conservation Status: — Ernestia rheophytica is endemic to Colombia ( Fig. 2 ), known only from two collections, along the banks of the Yarí River in the Department of Caquetá. This species grows in rock crevices on the banks of the river in the rheophytic belt, between 110–130 m elevation. Only two data points on geographic distribution are available, consequently EOO and AOO were not calculated. Therefore, we suggest that the conservation status of E. rheophytica should be categorized as Data Deficient [DD].

Notes: — van Steenis (1981) defined rheophytes as “ plant species which are in nature confined to the beds of swift-running streams and rivers and grow there up to flood-level, but not beyond the reach of regularly occurring flash floods ”. The specimens of Ernestia rheophytica have been found with their roots nestled between rock crevices along the banks of the Yarí River, where the fast currents reach the vegetation. Therefore, it should be categorized as a rheophyte.

Since 2017, two of the authors (SEH-G & RB) have been studying the rheophytic communities in Colombia, documenting its flora ( Hoyos-Gómez & Bernal 2018; Hoyos-Gómez et al. 2023). This research has brought up some interesting new findings in different groups, including a new rheophytic species of melastome, Miconia rheophytica Posada-Herrera & Almeda (2018: 56) , the palm Aiphanes argos R.Bernal, Borchs. & Hoyos-Gómez (in Bernal et al. 2017: 66), and Justicia rheophytica J.R.I.Wood & Hoyos-Gómez (in Wood et al. 2024: 171), all from the same locality, the Samaná Norte River, in the Andes of Antioquia. Also, a new species of Borreria Meyer (1818: 79) ( Rubiaceae ) is being described (pers. comm. Dr. Roberto Salas), from the same locality of Ernestia rheophytica , both growing as rheophytes of the Middle Caquetá River, Colombian Amazonia ( Hoyos-Gómez et al. 2023). These preliminary research on rheophytes in Colombia highlights the importance of ecological and floristic studies that surely will bring more information and new taxa in different groups, including melastomes.

Among the Melastomataceae , rheophytism is rare, now totaling 25 species worlwide (see van Steenis 1981; Costa et al. 2020; Stone 2023; Mendoza-Cifuentes et al. 2024). Most rheophyte melastomes are concentrated in the tribes Miconieae Candolle (1828: 152) and Sonerileae Triana (1866: 457) (six species each), Melastomateae Bartling (1830: 329) (five), and Memecyleae Chamisso (1836: 217) (four), but there are also records in Trioleneae Bacci et al. (2019: 20) and Marcetieae (two each). In Marcetieae , only Macairea linearis Gleason (1931: 417) was known as a rheophyte, a species endemic to the summit of Cerro Duida, Amazonas, Venezuela, growing in the river bed ( Gleason 1931; Renner 1989). Ernestia rheophytica is the second rheophytic species described for the tribe.

Affinities: — Ernestia rheophytica should be considered as a species of Ernestia s.s. (see Rocha et al. 2018) due to its floral merosity, morphology of the androecium and seeds, as well as the presence of an indumentum on the ovary. Among the species of Ernestia s.s., E. karuruana and E. tenella are the species that most morphologically resemble E. rheophytica . The three species sharing subquadrangular branches, leaf blades with attenuated apex, glabrous stamens, and capsules that do not exceed the length of the hypanthium. Furthermore, the length of the hypanthium (2.3–2.5 mm long in E. rheophytica , ca. 2.5 mm long in E. karuruana , and 2–2.5 mm long in E. tenella ), the dimensions of the ovoid ovary (2–3 × 1.3–2.4 mm, ca. 2 × 1.3 mm, and ca. 2 × 2 mm, respectively), and the dimensions of the globose capsule (3.7–4.5 × 3.2–3.7, 4–4.5 × ca. 3 mm, and 3–5 × 3–3.5 mm, respectively) also morphologically approximates these three species.

In addition to the characteristics mentioned above, E. rheophytica shares other characteristics with E. karuruana , such as: the length of the peduncle (2.5–3.2 cm long in E. rheophytica and ca. 3 cm long in E. karuruana ) and the length of the rachis (4.3–9 cm long and ca. 6 cm long, respectively), outer surface of the hypanthium, sepals and apex of the ovary covered by the pilose indumentum, inner surface of the sepals glabrous, antesepalous stamens with a total of 2 aristae on each ventral appendage, and the length of the pedoconnective (2–3 mm long and 2–4 mm long, respectively). However, both species differ due to the indumentum on branches, leaves, bracteoles, peduncle, rachis and pedicels, length of the internodes, petioles, pedicels, antesepalous stamens and style, dimensions and shape of the mature leaf blades, bracteoles, hypanthium and petals, and the number of flowers per inflorescence. These characters are compared in Table 1. Furthermore, both species are not sympatric ( Fig. 2 ).

Ernestia rheophytica is also morphologically similar to E. tenella due to its sessile bracteoles, glabrous petals, antesepalous stamens with dorsal appendage ca. 0.2 × 0.2 mm, concomitantly with overlapping length of the canaliculate petiole (1.5–2.5 cm long in E. rheophytica and 0.8–1.8 cm long in E. tenella ), width of the mature leaf blades (1.2–2.5 cm wide and 1.2–2.6 cm wide, respectively), length of the anther (2.9–3.6 mm long and 3–3.5 mm long, respectively), and length of the style (5.3–6.7 mm long and 4.5–8 mm long, respectively). However, both species are readily differentiated by the indumentum covering branches, leaves, bracteoles, peduncle, rachis, pedicels, outer surface of hypanthium and sepals, length of the internodes, peduncles, rachis, pedicels, sepals and antesepalous stamens, veins on the mature leaf blades, dimensions and shape of the bracteoles and petals, and the number of flowers per inflorescence. These, among other characters, are summarized in Table 1. Furthermore, apparently, both species are not sympatric ( Fig. 2 ).

Figures

FIGURE 1. Ernestia rheophytica. A. Fertile branch. B. Detail of indumentum on the distal branch. C. Abaxial surface of the leaf blade. D. Adaxial surface of the leaf blade. E. Margin of the leaf blade. F. Hypanthium, sepals and pedicel. G. Petal. H. Antesepalous stamen. I. Antepetalous stamen. J. Gynoecium. K. Fruit. L. Seed (lateral view). M. Seed (dorsal view). Voucher: S.E. Hoyos-Gómez et al. 3641 (HUA).

FIGURE 2. Geographic distribution map of Ernestia rheophytica and putative relatives, and E. goudotii. A. Distribution of E. rheophytica (red star), E. karuruana (pink circles), E. tenella (white circles), and E. goudotii (orange circles). B. Habitat of the E. rheophytica on the banks of the Yarí River, Solano, Caquetá, Colombia. Photo: Saúl E. Hoyos-Gómez (B).