Eugenia longimitra Sobral, M. C. Souza & J. M. A. Braga 2022, sp. nov.
Creators: name: Fernandes, Thiago
name: Giaretta, Augusto
name: Sobral, Marcos
name: Souza, Marcelo Da Costa
name: Braga, João Marcelo Alvarenga
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Myrtales
Myrtaceae
Eugenia
Eugenia longimitra

description: 2. Eugenia longimitra Sobral, M.C.Souza & J.M.A.Braga, sp. nov.
Type:— BRAZIL. Rio de Janeiro: Mangaratiba,Reserva Ecológica de Rio das Pedras (RPPN-IBAMA), Alto da Cabiuna, trilha para a Toca da Aranha, [22°59’20”S, 44°06’15”W], ca. 340 m.s.m., 11 January 1999,J.M.A. Braga, M.G. Bovini & C.M. Mynssen 5125(holotype RB00745117!; isotype HUFSJ!).
Figures 3, 4 and 7.
Diagnosis:—Morphologically similar to Eugenia neoriedeliana M.C.Souza & Giaretta (in Giaretta et al. 2018: 285) that also has calyptrate flowers, but differs by the racemiform inflorescences (vs. fasciculiform in E. neoriedeliana), and flower buds fusiform (vs. obovoid or ellipsoid) and completely fused (vs. partially fused with four vestigial lobes at the apex).
Description:—Tree to 7 m tall, diameter unknown. Stem with slightly exfoliating bark. Young shoots and leaves not seen; cataphylls not seen, probably early deciduous. Young twigs applanate and longitudinally sulcate, glabrescent or puberulent, then the trichomes brownish, asymmetrical, dibrachiate, ca. 0.2 mm, when mature terete or semi-cylindric, brownish to greyish, glabrous; internodes 22–55 × 1–1.5 mm. Mature leaves with petioles 5–7 × 0.8–1 mm, glabrous or very scarcely puberulent, finely sulcate adaxially; blades 9–12 × 2.9–4.6 cm, 2.8–3.4 times longer than wide, elliptic or narrow-elliptic, base cuneate, apex acuminate by ca. 10 mm, chartaceous, the surface irregularly undulate, markedly discolorous, dull light brown adaxially and dull green abaxially, the adaxial side glabrous, the abaxial side very scarcely puberulent, trichomes dibrachiate, ca. 0.2 mm; glandular dots ca. 30/mm², smaller than 0.05 mm in diameter, visible only in the abaxial surface, darker than the surface; midvein finely sulcate adaxially, raised and darker than the surface abaxially; lateral veins 12–16 at each side, leaving the midvein at angles 45–70º, weakly raised and moderately visible on both sides; marginal veins two, the innermost 3–3.5 mm, the outermost about 1 mm from the slightly revolute margin. Inflorescences axillary or terminal, auxotelic, with up to six flowers, the main axis often not extending and so acquiring a racemiform arrangement, in this case the axis 2–3 × 1 mm, or sometimes the main axis extending prolifically and recovering vegetative growth, with trichomes as the twigs, in this case one main axis per axil; bracts ca. 2 × 1 mm, elliptic, concave, deciduous at anthesis; pedicels 10–15 × 1–1.1 mm, applanate, wider at the point of insertion with the flowers; bracteoles 0.8–1.7 × 1–1.6 mm, wide-ovate, glabrous, sometimes connate at the very base, persisting after anthesis. Flower buds 8–10 × 3–3.6 mm, fusiform, uniformly covered by densely appressed brown dibrachiate trichomes ca. 0.2 mm, the calyx completely fused in a very markedly rostrate apiculum, 3–4 mm; often opening through a calyptra at anthesis, or sometimes tearing longitudinally in two irregular halves, simulating two large calyx lobes ca. 3 × 2 mm, glabrous adaxially; petals ca. 3.5 × 3 mm, three in the flower examined, ovate, somewhat unequal between them, glabrous in both surfaces; staminal ring up to 2 mm in diameter, rounded, flattened, glabrous; stamens erect in bud, ca. 100 (scars counted), filaments 3–3.5 mm, the anthers elliptic, 0.3–0.4 × 0.2, with one or two apical glands; calyx tube 0.5–1 mm, with trichomes ca. 0.1 mm around the base of the style; style ca. 8 mm, glabrous, the stigma slightly capitate, minutely papillose; ovary with two internally glabrous locules, each with 4–7 ovules. Fruits not seen.
Paratype:— BRAZIL. Rio de Janeiro: Mangaratiba, Reserva Rio das Pedras (RPPN / IBAMA), trilha para a Toca da Aranha, ca. 260 m. s.m., 24 November 1998, J. M. A. Braga & M. G. Bovini 5085 (RB00745088!).
Etymology:—The specific epithet derives from the Latin ‘ longa ’ (long), and the Greek ‘ mitra ’ (cap, or calyptra), alluding to the length of the calyptra, proportionally longer in this species than in the congeneric ones.
Vernacular name:—The species is regionally known as ‘ameixa-do-mato’ (i.e., ‘wild plum’).
Distribution, habitat and phenology:—Presently known from only two specimens collected in coastal rainforests at 260–340 m elevation in the municipality of Mangaratiba, in the Southwest portion of the southeastern Brazilian state of Rio de Janeiro (Figure 7); flowers were collected in January and November.
Preliminary conservation status:—Data Deficient (DD) considering that only two collections from a single locality are known, and no additional information is available. However, there are some evidences that this species is likely to be threatened at some level. The collection locality and its surroundings are well sampled botanically (see Werneck et al. 2011: 190), but after two decades the species has not been collected again as no further collections were found in herbaria. Despite its occurrence inside a protected area (Cunhambebe State Park), hunting and palm heart extraction are historical threats to its habitat (Medeiros et al. 2004). Thus, we recommend the species to be reassessed if further data are available in the future.
Affinities:— Eugenia longimitra is morphologically related to E. brevistyla, with which it is compared in the diagnosis. It also resembles Eugenia prasina O. Berg (1857 –1859: 225) in its vegetative features, with blades superficially resembling those of this species. However, Eugenia longimitra has the midvein adaxially impressed (vs. raised or rarely plane in E. prasina), and calyx lobes fused in bud, opening through a calyptra or sometimes by irregular longitudinal tearing in two halves (vs. calyx lobes free in bud, opening through four regular lobes).
The dibrachiate trichomes and ovate bracteoles (Figure 4B) of Eugenia longimitra may resemble species of Myrceugenia O. Berg (1855 –1856: 5) with calyptrate flowers, M. gertii Landrum (1984: 163) and M. ovalifolia (O.Berg) Landrum (1984: 163; basionym: Mitranthes ovalifolia O. Berg, 1857 –1859: 356), the former with a rostrate calyptra. However, the calyptrate condition in these species appears along with inflorescences in solitary or superposed peduncles (Landrum 1984), a very recurrent inflorescence pattern in Myrceugenia, whereas Eugenia longimitra has inflorescences with main axis that often does not extend and display a racemiform arrangement with up to six lateral flowers. Alternatively, the main axis recovers the vegetative growth beyond the flowering region (auxotelic growth, Briggs & Johnson 1979: 241) and the flower/fruit become basal in the branch, while the internodes elongate (Figure 4A), a common feature in Eugenia. Furthermore, Eugenia longimitra has 2-locular ovaries in contrast to the 4-locular ovaries found in these species of Myrceugenia, and the number of ovules per locule is lower in Eugenia longimitra (4– 7) compared to that of M. gertii (8–11) and M. ovalifolia (11–16, sometimes 20). Dibrachiate trichomes and calyptrate flowers can also be found in Myrcia De Candolle (1827: 401), but this genus has consistently two ovules at each locule in the ovary (see Lucas et al. 2018). Additional evidence supporting the positioning of Eugenia longimitra are the straight stamens in the flower buds in contrast to the semi-curved stamens of Myrceugenia and the curved stamens of Myrcia (see Vasconcelos et al. 2015).
According to the sectional classification proposed by Mazine et al. (2018), the fused calyx of Eugenia longimitra fits the morphological circumscription of E. sect. Schizocalomyrtus (Kausel 1967: 367) Mattos (2005: 3) —for a taxonomic revision of this section see Giaretta et al. (2021). However, fused calyx has emerged independently several times in Eugenia and it was suggested that calyx features should be combined with other characters to support a reliable phylogenetic placement (Giaretta et al. 2019a, b). Apparently, the fused calyx of E. longimitra fits the homosepalous pattern (bud with calyx fused forming a homogeneous tissue without evidence of seams where the tearing may take place), the most common pattern in Eugenia with fused calyx (Giaretta et al. 2019b). Vegetatively, Eugenia longimitra lacks well-marked veins and has undulate leaf margin, which does not fit the circumscription of E. sect. Schizocalomyrtus. Regarding reproductive characters, the auxotelic inflorescences of E. longimitra are not often found in this section. Therefore, the infrageneric positioning of this species should be confirmed through a molecular phylogeny.
description: Published as part of Fernandes, Thiago, Giaretta, Augusto, Sobral, Marcos, Souza, Marcelo Da Costa & Braga, João Marcelo Alvarenga, 2022, Three new species of Eugenia (Myrtaceae) from the Atlantic Forest of southeastern Brazil, pp. 51-62 in Phytotaxa 552 (1) on pages 54-57, DOI: 10.11646/phytotaxa.552.1.4, http://zenodo.org/record/6673195