Myrceugenia linda F.C.S.Vieira & Proença, 2024
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publication ID |
https://doi.org/10.11646/phytotaxa.671.1.4 |
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persistent identifier |
https://treatment.plazi.org/id/038287D9-FF96-FFC1-FF9A-FAD52CB8FAE9 |
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treatment provided by |
Felipe |
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scientific name |
Myrceugenia linda F.C.S.Vieira & Proença |
| status |
sp. nov. |
Myrceugenia linda F.C.S.Vieira & Proença , sp. nov. ( Figs. 2 View FIGURE 2 , 3 View FIGURE 3 ).
TYPE:— BOLIVIA. Santa Cruz: Prov. J.M. Caballero, Siberia, por un camino vecinal saliendo del cruce de Khara Huasi hacia algo abajo y ca. 3-3,5km del camino troncal, 2504m, 17 o 51.22’S, 64 o 40.55’W (DDM), 18 Feb 2003, fl, J.R.I. Wood & M. Mendoza 19079
(holotype: USZ!; isotype: K000565417!).
Diagnosis:—It is distinct from all other species of the genus by the combination of solitary flowers, sub-ancipitate hypanthium, bilocular locules, ovules that are clustered in the central of the locule and 12–13 ovules per locule. Vegetatively it is very similar to Myrcianthes osteomeloides ( Rusby 1895: 36) McVaugh (1958: 768) with which it can easily be confused. The auxotelic raceme with 1–3 pairs of flowers in Myrceugenia linda (vs. a congested, 7–20(–45)- flowered dichasium in Myrcianthes osteomeloides ) and calyx lobes that are subequal in length to the petal globe with thick apices that are slightly cucullate by incipient fusion of the margins in Myrceugenia linda (vs. calyx lobes that are much smaller than the petal globe with rounded apices in Myrcianthes osteomeloides ) allow it to be distinguished from that species when fertile.
Description:— Trees 6–8 m tall, densely branched; trichomes dibrachiate, appressed, sordid white to yellowish. Old branches with rough, fissured bark; young branches densely strigose. Leaves opposite, petiolate; leaf blades 11–20 × 4.75–15 mm, obovate, leaf length/width ratio (1.3–)2–2.4, chartaceous, apex rounded or obtuse, rarely inconspicuously emarginate under magnification, base acute to attenuate, margins finely revolute; upper surface with sparse dibrachiate hairs when young, glabrescent with age, lustrous, with darkish sunken glands; lower surface with yellowish-cream hairs when young, becoming glabrescent with age, with minute, prominent yellowish glands; midvein impressed on the upper surface and prominulous on the lower surface, secondary venation inconspicuous to absent, when perceptible sometimes forming a single marginal vein c. 0.5 mm from the leaf margin, this only perceptible in the middle of the blade; petioles 2–3 mm, usually more or less appressed to the stems, canaliculate. Inflorescence terminal, subterminal at distal nodes or sometimes lateral from old leafless nodes, a congested, reduced, auxotelic raceme with 1–3 pairs of pedicellate flowers. Buds c. 4–4.5 × 2.8–3 mm, pedicels 2.6–3 mm, flattened, strigose; bracteoles persistent to anthesis, 0.9–1.2 × 0.5–0.7 mm, with dark, fringe-like colleters in the axils, length/width ratio c. 3, more or less equalling in length and loosely appressed to the hypanthium, narrowly deltoid-navicular, apex obtuse, externally strigulose with sparse glands, internally glabrous; hypanthium not prolonged beyond the level of insertion of the stamens and style, c. 2 × 1.25 mm, conical, sub-ancipitate, with the thickish ridge perpendicular to the bracteoles, strigulose; sepals c. 2.25 × 2 mm, slightly shorter, equalling or marginally longer than the petal globe, somewhat concave and appressed to the petal globe, in 2 slightly unequal pairs, the outer pair deltoid-ovate, the inner pair ovate, with the central portion thickened and thinner margins, sometimes membranous, ciliate except near the base; both pairs with apex thickened and slightly cucullate by incipient fusion of the margins, externally with scattered translucid glands and sparse trichomes that are denser at the tip, internally glabrous except for a few trichomes that are concentrated under the tip; petals white, c. 2.5 mm in diameter, glabrous on both surfaces, with fine striate lines in dry material; staminal disk 2.75–3 mm wide, squarish, glabrous, very dark brown in dry material and recessed in the centre; stamens semi-curved in bud, c. 156, in c. 4 whorls, filaments 3–4 mm, anthers c. 0.5 mm, oblong, with a minute, translucid apical gland (visible only on very young, closed anthers, hidden in mature anthers), the connective chestnut brown in dry material; locules 2, placenta inserted in the upper half of the locule, with 12–13 closely clustered ovules per locule; style 2.5 mm and geniculate in bud, 5–6 mm when totally extended in the open flowers. Fruit unknown.
Paratype:— BOLIVIA. Santa Cruz. Prov. J.M. Caballero. Siberia, on side road heading S from Comarapa-Siberia highway opposite road to Khara Huasi, 3 January 2000, J.R.I. Wood & D. Goyder 15785 (USZ!, K!).
Phenology:—The specimens were collected with buds and open flowers in January and February; this latter month was cited as a common month for Myrceugenia to flower in Chile (Landrum 1988).
Ecology:—The habitat was described by the collectors as subdominant in cloud forest, at 2504 m elev., or as locally frequent and characteristic of transitional dry ‘ Myrtaceae forest’ lying between wet cloud forest and grassland formations on steep hills at 2300 m above sea level.
Etymology:—The specific epithet commemorates Linda Harris (1945–2022), mother of botanist Stephen A. Harris, to whom the first author is married. Linda also means beautiful in Spanish, reflecting the beauty of all women who become mothers.
Comments:—The suite of characters shown by this species suggests very strongly that it is a species of Myrceugenia : dibrachiate hairs, auxotelic 2–6-flowered inflorescences, flattened pedicels, tetramery, bud shape, persistent clasping bracteoles, anthers semi-curved in bud (sensu Vasconcelos et al. 2015) with a single apical gland ( Landrum & Bonilla 1996), hypanthium not prolonged above stylar insertion, and a 2-locular, multiovulate ovary ( Landrum 1981a). There are however some unusual characters, and the fruit is unknown. The sub-ancipitate hypanthium is unknown in the genus ( Fig. 3 C View FIGURE 3 ). The 2-locular ovary is also much less common than ovaries with 3–4 locules in the genus, as is the placentation. In M. linda the ovules are closely clustered and are attached to a placenta that arises in the middle of the locule. Although this kind of placentation is sometimes present in Myrceugenia , particularly when the locules are unequal ( Landrum 1981a), it is not common; ovules in Myrceugenia are more usually in neat rows along the length of a septum or, if few, are basal ( Gomes-Bezerra et al. 2014, Lucas et al. 2019). Myrceugenia linda is also somewhat reminiscent of Temu cruckshanksii (Hooker & Arnott 1833: 321) O.Berg (1861: 711) : the two species have identical placentation and share semi-curved anthers in the bud and apical glands on the anthers ( Landrum 1986, Vasconcelos et al. 2015). However, M. linda is very different from T. cruckshanksii in most of its other characters, i.e., in its auxotelic inflorescence and persistent, clasping bracteoles. T emu O.Berg (1861: 710), Luma A. Gray (1853: 6) and Nothomyrcia Kausel (1947: 147) are closely related to Myrceugenia and jointly comprise subtribe Luminae E.Lucas & T.Vasconcelos (in Lucas et al. 2019: 565); Myrceugenia and Temu are sister genera (NMWG 2024). Sequencing the DNA of this species (as well as collecting fruiting material) is desirable to confirm its correct generic placement within Myrceugenia but we have few doubts that this is the case.
Biogeography:—The discovery of M. linda obviously raises the question if it belongs to the western or eastern clades or to neither. Geographically, it is c. 1580 km north of the nearest western species, M. correifolia (Hooker & Arnott 1833: 819) O.Berg (1861: 870) (voucher Dillon 5414, see SpeciesLink1), and c. 1165 km northwest of the closest record of an eastern species, M. euosma (O.Berg 1857: 233) D. Legrand (1936: 40) (voucher Schinini 4358, see SpeciesLink2) and c. 1800 km northwest of M. bananalensis Bezerra & Landrum (in Gomes-Bezerra et al. 2014: 38) or M. alpigena var. longifolia (Burret 1941: 532) Landrum (1980: 372) , since they are sympatric in the same forest in Central Brazil ( Fig. 1 View FIGURE 1 ). Myrceugenia bananalensis was not described until 2014 ( Gomes-Bezerra et al. 2014), and so was not included in the phylogenetic studies of Murillo-A. et al. (2012, 2016). However, M. bananalensis was included in a more recent phylogeny ( Amorim et al. 2019) that sampled 33 species of Myrceugenia , and emerged in the eastern clade, as basal in one of its two subclades, i.e., sister to all other species in that subclade. Furthermore, the other taxon of Myrceugenia that has an isolated variety in Central Brazil, M. alpigena var. longifolia , appeared as sister to all other species in the eastern clade ( Amorim et al. 2019). This suggests that such isolated species may be relictual ancient populations that have survived in localized, favourable habitats.
Finding this new species shows that Landrum (1981b: 126) was correct in his speculation that Myrceugenia might occur in the Las Yungas floristic province, and adds Myrceugenia to the list of eight genera of Myrtaceae known to occur there: Amomyrtella Kausel (1956: 514) , Blepharocalyx O.Berg (1855–1856: 512), Eugenia , Myrcia sect. Gomidesia (O.Berg 1855–1856: 6) B.S. Amorim & E. Lucas (in Lucas et al. 2018: 6), Myrcianthes O.Berg , Myrciaria O.Berg (1855–1856: 320), Myrrhinium Schott (in Sprengel 1827: 404), and Siphoneugena O.Berg (1855–1856: 344) ( Landrum 1986, Landrum & Grifo 1988, Proença 1990, Grifo 1992, Quiroga 2010). It also adds a new genus to the flora of Bolivia, and to the flora of the Bosque Tucumano Boliviano. Six of the nine genera (now including Myrceugenia ) of Myrtaceae that occur in the Bosque Tucumano Boliviano also occur in the Atlantic Forest ( Proença et al. 2024) and do not occur in the Chilean Bosque Templado Austral ( Quiroga 2010). This is the dominant pattern, suggesting that the affinities of the Bosque Tucumano Boliviano flora (at least as to its Myrtaceae ) are mainly with the eastern South American flora. Quiroga (2010) reported Blepharocalyx as the only genus occurring in both the Bosque Tucumano Boliviano and the Chilean Bosque Templado Austral. However, the resurrection of Temu due to overwhelming molecular evidence ( Lucas et al. 2007, Vasconcelos et al. 2017, Amorim et al. 2019) has demolished this disjunction. Temu is currently recognized as a monotypic genus endemic to Chile, and a member of subtribe Luminae ( Lucas et al. 2019) , i.e., only distantly related to Blepharocalyx . Three genera that occur in the Bosque Tucumano Boliviano are exceptions to this eastern affinity pattern: Amomyrtella , Myrcianthes and now Myrceugenia . Amomyrtella is unusual in being the only genus to occur in the Bosque Tucumano Boliviano that does not occur in the Atlantic Forest; it has two species, one of which is endemic to the Bosque Tucumano Boliviano and the other a rare element of cloud forests in Ecuador and possibly neighbouring Peru at c. 2400–2600 m elev. (Landrum & Morocho 2011). Myrcianthes occurs in the Bosque Tucumano Boliviano, in the Atlantic Forest and in Chile (as does Myrceugenia ), with the difference that in Chile it has a single highly localized species that occurs only in maritime scrub vegetation near Coquimbo, Myrcianthes coquimbensis (Barnéoud in Gay 1847: 382) Landrum & Grifo (1988: 290), not in the Bosque Templado Austral forests (Landrum 1988, Landrum & Grifo 1988). Myrcianthes coquimbensis is sister to all other species of Myrcianthes ( Retamales 2017, Proença et al., in review) and has in fact been treated as a different genus, Reichea Kausel (1940: 1) . Therefore, the discovery of Myrceugenia linda in the Bosque Tucumano Boliviano has revealed that, as far as we know, Myrceugenia is currently the only genus of Myrtaceae with a disjunct distribution across these three cool, humid forested areas of southern South America, supporting the hypothesis that the genus represents an ancient lineage in the family (Murillo-A. et al. 2016).
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