Phyllanthus celatus J.C.R. Mendes, J.M.

Mendes, Jone Clebson Ribeiro, Braga, João Marcelo Alvarenga, Fraga, Claudio Nicoletti De, Tomazello-Filho, Mario, Orlandini, Priscila & Athiê-Souza, Sarah Maria, 2024, A new species of Phyllanthus (Phyllanthaceae) hiding in the shades in an urban Atlantic Forest in Rio de Janeiro State, Brazil, Phytotaxa 660 (3), pp. 278-286 : 279-284

Phyllanthus celatus J.C.R. Mendes, J.M. A. Braga & Fraga, sp. nov.

Type:— BRAZIL. Rio de Janeiro: Rio de Janeiro, Parque Nacional da Tijuca, Setor A, na trilha do Morro do Cocanha / Bico do Papagaio , 22º56’56”S, 43º17’19”W, 653 m, 10 August 2021, fl., fr., J.C.R. Mendes, D. Nunes, F.R.M. Fraga & J.M.A. Braga 259 (holotype PEUFR57034!; isotypes MBML!, R!, RB!). Figures 1 , 2 .

Diagnosis:— Phyllanthus celatus differs from congeneric species by having oblong leaves with 10–13 pairs of secondary veins, adaxial surface dark green with minute irregular reddish spots throughout, abaxial surface pale reddish or pale green with marked reddish veins, pistillate pedicels with 9‒12 mm long, and 5-lobed pistillate disk.

Description:— Erect herbs to subshrubs, 20‒80 cm tall, monoecious. Phyllanthoid branching, pinatiform; branches cylindrical, glabrous to minutely with papillae or finely striated longitudinally when dried, light green; internodes 2‒33 mm long. Cataphyllary stipules 1‒3 × 0.5 mm long, linear-lanceolate, apex acuminate, light green or reddish, glabrous. Leaves alternate, simple; petiole 0.5‒1.5 mm long, cylindrical, light green or reddish, glabrous; blade 7‒21 × 4‒10 mm, oblong or rarely oblong-elliptic, base rounded to obtuse, slightly asymmetrical, apex rounded or slightly obtuse apex with an apiculum, membranaceous, margin entire, glabrous on both surfaces; venation brochidodromous, rectilinear, 10–13 pairs of secondary veins mostly straight, ascending at angles ≤ 25°, closed crosslinking with intersecondary veins, areola moderately developed, forming four-five sides, free-ending veins absent; adaxial surface dark green with minute irregular reddish spots throughout, impressed veins, abaxial surface pale reddish or pale green with marked reddish veins. Staminate cymules with 2 to 3 flowers, concentrated mainly in the basal portion of the branches and solitary pistillate flower, concentrated mainly in the terminal portion; bracts 1.5‒2 mm long, linear-lanceolate, apex acuminate, margin entire, light green or reddish. Staminate flowers with pedicel 5‒8 mm long, cylindrical, light green; sepals 5, 2‒3 × 1‒2 mm, uniseriate, widely obovate, apex rounded, concave, pale green with darker green veins, often hyaline; glandular disk 5-segmented, alternisepalous, obtriangular, minutely papillose; stamens 3, filament ca. 1 mm long, completely free, anthers ca. 0.2 mm long, whitish or yellow, connective narrow, thecae lightly emarginate with vertically dehiscence. Pistillate flowers with pedicels 9‒12 mm long, cylindrical, light green; sepals 5, 2.8‒3 × 1.8‒2 mm, accrescent at fructification, uniseriate, elliptic, apex obtuse, concave, pale green with darker green veins; glandular disk deeply 5-lobed, obtriangular, smooth; ovary ca. 1 × 1 mm, globose, 3-loculate, smooth, styles 3, ca. 1 mm long, free, erect, bifid, persistent at fructification, stigmas capitate. Capsules 1.7‒2.5 × 1.7‒2.5 mm, 6-mericarps, subglobose to oblate, pale green to brownish, smooth, pedicel 0.9–1.5 mm long. Seeds 1.2‒2 mm long, trigonous, dark brown, hilum cuneiform, terminal, verrucose lateral and dorsal surfaces, irregular rows arranged longitudinally.

Additional specimens examined (Paratypes):— BRAZIL. Rio de Janeiro: Rio de Janeiro, Bois de la Tijuca, 30 November 1872, fl., fr., A. Glaziou 6124 (P04853826 [image!]) ; Tijuca , 26 July 1888, fl., fr., A. Glaziou & Joãozinho 17757 (NY529041 [image!], P04853822, P04853823 [2 sheets, image!]) ; Parque Nacional da Tijuca, Pico da Tijuca , 22°56’35,5” S, 43°17’11.5”W, 9 February 2022, 975 m, fl., fr., D.A. Zavatin & D.F. Silva 570 ( SPF!) ; ibid., Setor A, margem da estrada Major Archer, Alto da Boa Vista , 22°57’02”S, 43°17’10”W, 600 m, 7 February 2022, fl., fr., D.F. Silva & D.A. Zavatin 390 ( RB!) ; ibid., Floresta da Tijuca, Setor A, na trilha do Morro da Cocanha / Bico do Papagaio , 22°56’59”S, 43°17’41”W, 776 m, 10 August 2021, fl., D. Nunes et al. 499 ( RB!) ; ibid., Caminho Dom Pedro Augusto , 22°57’15”S, 43°17’14”W, 496 m, 7 April 2016, fl., fr., M. Verdi et al. 7408 (CEPEC!, RB!, SP!) .

Etymology:—The specific epithet is a Latin adjective meaning hidden away. It is allusive to the discovery of this species that stayed unknown for centuries in the shadows of the forest, in a place intensely explored by historic and current botanists.

Distribution, habitat and phenology:— Phyllanthus celatus was discovered in an urban remnant of Brazilian Atlantic Forest, in shaded places within the Ombrophilous Dense Forest in an advanced stage of regeneration located at altitudes of 400 to 1,000 m in the Parque Nacional da Tijuca, Rio de Janeiro State, Southeastern Brazil ( Fig. 3 ). Flowers and fruits were collected in February, April, July, August, and November.

Preliminary conservation status:—The new species is presently known only from very few samples collected in Parque Nacional da Tijuca and at one single location (sensu IUCN 2012, 2022). It has an estimated Extent of Occurrence (EOO) of 0.85 km 2 and minimal area of occupancy (AOO) of 4 km ². Regardless of the future discovery of populations of the species in other locations in the Park, the EOO will continue being less than 100 km 2, in view of the extent of available habitat. The Tijuca massif is an area with high endemism and is one of the most well surveyed areas in the Brazilian Atlantic Forest ( Freitas et al. 2006, Pougy et al. 2014). However, the main tourist attractions of the city are concentrated in this place, being visited by thousands of people every year ( Gomes et al. 2021). Although it is an environmentally protected area, the Parque Nacional da Tijuca is located within one of the world’s largest metropolises ( Gerhardinger et al. 2006) and is, therefore, subject to a continuing decline in the extent and/or quality of habitat due to the surrounding urban pressures (see Joly et al. 2014). The increasingly intense and frequent visitations in addition to the constant maintenance of access to tourist spots further promotes the loss of habitat quality due to trampling, soil compaction, introduction of exotic species, and removal of individuals that border the paths inside forest. For these reasons, based on IUCN criteria (2012, 2022), we suggest the Critically Endangered status for P. celatus, CR : B1ab(i, iii)+2ab(ii, iii).

Systematic position and morphological relationships:— Considering the morphological similarities Phyllanthus celatus was allocated to the Phyllanthus subgenus Phyllanthus section Phyllanthus subsection Phyllanthus . Currently this subsection consists of ten species, including recently described species: P. augustinii , P. capixaba Marques-Torres & M. J. Silva (2023a: 310), P. itamarajuensis Marques-Torres & M.J. Silva (2020: 174) , P. lobatus Marques-Torres & M.J. Silva (2023b) , P. longipedicellatus M.J. Silva (2009: 229) , P. longipetiolatus Marques-Torres & M.J. Silva (2022b: 288) , P. megastylus Marques-Torres & M.J. Silva (2023c: 186) , P. niruri , P. perpusillus Baillon (1865: 358) , and P. platystigma Marques-Torres & M.J. Silva (2023b) . This subsection is characterized by its linear-lanceolate cataphyllary stipules, leaf blades asymmetrical at the base, staminate and pistillate flowers with five sepals, staminate flowers with three free or proximally connate stamens, vertically, obliquely, or horizontally dehiscent anthers, and a cupuliform pistillate disk ( Webster 2002, Bouman et al. 2022).

Morphologically, Phyllanthus celatus has a close affinity with P. niruri , a species widely distributed in America, but differs in the following characteristics: a dark green adaxial surface of the leaf blades with minute irregular reddish spots throughout and pale reddish or pale green abaxial surface with marked reddish veins (vs green on both surfaces in P. niruri ), 10‒13 pairs of secondary veins (vs 6‒9 pairs), closed crosslinking (vs open), intersecondary veins (vs absent); staminate flower pedicels 5‒8 mm long (vs 2–4 mm long); staminate sepals 2‒3 × 1‒2 mm (vs 1‒2 × 0.5‒1 mm); minutely papillose staminate glandular disc (vs verrucose or papillose); pistillate flower pedicel 9‒12 mm long (vs 3–5 mm long); pistillate sepals 2.8‒3 × 1.8‒2 mm (vs 1.2–2 × 0.5 mm); and a deeply 5-lobed pistillate glandular disc (vs entire, patelliform).

Phyllanthus celatus resembles the poorly known and sympatrically occurring P. augustinii , whose type of material is from the state of Rio de Janeiro. Webster (2002) mentions that the collection Glaziou 17757 (K, P) has unusually larger flowers and may represent P. augustinii . Therefore, these specimens represent P. celatus , which differs from P. augustinii mainly by having an erect and herbaceous to subshrubby habit, plants 20‒80 cm tall (vs subshrubby habit, 15–18 cm tall in P. augustinii ), oblong or rarely oblong-elliptic leaf blades 7‒21 × 4‒10 mm (vs elliptic, obovate or elliptic-obovate 20–40 × 10–20 mm); staminate flower pedicel 5‒8 mm long (vs 9–10 mm long); stamen filament ca. 1 mm long (vs 2‒3 mm long); pistillate flower pedicel 9‒12 mm long (vs 20–30 mm), and deeply 5-lobed glandular disc (vs entire, cupuliform). Even so, Phyllanthus celatus is similar to the recently described species P. lobatus as it is the only one that has a lobed pistillate disc, but it differs mainly due to the presence of primary, secondary and intersecondary veins evident on the leaf (vs absent in P. lobatus ), pistillate sepals light green (vs whitish or slightly pinkish), deeply 5-lobed pistillate glandular disc (vs 3–5-lobed), styles erect (vs curved), and geographic distribution restricted to the Southeast (vs South). The differential characteristics of the four congeneric species are summarized in Table 1 , and comparative photos in fields of P. augustinii and P. niruri are presented in Figure 4 ; and for P. lobatus see Torres & Silva (2023b).

Figures

FIGURE 1. Phyllanthus celatus. A. Habitat, B. Habit, C. Branches showing both leaf surfaces (adaxial and abaxial), D. Pistillate flowers with details, E. Developed fruits. (Photographs by JCR Mendes).

FIGURE 2. Phyllanthus celatus. A. Habit, B. Leaf, C. Staminate flower, D. Pistillate flower, E. Gynoecium [detail of the pistillate disc], F. Fruit, G. Seed. (Drawing based on the holotype, made by Regina Carvalho).

FIGURE 3. Geographic distribution of Phyllanthus celatus.

FIGURE 4. A–C. Phyllanthus niruri. A. Branches with pistillate flowers and fruits, B. Staminate flowers, C. Pistillate flowers. D–H. P. augustinii. D. Habit, E–F. Staminate flower. G. Pistillate flower. H. Fruits. (Fotos: A. Otávio Marques, B–C. Joyce Assunção; D–H. Jone Mendes).