Merostachys tonicoi Lopes-Neto, P.L.Viana & Vinícius-Silva, 2025

Lopes-Neto, Ray Balieiro, Schindler, Bianca, Figueira, Maurício, Simon, Marcelo Fragomeni, Vinícius-Silva, Ronaldo & Viana, Pedro Lage, 2025, Merostachys tonicoi (Poaceae, Bambusoideae, Bambuseae), a new species at the frontier of Amazonian deforestation in Brazil, Phytotaxa 690 (2), pp. 231-242 : 233-240

Merostachys tonicoi Lopes-Neto, P.L.Viana & Vinícius-Silva , sp. nov. Figs 1–4 .

TYPE:— BRAZIL. Rondônia: Porto Velho, Margem esquerda do Rio Madeira, Inventário T1P 4, 115 m, 09°26’42”S, 64°51’57”W, 03 November 2021 (fl.), B. Schindler et al. 294 (holotype MG barcode MG 249755, isotypes CEN barcode CEN119433, RB, SPF).

Diagnosis: — Merostachys tonicoi is morphologically similar to M. delicatula and M. speciosa , mainly by the shape of the spikelet and lower glume triangular-lanceolate and awned, but differs by the culm nodal line tomentose, with golden trichomes (vs. nodal line glabrous in M. delicatula and M. speciosa ), foliage leaf blade adaxially not ribbed (vs. ribbed in M. delicatula and M. speciosa ), the lower glume 1/4 the length of the spikelet (vs. 1/3–1/ 2 in M. delicatula and 1/ 2 in M. speciosa ), and the spikelet 17–18 mm long (vs. 5.8–10 mm long in M. delicatula and 20–25 mm long in M. speciosa ).

Description: —Caespitose bamboo; rhizomes unknown. Culms initially erect, then arching or leaning on the vegetation; 2–4 m tall, mid-culm internodes 8.6–12.3 × 0.6–0.9 cm, cylindrical, green, hispidulous, with minute yellow trichomes; infra- and supranodal bands of trichomes present, sericeous, trichomes white, infranodal band ca. 0.8 mm long, supranodal band 1–1.5 mm long; walls 1.5–3 mm thick, internal surface yellow; wall thickness:culm diameter ratio = 0.14–0.37; lumen 1.5–5 mm wide; nodes dark brown, not prominent, nodal line tomentose, with golden trichomes 0.8–1 mm long, deciduous, supranodal ridge inconspicuous, glabrous. Culm leaf sheaths 20–29 × 3–4 cm, adaxially glabrous, abaxially sericeous, margins glabrous; auricles absent; fimbriae 4–5 mm long, not fused, sinuous, yellowish; oral setae absent; inner ligule ca. 0.2 mm long, membranous-ciliate; blades not seen. Branch complement consisting of 18–40 branches; branches 21–37 cm long, ca. 1 mm in diameter, not rebranching, internodes 10–12 cm long, glabrous, branch nodes dark brown, not prominent, glabrous. Foliage leaves 4–6 per branch; sheaths 5.3–7 cm long, pubescent, overlapping margins glabrous; auricles absent; fimbriae 6–7 mm long, not fused, straight to sinuous, yellowish; oral setae absent; inner ligule ca. 0.5–0.8 mm long, membranous, truncate; outer ligules ca. 0.2 mm long, membranous, truncate; pseudopetiole 4–5 mm long, dark brown, glabrous; blade 10.3–18 × 1.3–2.6 cm, L: W ratio = 5.3–8.4, lanceolate, adaxially glabrous, not ribbed, abaxially puberulent on the basal portion, glabrescent on the apical portion, with minute yellow trichomes 17–19-nerved, base rounded, asymmetrical, margins scabrous, apex acuminate. Synflorescence borne on leafless (no blades developed) or leafy branches, then with 6–8 well developed leaf blades; racemose, pectinate, 11–13 spikelets; peduncle 15–17 cm long; rachis sericeous; pedicels 1.2–1.5 mm long, sericeous. Spikelets 17–18 × 2.1–2.3 mm, 1-flowered, solitary, ellipsoid; glumes 2, unequal; lower glume 4–6 × 0.8–1 mm, including the awn, awn 1.1–3 mm long, triangular-lanceolate, 1/4 the length of the spikelet, 1-nerved, the nerve prominent and scabrous in the apical half, forming an awn 1/3–1/2 the length of the glume, adaxially glabrous, abaxially sericeous, margins ciliate toward the apex; upper glume 10–11 × 3–4 mm, mucronate, mucro ca. 0.5 mm long, oblong, 2/3 the length of the spikelet, 12-nerved, the central nerve more prominent than the others and scabrous toward the apex, adaxially glabrous, dark-spotted, abaxially sericeous, margins embracing the anthecium, ciliate toward the apex; lemma 15–17 × 3–4 mm, mucronate, mucro ca. 0.5 mm long, oblong, 12-nerved, dull, adaxially glabrous and dark-spotted, abaxially sericeous, margins ciliate toward the apex, apex acute; palea 15–17 × 3–4 mm, oblong, 11- nerved, dull, adaxially glabrous, dark-spotted, abaxially sericeous, margins ciliate toward the apex, 2-keeled, keels scabrous in the middle portion, becoming ciliate toward the apex, apex acute; rachilla extension 9–10 mm long, ciliate toward the apex, rudimentary anthecium present at the apex; lodicules 3, ca. 3 × 1 mm, membranous, margins glabrous, apex acute; stamens 3, filaments ca. 0.5 mm long, glabrous, anthers 9–10 mm long; gynoecium not seen. Caryopsis not seen.

Additional examined material: — BRAZIL. Rondônia: Porto Velho, 10 km a NW de Abunã, margem esquerda do rio Madeira. T11P 5, 125 m, 09°36’39”S, 65°28’04”W, 18 June 2013 (fl.), M.F. Simon et al. 1829 (CEN86840, HUEFS209028 , IAN192375, INPA258921 , RON8238 ) ; Área de supressão da vegetação, AHE Jirau, margem esquerda do rio Madeira , 85 m, 09°17’05”S, 64°42’42”W, 14 October 2012 (fl.), M.F. Simon et al. 1759 (CEN83910, IAN190586, INPA253807, NY2330187 , RON6808 ) ; Margem esquerda do Rio Madeira , 100 m, 09°15’59”S, 64°37’18”W, 20 April 2012 (fl.), G. Pereira-Silva et al. 16146 (CEN81935, HUEFS205534 , INPA251476 , RON5945 ) ; Módulo Abunã , transecto 11, T11 P5., 134 m, 09°36’45”S, 65°28’05”W, 22 July 2011 (st.), G. Pereira-Silva 15918 (CEN81724, HUEFS200621 , IAN191874 , INPA250966) ; Parna Mapinguari , 2014 (st.), A.L.P. Silveira et al. 604 ( MG229918 ,

RON9318); Parque Nacional Mapinguari, Trilha em serra, cerca de 5 km em linha reta da margem esquerda do Rio madeira, seguindo pelo Ramal Vai-quem-quer que leva a Mineração Macisa-São Lourenço (polígono de exclusão), 313 m, 09°32’32”S, 65°02’31”W, 30 July 2014 (fl.), L.L. Giacomin & Y.F. Gouvea 2231 (INPA260903-photo).

Distribution and habitat: —The new species is known from five locations in the municipality of Porto Velho, Rondônia state, southwestern Amazon, Brazil ( Figure 1 ). It is found in the understory of the ombrophilous forest, forming large stands, along the Madeira River ( Figure 2 ).

Preliminary Conservation status: — Merostachys tonicoi has five recorded subpopulations, two of them located within the boundaries of Parque Nacional Mapinguari. The species’ region of occurrence is in an area with a high rate of deforestation, mainly concentrated on the right bank (downstream) of the Madeira River ( Figure 1 ). In addition, one of the subpopulations (Simon et al. 1759) was permanently lost with the formation of the Jirau Hydroelectric dam ( Oliveira et al. 2021) and, because of this, we excluded it from the calculation of AOO and EOO. Another subpopulation (Pereira-Silva et al. 16146) is in intense forest fragmentation and has been lost within its AOO, such that, M. tonicoi has AOO = 16 km 2, EOO = 577 km 2, and only four subpopulations. Therefore, considering its EOO <5,000 km 2, AOO <500 km 2, number of locations ≤ 5, continuous inferred decline in area of occupancy and number of locations, we classify M. tonicoi as endangered EN B1 ab(i) + 2ab(i) under IUCN criteria.

Phenology: —This species was collected with synflorescences in April and October 2012, June 2013, July 2014, and November 2021. Merostachys generally has a reproductive cycle of 30–34 years ( Janzen 1976, Guilherme & Ressel 2001, Liebsh & Reginato 2009, Guerreiro 2014), although the phenology of few species has been analyzed. Our data suggest that the new species has a shorter reproductive cycle (ca. 7 years). However, due to the absence of fertile herbarium specimens prior to 2012, this information is insufficient to determine whether flowering is sporadic. Continuous monitoring of M. tonicoi populations is necessary to confirm this assessment.

Etymology: —Antônio José Barreto dos Santos (1966–2024), born in the state of Acre, was known to everyone as Tonico. He was a woodsman with a deep knowledge of Amazonian flora and participated in countless expeditions, always involved in scientific research and forest inventories. In the region affected by the Jirau dam in the north of the state of Rondônia, Tonico contributed to flora inventories over a decade, climbing big trees and contributing to the collection of more than 3,000 botanical samples. Merostachys tonicoi is therefore a way of honoring his work and highlighting the traditional knowledge of the Amazon people.

Comments: — Merostachys tonicoi can be distinguished from other species of the genus by the sericeous indumentum of the culm leaf sheaths, rachis, pedicels, and spikelets, hispidulous culm internodes, presence of an infranodal band of white trichomes, tomentose nodal line, with deciduous golden trichomes 0.8–1 mm long ( Figure 3 , b), and by the racemose synflorescences with spikelets 17–18 mm long ( Figure 3 , d, f; Figure 4 , e, f), linear-lanceolate, lower glume extending 1/4 the length of the spikelet, with an awn 1.1–3 mm long, 1-nerved, the nerve prominent and scabrous in the upper half ( Figure 3 , g), and dull lemma and palea.

Merostachys tonicoi is the fourth species of the genus recorded in the Brazilian Amazon ( Sendulsky 1997, LopesNeto & Viana 2022). Merostachys fimbriata and M. rondoniensis are only known from their type-localities, in Rondônia state and M. cachimboensis occurs in the states of Mato Grosso, Pará and Rondônia. Merostachys cachimboensis is easily distinguished from the other species by the culm diameter length, absence of the infranodal band of trichomes, and by the linear-lanceolate foliage leaves, ribbed on the adaxial surface ( Table 2). Merostachys fimbriata can be recognized by the glabrous nodes with a conspicuous infranodal ridge, bearing a fringe of trichomes, 4–5 mm long; and M. rondoniensis differs from M. tonicoi by the culm diameter length, indumentum of the culm leaf sheath and foliage leaf sheath, by the shape, number of nerves and indumentum of the lower glume and by the surface of the anthecium ( Table 2).

Due to the proximity of collection on the borders of the states of Acre and Amazonas ( Brazil) and northern Bolivia, it is possible that M. tonicoi could also be found in these regions, particularly in the tributaries of the Madeira River in Bolivia. However, the Andean species of Merostachys can be easily distinguished: M. nigricans by the black internal surface of the basal internodes ( Jiménez-Pérez & Vinícius-Silva 2023), and M. yungasensis by its broadly lanceolate foliage leaves (L:W 4–4.5) and lower glume with a mucronate apex ( Lizarazu et al. 2011). The shape of the lower glume in M. tonicoi is similar to that of M. delicatula Andrade et al. (2020: 72) and M. speciosa Sprengel (1825: 249) . However, it can be differentiated by the lower glume being 1/4 the spikelet length (vs. 1/3–1/2 the spikelet length in M. delicatula and 1/2 the spikelet length in M. speciosa ). Both M. tonicoi and M. speciosa possess sericeous glumes and lemmas but can be distinguished by the indumentum of the rachis and pedicels (sericeous in M. tonicoi and tomentose in M. speciosa ), the spikelet length (17–18 mm long in M. tonicoi vs. 20–25 mm long in M. speciosa ), and the apex of the upper glume (mucronate, ca. 0.5 mm long in M. tonicoi vs. aristate with an awn 2–3 mm long in M. speciosa ). Merostachys delicatula has sericeous rachis and pedicels, smaller spikelets (5.8–10 mm long), a lower glume abaxially glabrous to glabrescent, an upper glume abaxially glabrescent to puberulent and mucronate, a lemma abaxially pubescent, and a palea glabrous on both surfaces ( Table 3).

Otherwise, the new species is easily distinguished vegetatively from M. delicatula by its wider culms, 0.6–0.9 cm wide (vs. 0.1–0.5 cm wide in M. delicatula ), branch complement with 18–40 branches (vs. 72–449 branches per branch complement), and larger foliage leaf blades, 10.3–18 × 1.3–2.6 cm, lanceolate (vs. blades 1.2–6 × 0.2–0.8 cm, linear-lanceolate to lanceolate in M. delicatula ). Merostachys speciosa in turn has culms 1.5–2.5 cm wide, internodes glabrous, sometimes with strigose trichomes (vs. hispidulous in M. tonicoi ) and foliage leaf blades adaxially ribbed, with 1–3 scabrous ribs on one margin (vs. foliage leaf blades adaxially not ribbed in M. tonicoi ) ( Table 3). In addition, both species are recorded only in Eastern Brazil, in the Atlantic Forest domain ( Andrade et al. 2020, Vinícius-Silva et al. 2021b), while the new species is registered so far only in the Amazon domain.

Figures

FIGURE 1. Distribution map of the Merostachys tonicoi (yellow circles). Brazilian states: AM, Amazonas; RO, Rondônia.

FIGURE 2. Habitat of Merostachys tonicoi. a. Banks of Madeira River. b. Forest understory. Photographs by Natália Alves Perigolo.

FIGURE 3. Illustration of Merostachys tonicoi. a. Culm leaf sheath. b. Nodal region detail. c. Culm leaf sheath fimbriae detail. d. Branch complement with foliage leaves bearing synflorescences. e. Fimbriae detail of the foliage leaves. f. Spikelet. g. Lower glume. h. Upper glume. i. Lemma. j. Palea. k. Rachilla extension bearing a rudimentary anthecium.Vouchers:a–c: Pereira-Silva et al. 15918 (IAN191874); d: Simon et al. 1759 (RON00006808); e–k: Schindler et al. 294 (MG249755). Illustration by Ray Lopes.

FIGURE 4. Photographic plate of Merostachys tonicoi. a. Branch complement with leafy synflorescences. b. Nodal region detail of the leafy branches bearing synflorescences. c. Internodes with leafless branches bearing synflorescences. d. Nodal region detail of the leafless branches bearing synflorescences. e. Racemose synflorescence. f. Spikelet. Vouchers: a, c–e: Schindler et al. 294 (CEN119433); b. Simon et al. 1759 (CEN83910). Photographs by Bianca Schindler and Marcelo Fragomeni Simon.