Arthrostylidium cachimboense Lopes-Neto & P.L.Viana, 2022

Lopes-Neto, Raimundo Balieiro & Viana, Pedro Lage, 2022, Flora of the Serra do Cachimbo (Eastern Amazon, Brazil): Bambusoideae (Poaceae), including the description of two new species, Phytotaxa 550 (2), pp. 99-129 : 104-106

Arthrostylidium cachimboense Lopes-Neto & P.L.Viana , sp. nov. Figs 3–4 .

Type :— BRAZIL. Pará : Altamira , Reserva Biológica Nascentes da Serra do Cachimbo, Ramal principal da REBIONSC, mata ciliar, 589 m, 9°04’26.6”S, 54°45’18.3”W, 25 May 2021, Lopes-Neto et al. 682 (holotype MG!, isotypes INPA!, RB!) .

Diagnosis: — Arthrostylidium cachimboense is morphologically similar to Arthrostylidium auriculatum Londoño & Clark (1998: 410) in having true auricles on the foliage leaves, but differs in its fistulose culms, with several membranous delicate septa in the lumen (vs. without septa in the lumen), foliage leaf auricles 1–2 mm long, blackish (vs. 1.5–2.5 cm long, purplish brown), fimbriae 9–11 mm long, copperish (vs. 5–8 mm long, purplish to brown), and blades 25–26 × 4.2–4.8 cm, broad-lanceolate and abaxially short-pilose (vs. 5–16 × 1.2–2.5 cm, lanceolate to linearlanceolate and abaxially tomentose).

Rhizomes pachymorph, necks 2–4.5 cm long. Culms 5–6 m long, 4–6 mm in diameter, erect at the base, leaning on the vegetation in the upper portion, internodes 42–49 cm long, fistulose with several membranous delicate septa in the lumen, smooth, glabrous; buds subequal, triangular, prophyll unitary, 3–7 × 2.1–2.8 mm, sparsely pilose, margins ciliate; nodes black, glabrous, nodal line horizontal, with a corky flange ca. 1 mm long and blackish usually present at the culm leaf insertion, supranodal ridge slightly conspicuous. Branch complement with principal branch 42–60 cm long, ca. 3 mm in diameter, secondary branches smaller, 22–28 cm long, ca. 2 mm in diameter. Culm leaves persistent or tardily caducous; sheaths 8.9–10 × 1.3–1.5 cm, confluent and shorter than the blade, light green with dark green spots, stramineous in siccus on both surfaces or sometimes pinkish on the abaxial surface, glabrous, lateral margins shortly pilose on both sides, trichomes black, margins scabridulous, summit slightly asymmetrical on opposite side of the auricle; auricle present on one side, alternating along the culm, 1.8–2.2 mm long, tongue-shaped; fimbriae ca. 2–2.5 mm long, sinuous, stramineous; inner ligules ca. 1 mm long, symmetrical, membranous-ciliate; blades 21–24.2 × 1.5–2 cm, lanceolate, stramineous on both surfaces or sometimes pinkish on the abaxial surface, occasionally with black spots toward the apex on the adaxial surface, sparsely scabridulous with yellowish trichomes, margins glabrous, apex acuminate. Foliage leaves (4-)7–9 per complement; sheaths 4–4.5 × 1 cm, light green with dark green spots, glabrous, margins glabrous except in one upper margin ciliate; auricles present, equal on both sides, 1–2 mm long; fimbriae 9–11 mm long, straight at the base and sinuous toward the apex, copperish, shiny; inner ligules ca. 0.2 mm, symmetrical, membranous-ciliate; outer ligules ca. 0.2 mm, symmetrical, membranous; pseudopetioles ca. 4 mm, flat, glabrous; blades 25–26 × 4.2–4.8 cm, LW: 5–5.4, broad-lanceolate, green, glabrous on the adaxial surface and shortly pilose with whitish trichomes in the abaxial surface, 47–49-nerved, midnerve central, base obtuse, asymmetrical, margins glabrous to scabridulous toward the apex, apex acuminate. Synflorescence not seen.

Distribution and habitat: —This species was only collected in one locality, in a riparian open ombrophilous forest (mata ciliar) fragment at the headwaters of the Curuá River in REBIONSC, Altamira, Pará.

Conservation status: —According to the IUCN Red List Categories and Criteria (2019), the new species should be considered as Data Deficient (DD) status, because it is only known from its type specimen. However, it was collected in a forest fragment near the main road of REBIONSC, a region threatened by agricultural activities. New expeditions are needed to increase the knowledge on its distribution and the conservation status assessment.

Etymology: —The epithet refers the type-locality, in the Serra do Cachimbo.

Comments: — Arthrostylidium cachimboense is recognized by its fistulose culms, with several membranous delicate septa in the lumen, the culm leaf sheath summit slightly asymmetrical on the side opposite of the auricle, an auricle present on one side, alternating along the culm, 1.8–2.2 mm long, tongue-shaped and fimbriae ca. 2–2.5 mm long, sinuous, stramineous, blades 25–26 × 4.2–4.8 cm, lanceolate with apex acuminate and foliage leaves bearing auricles 1–2 mm long, blackish, fimbriae 9–11 mm long, copperish and blades 25–26 × 4.4–4.8 cm, broad-lanceolate, abaxially short-pilose. The new species and Arthrostylidium auriculatum are the only ones in the genus with auricles on the foliage leaves. The latter is only known from the type-locality in municipality of Amalfi, at the northern extreme of Central Cordillera of Colombia and can be distinguished from A. cachimboense mainly by characters of the culm interior and foliage leaves, including the color of the auricles and fimbriae, blades size and abaxial indumentum ( Table 1 ).

The new Serra do Cachimbo species also differs from its Amazonian Brazilian congeners by the nodal line bearing a horizontal corky flange ca. 1 mm long (vs. a downward shield-like corky flange in Arthrostylidium scandens McClure in Maguire & Wurdack 1964: 4); nodal fimbriae absent (vs. a uniform band of abundant whitish-yellow cilia up to 5 mm long in A. fimbrinodum Judziewicz & Clark 1993: 84 ); culm leaf blades 21–24.2 cm long, lanceolate and apex acuminate (vs. 2.5–2.8 cm long, triangular lanceolate and apex setose in A. simpliciusculum ) and foliage leaf sheath extension absent, inner ligule ca. 1 mm long, auricle symmetrical and fimbriate (vs. sheath extension up to 5 mm long on one side, inner ligule elongate on opposite side of the sheath extension, 6–10 mm long and auricle and fimbriae absent in A. grandifolium Judziewicz & Clark 1993: 88 ). The latter has, along with A. cachimboense and A. chiribiquetensis Londoño & Clark (1998: 412) (known from the Serranía de Chiribiquete, department of Caquetá, Southeastern Colombia), the largest foliage leaf blades known for the genus so far, but A. chiribiquetensis can be distinguished by the pithy, canaliculate culms, the basally inflated culm leaf blades and foliage leaf blades tessellate, bearing reddish fimbriae.

Figures

FIGURE 3. Illustration of Arthrostylidium cachimboense: A. Rhizomes. B. Culm interior with several septa in the lumen. C. Bud frontal view. D. Bud lateral view. E. Corky flange at the insertion of the culm leaf. F. Branch complement frontal view. G. Branch complement lateral view. H. Culm leaf, adaxial side. I. Detail of the fimbriate auricle in the culm leaf. J. Foliage leaf complement. K. Detail of the fimbriate auricles in the foliage leaf. Drawn by R.B.Lopes-Neto, based on the holotype [Lopes-Neto et al. 682 (MG)].

FIGURE 4. Field photographs of Arthrostylidium cachimboense:A. Habit. B. Culm interior with several septa. C–E. Branch complement. F–G. Culm leaves. H. Foliage leaf complement. I–J. Detail of the fimbriate auricles of the foliage leaves. Photos: A.S.B.Gil (A) and P.L.Viana (B–J).