Triplophyllum juruenense M.G. Nunes & Labiak, 2025

Nunes, Mauricio G., Prado, Jefferson, Hirai, Regina Y. & Labiak, Paulo H., 2025, Triplophyllum juruenense (Tectariaceae), a new species of fern from Southern Amazonia, Phytotaxa 706 (3), pp. 289-295 : 290-293

Triplophyllum juruenense M.G. Nunes & Labiak , sp. nov. ( Figures 1 A–I , 2 C–F )

Type:— BRAZIL. Mato Grosso: Cotriguaçu, Parque Nacional do Juruena , trilha da Cobra, 09º01’21” S, 58º37’05” W, 170 m, 19 May 2018, P. H. Labiak 7163, with R. C. Forzza, R. Goldenberg, D. L. Santos-Silva, L. P. Piva & E. W. S. Gonçalves (holotype UPCB; isotypes HERBAM, RB, RON) .

Diagnosis: Triplophyllum juruenense is distinguished by its 2- or 3-pinnate-pinnatifid, chartaceous, and light green fronds. Both surfaces of its laminae and veins are puberulent to pubescent, featuring two distinct hair sizes on the abaxial side of the main axes: smaller hairs (0.2–0.4 mm long, 2–4[5]-celled) and longer hairs (0.4–0.5 mm long, 6–8- celled). Its indusia are puberulent, with very short hairs (up to 0.1 mm long) concentrated in the center and along the margin. Triplophyllum crassifolium ( Holttum 1986: 257) is a similar species, but differs by having coriaceous, dullgreen fronds. Its laminar tissue and veins are pubescent on both surfaces, with uniformly sized hairs (0.5–1 mm long, 5–9-celled) on the abaxial side of the main axes. Furthermore, its indusia are pubescent, characterized by central hairs 0.3–0.4 mm long and marginal hairs 0.5–0.6 mm long.

Description. Plants terrestrial. Rhizomes creeping, 0.4–0.8 cm in diameter, scaly, the scales lanceolate, entire to ciliate at the margin, light brown to brown, 1.3–1.8 × 0.7–0.8 mm. Fronds monomorphic, puberulent to pubescent; petioles 12–27 cm × 1.8–2 mm, stramineous to dark brown, with few lanceolate scales, the scales light brown to brown, 1.5–3 × 0.4–0.5 mm, pubescent, the hairs catenate, whitish to light-brown, 0.2–0.3 (0.4) mm long, 3–4(5)-celled; laminae deltate, 17–22 × 24–30 cm, with 10–15 lateral pinnae, 2 or 3-pinnate-pinnatifid at the base and 2-pinnate-pinnatifid above, gradually reduced towards the apex, chartaceous, light green; rachises pubescent on both surfaces, more densely so on the abaxial side, hairs whitish to light brown; hairs on the abaxial side of two sizes, the shorter ones 0.2–0.4 mm long, 2–4(5)-celled, the longer ones, 0.4–0.5 mm long, 6–8-celled; hairs on the adaxial side of the rachises sparse, longer, 0.8–1.2 (1.5) mm long, 8–10(12)-celled; basal pinnae 11–18 cm long, more than 0.6 times the length of the lamina, strongly elongate basiscopically; pinnae rachises castaneous, pubescent in both surfaces, the hairs similar to those on the rachises in distribution and sizes, basal pinnules elongate, ca. 3 or 4 times longer than the acroscopic pinnules; last segments rounded to obtuse, margins sparsely ciliate, the cilia 2–5 mm long, 3–4(5)-celled; veins dark brown, visible on both sides, puberulent to pubescent on both surfaces, the hairs catenate, light brown, similar in size of those on the rachises on the abaxial and adaxial side; laminar tissue puberulent on both surfaces, the hairs whitish to light brown, 0.2–0.3 mm long, 2 or 3-celled. Sori rounded, supramedial; indusia orbicular-reniform, light brown, opaque, ca. 0.3–0.5 mm wide, puberulent, the hairs 0.1 mm long, and minutely ciliate, the cilia 0.1 mm long.

Distribution and ecology:— Triplophyllum juruenense occurs in Northern Mato Grosso state, in the southern limits of the Brazilian Amazon Forest ( Figure 3 ). It occurs as terrestrial in the understory of shaded and humid forests.

Etymology: —The name refers to the Juruena River basin, one of the largest in Mato Grosso state. The Juruena River flows from the Central portions of Brazil into the Amazon, where it joins the Teles-Pires River to form the Tapajós , one of the main tributaries of the Amazon River. Due to the rocky and steep terrain, the Juruena River features numerous waterfalls and rapids ( Figures 2 A and 2 B ), unlike most rivers in the Amazonian lowlands.

Paratypes:— BRAZIL. Mato Grosso: Apiacás, Parque Nacional do Juruena, Fazenda Soberana , 09º07’26”S, 57º51’25”W, 380 m, 07 October 2021, P. H. Labiak et al. 7769 ( HERBAM, NY, RB, UPCB) ; Nova Bandeirantes, Parque Nacional do Juruena, trilha do Saruê , parcela permanente do Programa de Monitoramento da Biodiversidade do ICMBio, 08º57’38”S, 58º43’42”W, 170 m, 17 May 2018, P. H. Labiak et al. 7121 ( HERBAM, RB, UPCB) .

Taxonomic Discussion:— Triplophyllum juruenense is mainly characterized by having a puberulent to pubescent frond, with hairs distributed on the petiole, rachis, pinnae rachises, veins, and laminar tissue ( Figure 1A–I ). The hairs on the abaxial side of the rachis are variable in length: the shorter ones are 0.2–0.4 mm long, 2–4(5)-celled, whereas the longer ones are 0.4–0.5 mm long, and 6–8-celled ( Figure 1 F–G ). On the adaxial side of the rachis, the hairs are sparse and longer, 0.8–1.2 (1.5) mm long and with 8–10(12)-celled. The laminar tissue is also puberulent on both surfaces, with hairs that are whitish to light brown, 0.2–0.3 mm long, and 2- or 3-celled. It is a medium-sized species of Triplophyllum , with 2- or 3-pinnate-pinnatifid, chartaceous, and light green laminae ( Figure 2 C–F ).

The most similar species is Triplophyllum crassifolium , which shares with T. juruenense the presence of hairs on the laminar tissue and veins, ciliate lamina margins, and long, pluricellular, catenate hairs on the rachis, especially on the adaxial side. It differs from T. juruenense in having coriaceous laminae (vs. chartaceous), the hairs of pinnae rachis on the abaxial side are uniform in size,> 0.5 mm long (vs. two sizes, up to 0.5 mm long), laminar tissue on both surfaces with hairs> 0.5 mm long (vs. <0.5 mm long), and indusia with long and ciliate margins (the cilia equal to or longer than the indusium width vs. cilia smaller than the indusium width).

The chartaceous,light green laminae, the presence of hairs, and the obtuse segments resemble those of Triplophyllum dicksonioides ( Fée 1869: 143) Holttum (1986: 257) , which is distinct by having spherical, yellowish glands on the axes, laminar tissue, and indusia (glands are absent in T. juruenense ). Additionally, the hairs on the pinnae rachises abaxially in T. dicksonioides are smaller, ranging from 0.1–0.2 (0.5) mm long, 1–3(5)-celled. Triplophyllum boliviense Prado & Moran (2008: 106) is also similar but differs in the presence of glands on the veins, the abaxial side of the laminae, and the indusia.

Figures

FIGURE 1. Illustration of Triplophyllum juruenense based on the holotype. A. Habit. B. Detail of the petiole with hairs and scales. C. Rhizome scale. D. Abaxial side of a pinnule. E. Adaxial side of the rachis. F. Hair from the laminar tissue. G. Hair from the rachis. H. Detail of the abaxial side of a pinnule. I. Sori showing the indusium, sporangia, hairs, and cilia on the indusium. (A–I: Labiak et al. 7163, UPCB). Illustrations by Diana Carneiro.

FIGURE 2. The Juruena National Park and details of Triplophyllum juruenense. A. Salto Augusto waterfall. B. Rocky boulders and a waterfall in a small affluent of the Tapajós River. C. Habit and adaxial side of the frond. D. Habit and abaxial side of the frond. E.Abaxial side of a pinna. F. Detail of a pinnule showing veins, sori, and hairs on the veins and laminar tissue. (photosA and B by P.H. Labiak; photos C–F by R. Goldenberg).

FIGURE 3. Distribution map of Triplophyllum juruenense.