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13 November 2017 Novelties in Adiantum (Pteridaceae) from South America
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Abstract

We describe two new species of Adiantum (Pteridaceae): A. nodosum and A. pseudocajennense. These species occur in the lowland rainforests of the Amazon Basin at 100–350 m in elevation. Both species have laminae 2-pinnate and grow on waterlogged soil in tall swamp forests, but they differ in the rhizome diameter and degree of incision of the pinnule margins. Currently available information suggests that A. pseudocajennense may be endemic to Ecuador, whereas A. nodosum has a wider distribution and is known from Brazil, Colombia and Peru. For both species we present descriptions, distribution statements, comments and illustrations.

Version of record first published online on 13 November 2017 ahead of inclusion in December 2017 issue.

Introduction

Adiantum L. is a large genus described by Linnaeus (1753) with a worldwide distribution (Mickel & Smith 2004). The genus is monophyletic (Rothfels & Schuettpelz 2014; Pryer & al. 2016; PPG I 2016) and has about 225 species. It is characterized by terete, blackish to castaneous petioles, rachises and costae, and sporangia borne on the false indusium (i.e. not on the abaxial laminar surface below it). The rhizomes are short- to long-creeping, usually horizontal, but sometimes compact and suberect, with scales. Laminae are monomorphic or nearly so, pinnate (rarely undivided) to 5-pinnate, sometimes pedate with free or rarely anastomosing veins without included free veinlets and with or without linear epidermal idioblasts (false veins) between the true veins. Sori are formed on the veins of the recurved laminar margins (false indusia), and paraphyses are absent.

Our recent studies and those of others have revealed several new Adiantum species for South America in the last 11 years, e.g.: Peru, one species (Prado 2006); Bolivia, one species (Prado 2006); Argentina, one species (Sundue & al. 2010); Ecuador, one species (McCarthy & Hickey 2011); Brazil, one species (Prado & Hirai 2013); French Guiana, one species (Zimmer 2007); Guyana, one species; and French Guiana, three species (Boudrie & al. 2017).

The two new species described here represent one more step in the process to understand the diversity of Adiantum in the Amazon region.

Material and methods

This study is based on specimens from the following herbaria: AMAZ, COAH, CUZ, INPA, NY, QCA, QCNE, SP, TUR, UC, US and USM. Species recognition was based on morphological characters such as rhizomes, scales, laminar dissection, indumentum and pseudoindusia. We have illustrated the most distinctive characters for each species.

Bracketed geographic coordinates were estimated based on the closest localities, when that information was not given on the specimen label.

The dot-distribution maps are based on all specimens studied for a given species.

Results and Disussion

Adiantum nodosum J. Prado, R. Y. Hirai & A. R. Sm., sp. nov.Fig. 2.

Holotype: Peru, Loreto, Mariscal Ramon Castilla, Río Yaguasyacu, 2–5 km SW from the village of Puerto Izango, primary upland rain forest on a sandy terrace of Río Amazonas, 03°18′S, 72°01′W, 100–150 m, 23 May 1997, H. Tuomisto, K. Ruokolainen, V. Vargas & J. Vormisto 11250 (UC barcode UC1788281; isotypes: AMAZ, SP, TUR 3 sheets, USM).

Morphological descriptionPlants terrestrial. Rhizomes short-creeping, (1.5-)3-5 mm in diam., scaly, with stipes (1-)5-10 mm apart, scales light to dark brown, shiny, lanceolate, margin entire to sparingly denticulate. Fronds (25-)60-76 cm long; stipe black, c. 0.6 × as long as frond, adaxially sulcate, sparsely scaly, scales appressed throughout, dark brown, concolorous, linear, (1-)1.5-2 mm long, base with several processes, margin entire, apex filiform; also with some arachnoid scales c. 0.5 mm long; lamina 2-pinnate, not reduced at base, 15–28 cm wide; rachis with indumentum similar to that of stipe; pinnae elliptic, slightly narrowed at base, tapering at apex, (8-)11-20 × 2-4 cm, indumentum of pinna rachis like that of stipe and main rachis; lateral pinnae in (1 or)2-4(-6) pairs (3–6 pairs in fertile fronds, fewer than 4 in sterile fronds), alternate, ascending; terminal pinna conform, almost as long as or 1-1.2 × as long as subtending pinnae; pinnules in 10–32 pairs, not articulate, conspicuously oblique to pinna rachis, 2-3 × as long as wide, chartaceous, adaxial surface glabrous, abaxial surface sparsely scaly, scales borne on veins, light brown, 0.5-1 mm long, base pectinate, apex filiform and tortuous; pinnules free-veined, without evident midrib, veins slightly prominulous, with oblique idioblasts between veins on both surfaces; proximal pairs of pinnules reduced, somewhat rounded to deltate, medial pairs dimidiate, trapeziform, acroscopic base rectangular, sterile margins irregularly denticulate or serrate, sterile apices obtuse, straight or curved toward pinna apex, fertile apices angular; distal pinnules c. ½ or less length of medial pinnules; terminal pinnule on each pinna broadly rhombic, similar in size or usually longer than distal ones. Sori mostly 5–7(or 8) per pinnule, lunate, oblong; indusia light brown to dark brown, lunate, glabrous, margin entire; spores light brown, trilete.

Fig. 1.

Distribution of Adiantum nodosum and A. pseudocajennense.

f01_237.jpg

Fig. 2.

Adiantum nodosum — A, B: habit; C: sterile pinnule; D: fertile pinnule; E, F: scales from rachis; G, H: scales from abaxial pinnule surface. — A, C, E, G from Tuomisto & al. 12684 (UC); B, D, F, H from Tuomisto & al. 11250 (UC). — Drawn by Klei Sousa.

f02_237.jpg

Distribution and ecology — Amazonian forests in Colombia, Peru and Brazil (Fig. 1). Growing in the flood-plains and banks of creeks on waterlogged and often muddy sites, at 100–350 m. Usually terrestrial, but can also grow on the bases of tree trunks.

Etymology — The specific epithet is based on the morphology of the rhizome, with approximate stipes, leading to a nodose appearance of the rhizomes. This feature is more evident on small specimens where the stipes are 1–1.5 mm apart.

Additional specimens examinedBrazil: Amazonas: Presidente Figueiredo, Distrito de Balbina, margem direita da estrada de acesso à Vila de Balbina, Ramal da Morena, margem do Rio Uatumã, [02°07′06″S, 59°19′07″W], 100 m, 3 Feb 2008, J. Prado & al. 1873 (NY, SP, TUR, US). Pará: Novo Progresso, Fazenda Sr. Sérgio, 15 km Sul de NP pela BR-163, 07.15012°S, 55.41845°W, 8 Dec 2009, F. O. Figueiredo & al. 1372 (INPA). — Colombia: Amazonas: Río Caquetá, 0.5 km E of Estrecho (9 km E of conflu