Adiantum obliquum Willd.

  • Authority

    Mickel, John T. & Smith, Alan R. 2004. The pteridophytes of Mexico. Mem. New York Bot. Gard. 88: 1-1054.

  • Family

    Pteridaceae

  • Scientific Name

    Adiantum obliquum Willd.

  • Description

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    Species Description - Rhizomes short-creeping, 3–4 mm diam.; rhizome scales lustrous, castaneous, entire to denticulate, 2.5–3 x 0.5 mm, margins with short teeth; fronds clumped, 25–70 cm long, arching; stipes black, lustrous, to ca. 35 cm x 1–2.5 mm, ca. 1/2–2/3 the frond length, with numerous hairs and hair-like scales to 2 mm long; blades oblong to oblong-deltate, 1-pinnate (ours), occasionally the blades with a pair of 1-pinnate proximal pinnae smaller than the terminal part of the blades; rachises atropurpureous, with dense, tan, filiform, contorted scales and hairs; pinnae 6–12 pairs, ovate-lanceolate, proximal pinnae often largest, short-stalked to 5 mm, inequilateral, largest pinnae 3.5–7 x 1.5–2.5 cm, bases oblique, excised basiscopically, rounded acroscopically, apices acuminate, margins finely denticulate to unevenly biserrate, midveins close to middle of pinnae, nonarticulate; veins free, forking, ending in teeth; indument adaxially absent, abaxially of pectinate, hair-like scales to ca. 1 mm, not glaucous; idioblasts present on both blade surfaces; sori to ca. 20 along both acroscopic and distal portions of basiscopic margins; indusia 2–6 mm long, glabrous or often with numerous short hairs to ca. 0.3 mm long.

  • Discussion

    Lectotype (chosen by Lellinger, Mem. New York Bot. Gard. 23: 13. 1972). Venezuela. Caracas, Bredemeyer s.n. (B-Willd. 20067, sheet 1!).

    The 1-pinnate species (A. obliquum-petiolatum complex) are in need of careful revision over their entire range. Material identified as this species from Oaxaca by Mickel and Beitel (1988) is mostly A. petiolatum. Adiantum obliquum and A. amblyopteridium may have formed the fertile hybrid A. oaxacanum (which see), which is intermediate in morphology. The rounder apices, reduced basal pinnules, and tan spores (easily seen against a white background) distinguish A. oaxacanum from A. obliquum. Occasional specimens of A. obliquum are bipinnate with a single pair of 1-pinnate lateral pinnae: Herna´ndez G. 1751, 1828 (NY), from Oaxaca. In such cases, the terminal pinna is larger (longer and wider) than the lateral pinnae.

  • Distribution

    Terrestrial in wet, tropical rain forests, lowland forests, calcareous soils; 100–600 m. Mexico; Guat, Bel, Nic, CR, Pan; Gr & L Ant; Col, Ven, Trin, Tob, Guy, Sur, Fr Gui, Ec, Peru, Braz, Bol.

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