Megalastrum dentatum A.Rojas

  • Family

    Dryopteridaceae (Pteridophyta)

  • Scientific Name

    Megalastrum dentatum A.Rojas

  • Primary Citation

    Brenesia 68: 17, Fig. 1. 2007

  • Description

    by: R.C. Moran, J. Prado

    Type: Costa Rica. Heredia: NW slope of Volcán Barva, ca. 2 km by road NE of Los Cartagos, 10º09'N, 84º09'W, 2075 m, 16 Mar 1986, M. Grayum & G. Yatskievych 6642 (Holotype: CR-n.v.; Isotype: MO).

    Description: Rhizomes erect to decumbent; leaves 1.5-2.0 m long; scales of the petiole bases 10-20 × ca. 0.5 mm, linear-lanceolate to filiform, twisted, brown, often shiny, prominently denticulate on the margins, the teeth usually antrorse; laminae 0.7-1.3 m long, 4-pinnate-pinnatisect at base (sometimes 4-pinnate), 3-pinnate-pinnatisect medially; basal pinnae up to 0.5 m long, strongly inequilateral (elongated basiscopically); pinna rachises on both surfaces non-glandular (i.e., lacking stipitate glands and sessile spherical ones), scaly, sparsely puberulent, the scales 4-5 × 0.3-0.4 mm, often tortuous, linear-lanceolate, often with flared base, non-bullate, spreading, dark brown, dull or shiny, the hairs on the abaxial surfaces 0.1-0.2 mm long, 1- or 2-celled; costules abaxially puberulent, scaly, non-glandular, the hairs 0.2-0.3 mm long, 1-3-celled, erect, acicular, brownish, the scales 1.0-1.5 mm long, lanceolate (sometimes with an acuminate apex), brown, denticulate, adaxially pubescent, the hairs 0.7-1.0 mm long, 4-6-celled; laminar tissue between the veins abaxially non-glandular, puberulent, the hairs 0.1-0.2 mm long, 1-3-celled, erect, acicular, proscales ca. 0.2 mm long, appressed, adaxially pubescent, especially towards the apex of the segments, the hairs 0.2-0.3 mm long, 2- or 3-celled; veins evident to obscure on both surfaces, hairs and proscales on both surfaces like that of the costules; hydathodes evident; lamina margins ciliate, the hairs 0.1-0.3 mm long, 1-3-celled, non-glandular; indusia minute, fugacious, apparently consisting of a cluster of reddish proscales, ca. 0.1 mm long, protruding from the center of the sorus.

    Distribution: Costa Rica, Panama; 1200-2300 m.

    Comments: Megalastrum dentatum is characterized by densely and conspicuously scaly petioles and rachises, lanceolate scales on the pinna rachises abaxially, and minute (0.1-0.2 mm long) acicular, erect hairs between the veins abaxially. It resembles M. galeottii but differs by leaf axes conspicuously scaly (vs. inconspicuously scaly), and lanceolate scales on the pinna rachises abaxially (versus linear to filiform). When large laminae of both species are compared, M. dentatum appears more finely cut, being 3-pinnate-pinnatisect medially, whereas M. galeottii is 2-pinnate-pinnatisect medially. Megalastrum dentatum also resembles M. squamosum (treated below) by having densely scaly leaf axes. The scales of M. squamosum, however, are quite different, being wider (0.2-0.3 mm), flat (not twisted), straight (not tortuous), and yellow brown. In these respects, the scales of M. squamosum resemble those of M. atrogriseum. Moran 3050 is atypical by lamina tissue between the veins adaxially glabrous or very sparsely pubescent. Typically, the species is pubescent between the veins adaxially, especially toward the segment apices.

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