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Additional Resources:

Family:

Dryopteridaceae (Pteridophyta)

Primary Citation:

Amer. Fern J. 77(4): 127. 1987

Accepted Name:

This name is currently accepted.

Description:

by: R.C. Moran, J. Prado

Type: Costa Rica. San José: Tablazo, [9°50'N, 84°03'W], in 1906, P. Biolley 70 (Holotype: C-n.v.; Isotypes: BM, MO, RB, US)

Description: Rhizomes erect to decumbent; leaves 0.4-1.3 m long; scales of the petiole bases 15-20 × ca. 1 mm, linear, slightly twisted toward the apex, light brown to golden, often shiny, densely denticulate on margins and often on the surfaces; laminae up to 0.8 m long, 3-pinnate-pinnatifid at base, 2-pinnate-pinnatifid medially; basal pinnae 0.2-0.3 m long, strongly inequilateral (elongated basiscopically); pinna rachises abaxially with sparse glandular hairs, moderately scaly, densely pubescent, the glands stalked (representing modified smaller hairs with the terminal cell swollen), the scales to 3-5 × 0.3-0.4 mm long, lanceolate-oblong, flat (not twisted), denticulate, golden brown, shiny, the hairs on the abaxial surfaces of mixed length, 0.2-0.8 (-1.2) mm long, 2-5-celled (6- or 7-celled), the hairs on the adaxial surfaces ca. 0.4-0.7 mm long, 3-5-celled, dense, spreading to erect; costules on both surfaces with indument like that of the pinna rachises; laminar tissue between the veins abaxially pubescent, the hairs 0.2-0.3 mm long, 2- or 3-celled, erect, acicular or (especially in shorter hairs) gland-tipped with a swollen brownish terminal cell) globose sessile glands absent, proscales ca. 0.2 mm long, appressed, sparse, adaxially glabrous, sessile or stalked glands absent; veins evident on both surfaces, pubescent abaxially with hairs like those of the laminar tissue, adaxially very sparsely pubescent, the hairs ca. 1 mm long, 4- or 5-celled, spreading; hydathodes evident; lamina margins ciliate, the hairs 0.2-0.3 mm long, 1- or 2-celled, acicular, mixed with gland-tipped hairs; 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; wet forests, 800-2100(-2800) m.

Comments: The scales on the rachises and costae of Megalastrum atrogriseum are distinctive. They are golden brown, firm, spreading, and mostly flat (i.e., not greatly twisted or tortuous at the apex). Once this scale type is learned, the species is easy to identify. Megalastrum squamosum has similar scales that are far more numerous. In Costa Rica and Panama occurs M. glabrum, which in all respects is like A. atrogriseum except for being glabrous between the veins on the lamina tissue abaxially, and sparser pubescence on the leaf axes abaxially. Megalastrum atrogriseum is highly variable in pubescence of the lamina abaxially. A long-pubescent form has hairs 1.0-1.2 mm long, 6- or 7-celled, and spreading, whereas the form corresponding to the type has hairs 0.2-0.5 mm long, 2-4-celled, mostly erect. We interpret this as variation within the species because no other characteristic correlates with the differences. Furthermore, some forms (such as the type) have mixed stalked-glandular hairs and acicular ones on the abaxial surface, whereas others have mostly acicular hairs. Megalastrum atrogriseum has at least some stalked glands adaxially. These are modified hairs where the apical cell has become clavate or spherical. Often the glandular hairs are shorter than the non-glandular ones. Megalastrum gilbertii (Clute) R. C. Moran, J. Prado & P. H. Labiak, a West Indian species (Moran et al., 2009), also has stalked glandular cells, but these are shorter (ca. 0.1 mm long) and laxer. Megalastrum gilbertii further differs by glabrous pinna rachises abaxially and narrower, more flexuous scales on the rachises and pinna rachises.

Flora and Monograph Treatment(s):

Megalastrum atrogriseum (C.Chr.) A.R.Sm. & R.C.Moran: [Article] Mickel, John T. & Smith, Alan R. 2004. The pteridophytes of Mexico. Mem. New York Bot. Gard. 88: 1-1054.