Taxon Details: Megalastrum mexicanum A.R.Sm. & R.C.Moran
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Narratives:
Family:
Dryopteridaceae (Pteridophyta)
Dryopteridaceae (Pteridophyta)
Scientific Name:
Megalastrum mexicanum A.R.Sm. & R.C.Moran
Megalastrum mexicanum A.R.Sm. & R.C.Moran
Primary Citation:
Kew Bull. 65: 176, figs. 3 & 4. 2010
Kew Bull. 65: 176, figs. 3 & 4. 2010
Description:
by: R.C. Moran, J. Prado
Type : Mexico. Oaxaca. Mun. Sta. María Cimalapa, ca. 13 km S de Sta. María por la vered al Río Negro que sale a media bajada al cañon de la vereda al Paso Napajo-ua, 16°50'N, 94°40'W, 400 m, 30 Aug 1987, H. Hernández G. 1414 (Holotype: NY-2 sheets; Isotype: CHAPA-n.v.).
Description: Rhizomes erect to decumbent; leaves up to 1.3 m long; scales of the petiole bases 15-20 × ca. 0.3-0.4 mm, linear-filiform, ascending, twisted toward the apex, light brown, often shiny, the margins sparsely denticulate on the margins, the surfaces smooth; laminae up to 0.4-0.88 m long, 3-pinnate-pinnatisect at base, 2-pinnate-pinnatisect medially; basal pinnae 0.15-0.2 m long, strongly inequilateral (elongated basiscopically); pinna rachises abaxially non-glandular, sparsely scaly, sparsely pilose, the scales to 1-2 × 0.1-0.2 mm long, filiform, tortuous, spreading, brown, shiny, sparsely denticulate, the hairs on the abaxial surfaces 2.5-3.0 mm long, 6-10-celled, spreading, the hairs on the adaxial surfaces ca. 2.0-2.5 mm long, 6-8-celled, dense; costules on both surfaces with indument like that of the pinna rachises; laminar tissue between the veins abaxially non-glandular (both gland-tipped hairs and sessile globose ones absent), sparsely pilose, the hairs 0.5-0.8 mm long, 2-5-celled, erect, acicular, proscales sparse, ca. 0.2 mm long, appressed, adaxially glabrous, sessile or stalked glands absent; veins evident on both surfaces, sparsely pilose abaxially with hairs like those of the laminar tissue, sparsely pilose adaxially, typically only 2-4 hairs per vein, the hairs 0.5-0.8 mm long, 2-5-celled; hydathodes evident; lamina margins pilose, the hairs 0.4-0.8 mm long, 3-5-celled, acicular, spreading, non-glandular; indusia absent.
Distribution : Mexico; 220-400 m.
Comments: Specimens of Megalastrum mexicanum has been previously identified as M. atrogriseum (e.g., Mickel & Smith, 2004) It differs from that species by sparser hairs on and between the veins on both surfaces of the laminae and narrower petiole scales (0.2-0.5 mm vs. 0.5-1.5 mm wide). The two species differ in range and elevation: M. mexicanum is endemic to Mexico (thus the specific epithet) and occurs at low elevations (220-400 m), whereas M. atrogriseum is endemic to Costa Rica and Panama and occurs at middle elevations (600-)1000-2000 m. Megalastrum galeotti, which is common in Central America, differs by pinna rachises glabrous abaxially, lamina tissue between the veins abaxially glabrous or (more commonly) puberulent by minute (0.1-0.2 mm long) hairs, and laminar margins with hairs 0.1-0.2 mm long.
by: R.C. Moran, J. Prado
Type : Mexico. Oaxaca. Mun. Sta. María Cimalapa, ca. 13 km S de Sta. María por la vered al Río Negro que sale a media bajada al cañon de la vereda al Paso Napajo-ua, 16°50'N, 94°40'W, 400 m, 30 Aug 1987, H. Hernández G. 1414 (Holotype: NY-2 sheets; Isotype: CHAPA-n.v.).
Description: Rhizomes erect to decumbent; leaves up to 1.3 m long; scales of the petiole bases 15-20 × ca. 0.3-0.4 mm, linear-filiform, ascending, twisted toward the apex, light brown, often shiny, the margins sparsely denticulate on the margins, the surfaces smooth; laminae up to 0.4-0.88 m long, 3-pinnate-pinnatisect at base, 2-pinnate-pinnatisect medially; basal pinnae 0.15-0.2 m long, strongly inequilateral (elongated basiscopically); pinna rachises abaxially non-glandular, sparsely scaly, sparsely pilose, the scales to 1-2 × 0.1-0.2 mm long, filiform, tortuous, spreading, brown, shiny, sparsely denticulate, the hairs on the abaxial surfaces 2.5-3.0 mm long, 6-10-celled, spreading, the hairs on the adaxial surfaces ca. 2.0-2.5 mm long, 6-8-celled, dense; costules on both surfaces with indument like that of the pinna rachises; laminar tissue between the veins abaxially non-glandular (both gland-tipped hairs and sessile globose ones absent), sparsely pilose, the hairs 0.5-0.8 mm long, 2-5-celled, erect, acicular, proscales sparse, ca. 0.2 mm long, appressed, adaxially glabrous, sessile or stalked glands absent; veins evident on both surfaces, sparsely pilose abaxially with hairs like those of the laminar tissue, sparsely pilose adaxially, typically only 2-4 hairs per vein, the hairs 0.5-0.8 mm long, 2-5-celled; hydathodes evident; lamina margins pilose, the hairs 0.4-0.8 mm long, 3-5-celled, acicular, spreading, non-glandular; indusia absent.
Distribution : Mexico; 220-400 m.
Comments: Specimens of Megalastrum mexicanum has been previously identified as M. atrogriseum (e.g., Mickel & Smith, 2004) It differs from that species by sparser hairs on and between the veins on both surfaces of the laminae and narrower petiole scales (0.2-0.5 mm vs. 0.5-1.5 mm wide). The two species differ in range and elevation: M. mexicanum is endemic to Mexico (thus the specific epithet) and occurs at low elevations (220-400 m), whereas M. atrogriseum is endemic to Costa Rica and Panama and occurs at middle elevations (600-)1000-2000 m. Megalastrum galeotti, which is common in Central America, differs by pinna rachises glabrous abaxially, lamina tissue between the veins abaxially glabrous or (more commonly) puberulent by minute (0.1-0.2 mm long) hairs, and laminar margins with hairs 0.1-0.2 mm long.
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