Megalastrum mexicanum R.C.Moran & J.Prado
Descripción
A Megalastro atrogriseo squamis petioli angustioribus et lamina utrinque pilis sparsis 1.0–1.5 mm longis vestita differt; etiam praesentia in altitudinibus inferioribus differt.
Rhizomes erect to decumbent; leaves up to 1.3 m long; scales of the petiole bases 15–20 × c. 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 c. 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, c. 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, 35-celled, acicular, spreading, non-glandular; indusia absent.
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Rhizomes erect to decumbent; leaves up to 1.3 m long; scales of the petiole bases 15–20 × c. 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 c. 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, c. 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, 35-celled, acicular, spreading, non-glandular; indusia absent.
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Ejemplar revisado
Chiapas: Cerro del Roblar, near Ixtacomitan, [17°25′ N, 93° 06′ W], 360 m, 12 July 1890, Rovirosa 817 (NY); Hidalgo: below Chapulhuacan, [21°10′ N, 98°54′ W], 0 m, 27 Nov. 1937, Kenoyer s.n. (MO); Oaxaca: Sta. María de Chimalapa, Cabecera del Arroyo Milagrito, c. 13 km SE de Sta. María por la vereda al Río Negro, 16° 51 ′30″ N 94°39 ′0″ W, 400 m, 26 Sept. 1985, Hernández 1616 (NY); Sta. María de Chimalapa, Paso Piedra de Tigre (Cautza), c. 8 km W de Sta. María, 16°53′ N, 94° 43′ W, 220 m, 26 Sept. 1985, Hernández 1962 (MO, NY); Sta. María de Chimalapa, Cabecera del Río Escolapa, c. 15 km S de Sta. María, 16°50′ N, 94°41′ W, 400 m, 21 Oct. 1985, Hernández & González 1704 (NY); Veracruz: San Andrés Tuxtla, Estación Biol. Tropical Los Tuxtlas, 18°34′ N, 95°04′ W, 250 m, 8 Jan. 1987, Sinaca C. 1154 (MO).A
Distribución
México (país) EndémicoA
Elevación
220 – 400 mA
Categoría IUCN
No incluidaB
Categoría NOM-059-SEMARNAT-2010
No incluidaC
Discusión taxonómica
Specimens of Megalastrum mexicanum have previously been identified as M. atrogriseum (e.g., Mickel & Smith 2004). M. mexicanum 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 also differ in geographic distribution and elevation: M. mexicanum is endemic to Mexico (thus the specific epithet) and occurs from 220–400 m, whereas M. atrogriseum is endemic to Costa Rica and Panama and occurs from (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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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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