Megalastrum adenopteris (C.Chr.) A.R.Sm. & R.C.Moran

Description

by: R.C. Moran, J. Prado, and P.H. Labiak

Lectotype: (designated by Moran et al, 2009): Brazil. Rio Grande do Sul: Silveira Martins, Val Veneta, ad terram silvae primaevae, in 1893, Lindman s.n. (Regnell A 1313) (BM-00907710; duplicates: BM, C-n.v., L-n.v., S-n.v., U-n.v., US; fragm. MO; photo MICH ex BM).

Description: Leaves to 4 m long; scales of petiole bases 1-2 × ca. 0.1 cm, linear, sparingly denticulate (nearly entire), light brown; laminae 1-2 m long, 4-pinnate at base, 3-pinnate-pinnatifid medially; basal pinnae ca. 1 m long, strongly inequilateral, pinnules acroscopically reduced toward bases of pinnae; pinna rachises abaxially glandular with sessile to short-stalked glandular hairs, adaxially pubescent and glandular, hairs 0.1-0.3 mm long, 1-3 celled; costules on abaxial surfaces sparsely scaly, scales 0.5-0.7 mm long, light brown, ovate-lanceolate, non-bullate, pubescent, hairs ca. 0.1-0.2 mm long, with many gland-tipped hairs (more so than on tissue between veins), glandular cell yellowish pubescent, hairs on adaxial surfaces 0.3-0.4 mm long, 3- or 4-celled; laminar tissue between veins densely and evenly puberulent on both surfaces; hairs on abaxial surfaces ca. 0.1 mm long, erect, 1-celled, some of the hairs gland-tipped, glandular cell yellowish, spherical, sometimes sessile or nearly so; hairs adaxially on tissue between veins, ca. 0.2 mm long, 1-celled, glandular hairs sparse; veins visible, pubescent on both surfaces, hairs abaxially ca. 0.3 mm long, 2-celled, hairs adaxially sparser, ca. 0.5 mm long, 3- or 4-celled; lamina margins ciliate, hairs 0.2-0.3 mm long, 1-celled, glandular hairs sparse to absent; indusia < 0. 3 mm, fugacious and usually seemingly absent, glandular and pubescent, hairs sometimes appearing mixed among the sporangia.

Distribution: Brazil, Argentina; 500-850 m.

Comments: Megalastrum adenopteris is characterized by dense even uniform, erect hairs on the abaxial surfaces of the laminae, glands on both surfaces of the laminae, costae, and costules, and minute fugacious indusia. Glands are usually most evident on the costae and costules abaxially, either sessile or with a one-celled stalk. Unlike most Megalastrum in the region, the rachis scales are widely spreading. The indusia are often apparently absent, or they appear as a cluster of several minute (ca. 0.05 mm long) scales. Whether this condition is homologous with true indusia is uncertain. The most similar species is Megalastum umbrinum, which differs by laminae glabrous adaxially between the veins (or with a few hairs near the margin), rachis scales appressed, and lack of minute fugacious indusia. Megalastrum abundans differs by numerous bullate scales on the costae and costules abaxially, sparser pubescence of the laminae abaxially, absence of glandular hairs, and lack of indusia. Megalastrum crenulans differs by persistence large indusia, the hairs between the veins abaxially all short (ca. 0.1 mm long) glandular, and hairs on the adaxial surfaces of the costules 0.5-0.7 mm long, 5- or 6-celled.

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