Leucoloma crosbyi (Dicranaceae), a New Species Endemic to Northern Madagascar

Abstract

Leucoloma crosbyi, a new species from northern Madagascar, is described, resulting from a revision of the pantropical genus. Diagnostic characters include: robust habit; narrow, opaque, juxtacostal bands tapering to basal region; costal-laminal transition zone with 2-9 multito bistratose rows; interior cells forming broad scarious region; narrow hyaline margin; and longitudinally thickwalled alar cells. It is most closely related to L. grandidieri Ren. & Card. and has been confused with L. talazaccii Ren. & Card. Ferdinand Renauld published Essai sur les Leucolomas in 1909, the first and only comprehensive treatment of Leucoloma, enumerating 131 species for the world. Renauld & Cardot (1915) produced Les Mousses de Madagascar, which described 38 species of Leucoloma for Madagascar. Crosby et al. (1983) listed 51 species for Madagascar and nearby islands, based on available literature. From current revisionary work on the genus, collections from Montagne d'Ambre by Crosby in 1972 have resulted in the description of a distinct taxon, Leucoloma crosbyi LaFarge-England. Leucoloma is a large pantropical genus that has a strong center of diversity in the rainforests of east Africa, Madagascar, and surrounding islands. Specific endemism for this region is 94 percent. The revision of the genus is expected to modify this figure, though rates of endemism should remain high for this region. The species described below supports this view. Leucoloma crosbyi LaFarge-England, sp. nov. TYPE: Madagascar. Diego Suarez: Montagne d'Ambre, Parc National, 10 km along trail between Petit Lac and Grand Lac, 12?34'S, 49?12'E, 13 Nov. 1972, 1,200 m, Crosby & Crosby 7167 (holotype, MO; isotype, ALTA). Figures 1-12. Dioicous. Plantae robustae, pallide vel glauco-virides ad 5 cm altae. Folia longa et flexuosa. Cellulae juxtacostales papillosae densissimae obscurae in vittis utrinque /5 distalis costae latere dispositae. Latibasis scariosa sensim angustata versus marginem hyalinam. Cellulae alares planae, rufo-fuscae, scalariformes. Setae 1.0-2.0 mm longae. Capsulae 0.9-1.5 mm longae, ovales ad oblongae, erectae, immersae. Dentes peristomii quasi ad basim divisi. Calyptrae mitratae. Species haec ab Leucoloma grandidieri Ren. et Card. differt vix rugosis laminis et foliis longioribus, costa latiore et vittis cellularum juxtacostalium papillosarum versus basim angustioribus. Dioicous. Plants robust, erect to spreading, pale to glaucous green or tan to light-brown, forming loose tufts up to 5 cm tall. Stems red, nontomentous, elliptic in transverse section (0.36-0.32 mm long by 0.31-0.24 mm wide), central strand lacking, outer 3-5 layers of red-brown, thick-walled cortical cells with smaller lumen than the homogenous inner, yellow to tan walled cortical cells; stems densely leave , unbranched or sympodially branched, fertile branches distally ramulose from subapical innovations below perichaetia or perigonia, 1 to several. Rhizoids smooth, red-brown, several to numerous at the base of stem or potentially deciduous branches encircling supporting axis. Juvenile leaves 0.3-3.0 mm long, ovate to ovate-lanceolate, apices shortly acu inate to acuminate, at base of each branch and stem. Leaves erect to wide spreading wet or dry, 4.0-6.5 mm long, 0.2-1.2 mm wide, narrowly ovatelanceolate to lanceolate, plane to slightly concave below, not to slightly transversely rugose in medial region, tapering gradually to a long, subulate, subtubulous, nonrugose acumen; apices flexuose to slightly incurved when dry. Mean acumina to shoulde , shoulder to base ratio is 1: 1.65. Margins plane, entire, with a distinct, narrow, hyaline border ranging from 1 to 2 cells at the base of the leaf, reaching a maximum width of 3-6 cells (9.6-16.8 Aum wide) in the median region of the leaf, narrowing to a single cell in the upper region and ending below the apex; apex rounded or acute, serrulate to multiserrate. Costa 52.8-106.0 gum wide at base, subpercurrent, ending 3-6 cells below the apex, shiny, translucent; transverse section plano-convex to elliptic, 24.0-33.6 ,m diam., with abaxial and adaxial stereids in 3-5 rows, guide cells 4-6 in a single row, sometimes double. Juxtacostal cells 4.8-12.0 Aim long, 4.8-7.2 ,m wide, irregularly quadrate NOVON 2: 119-122. 1992. This content downloaded from 207.46.13.11 on Tue, 18 Oct 2016 05:56:39 UTC All use subject to http://about.jstor.org/terms