Monographs Details: Disterigma leucanthum A.C.Sm.
Authority: Pedraza-Peñalosa, Paola. 2010. (Ericaceae, Vaccinieae). Fl. Neotrop. Monogr. 108: 1-126. (Published by NYBG Press)
Family:Ericaceae
Description:Species Description - Epiphytic shrubs. Young branchlets ridged, ± smooth, glabrate, the hairs inconspicuous, eglandular, white, the mature branches glabrous. Leaves 0–2 per cm, spirally arranged, diffuse or patent; petiole 1.5–2.2 mm long, glabrate, the hairs inconspicuous, eglandular; lamina ovate or elliptic, 1.2–2.8 × 0.7–1.6 cm, basally obtuse, marginally entire, slightly revolute, apically ciliolate with minute eglandular hairs, apically obtuse or acute, adaxially glabrous or glabrate with inconspicuous eglandular hairs over the midvein, abaxially glabrate with glandular hairs, the venation adaxially 3- or 5-nerved with the midvein impressed or raised, abaxially hyphodromous with the midvein raised. Axillary solitary flowers and rarely 2-flowered fascicles; bracts 5–7, chartaceous, ovate, 0.7–1.5 × 0.9–1.4 mm, marginally ciliolate with inconspicuous eglandular hairs, apically obtuse, abaxially glabrate with inconspicuous eglandular hairs; pedicel 1.7–3 mm long, evident or at least with a portion not completely obscured by overlapping bracts, puberulous with eglandular and glandular hairs; differentiated apical bracteoles 2, distinct, chartaceous, enveloping entire calyx tube, covering 30–47% of calyx, obovate or transverse-elliptic, 1.5–2 × 2.6–4 mm, marginally ciliate with eglandular or glandular hairs, apically truncate (less often subtruncate), the surface slightly pustulate, abaxially densely puberulous or glabrate in cultivation, the hairs eglandular, adaxially glabrous. Flowers 4-merous. Calyx aestivation imbricate, campanulate, (3.5–)4.2–6.5 mm long; tube angled, 1.2–2.5 mm long, abaxially densely puberulous or glabrate in cultivation, the hairs eglandular; limb (2–)3–4 mm long, abaxially densely puberulous or glabrate with eglandular hairs, adaxially glabrate with minute eglandular hairs; lobes ovate, (2–)2.5–3.8(–4.5) × (1.5–)2– 3.2(–3.5) mm, marginally ciliate with eglandular hairs, apically acute; sinuses obscured by the overlapping bases of the imbricate lobes (sometimes pressing makes the lobes spread). Corolla pink or white, thick-fleshy, bistratose, urceolate, (5.5–)6–9 mm long, 3.7 mm diam. (1.8–2.3 mm when dry), 3 mm wide at throat (1.5–2.3 mm when dry), abaxially densely puberulous (especially distally) or glabrate in cultivation, the hairs eglandular or glandular, adaxially glabrate at least on the lobes; lobes 0.9–2 × 0.8–1.3 mm, apically acute, adaxially rugose. Stamens 8, (4.5–)5.8–6.4 mm long, exserted or included; filaments distinct, straight, ± linear with parallel sides, 2.2–3 mm long, abaxially glabrous or glabrate in cultivation, adaxially puberulous distally; anthers distinct, papillae only on thecae, some with few hairs at base; thecae (1.3–)1.7–2 mm long, without basal appendages; tubules 2, distinct, 1.9–2.6 mm long, dehiscing introrsely by longitudinal slits, 0.6–0.7 mm long. Ovary 4-locular; style (5–)6.3– 9.7 mm long, exserted. Berry unknown.

Distribution and Ecology - Disterigma leucanthum is a rare species known from very few collections from Cordillera Cutucú and Cordillera del Cóndor, Prov. Morona-Santiago, in eastern Ecuador (Fig. 31). This species grows in premontane cloud forests at 1000–1800 m, apparently on sandy soils. Flowering in Sep, Nov, and Dec.

Conservation Status - Disterigma leucanthum is known from few collections with a relatively restricted distribution area in eastern Ecuador. It was not until 2005 that new collections were added to the last known from 1976; in 2003, a living collection was known to be at the Royal Botanic Garden Edinburgh. Disterigma leucanthum is threatened by logging and colonization, and in the IUCN red list of plants endemic to Ecuador it is categorized as VU D2 (Pedraza- Peñalosa et al., in press).

Discussion:

The type collection of Disterigma leucanthum has distinctive flowers with the calyces and corollas densely puberulous abaxially; the imbricate calyx aestivation with the sinuses obscured by the overlapping bases of the imbricate lobes (sometimes the lobes spread during the pressing of the specimens); the calyx lobes ovate and adaxially glabrate; and the corolla adaxially glabrate. Also characteristic of the species is the pedicel evident or at least with a portion of it not completely obscured by the overlapping bracts, and the minutely pustulate surface of the differentiated apical bracteoles. The floral indumentum of some collections, including the specimens from cultivated plants (Argent C12880, C12881; Cubey 2), is glabrate instead of puberulous; unfortunately, because the herbarium specimens of this species are so few, it is not possible to discern which represents the typical condition. Additional collections from Los Tayos, Argent C12880 (E), and from Valle del Río Pastaza near El Topo, Camp E-1684-5 (NY, US) and Camp E-2410 (NY) differ from the typical D. leucanthum in not having calyx lobes overlapping so strongly. Collections from Huila, Colombia, Luteyn 4966 (COL, L, NY) and Lozano 4145 (COL, WIS), could belong here or to a new species, but unfortunately, the flowering material is inadequate to justify any decision on such a disjunct population.

Distribution:Ecuador South America| Morona-Santiago Ecuador South America|