Sarcolobus cambogensis McHone and Livsh., 2015

Mchone, Elizabeth E., Won, Hyosig & Livshultz, Tatyana, 2015, Sarcolobus cambogensis (Marsdenieae, Asclepiadoideae, Apocynaceae): A new rheophytic shrub from Cambodia, Phytotaxa 197 (1), pp. 45-53 : 48

Sarcolobus cambogensis McHone and Livsh. sp. nov. ( Figs. 1–4 )

Similar to Sarcolobus borneensis (van Steenis) P.I.Forst. and Sarcolobus luzonensis (Warb.) P.I.Forst. in shrubby, rheophytic habit and narrow leaves, distinguished from them by its comparatively broader leaves, prominent staminal coronas, and wider caudicles.

Type: — CAMBODIA. Koh Kong: ca. 6 km SW from the Central Cardamom Protected Forest Thmor Bang Station, 11°39’39.2”N 103°23’58.5”E, 342 m, 6 January 2012, H. Won et al. 6398 (holotype PH!; isotypes DGU!, KB!) .

Plant s erect rheophytic shrub to 60 cm high. Latex white. Stems woody, terete, 3–6 mm in diameter, slightly tomentulose, glabrescent; internodes up to 15 mm long. Stipular colleters paired, on opposite edges of petiole base, ca. 300 × 200 μm, triangular, senescent. Leaves opposite, petiolate; petiole 3–10 × 0.6–1.4 mm; lamina linear-lanceolate, 33–87 × 5–13 mm, discolorous, glabrescent, margins weakly revolute and weakly undulate; adaxial surface medium to dark green, venation obscure, with 1–2 laminar colleters at base, ca. 400 × 200 μm, triangular, senescent; abaxial surface pale green, venation visible, pinnate, 12–16 secondary vein pairs diverging at a ca. 45° angle to the primary vein, brochidodromous; apex weakly apiculate, base attenuate. Inflorescence terminal, appearing axillary when overtopped by axillary shoot, umbelliform (early) to racemiform (late) cymes up to 45 mm long with up to 8–10 flowers at apex, lower portion of older rachises with a spiral of pedicel scars and persistent subtending bracts; unbranched or rarely two-branched; bracts triangular, 0.9–2.3 × 0.4–1.2 mm, with sparse indumentum, lower-most bract slightly larger, ca. 3 mm below the phylotactic spiral; peduncle 4–9.7 × 1.2–2.1 mm. Flowers 3.7–6.6 × 4.7–9.5 mm, subtended by paired bracts, pedicels 5–6.5 × 0.6–1.3 mm, with scattered indumentum; sepals 5, imbricate, lanceolate, basally connate, 1.6– 3.4 × 1.5–2.3 mm; colleters 5–11, in sinuses of sepals (rarely opposite sepals), 1–4 in each sinus, 200–400 × 80–250 μm. Corolla subrotate to campanulate, orange to yellow-orange, glabrous except for sparse indumentum on adaxial petal tips; tube 1.9–3 × 3.3–6.5 mm; lobes lanceolate, 2–3.8 × 0.9–3.2 mm, contorted to the right in bud; corolline corona absent. Gynostegium yellow, glabrous, conic, 3.3–3.6 × 2.3–3.8 mm, sessile, apex truncate. Anthers oblong, 1.5–1.7 × 0.3–0.5 mm; apical connective appendages triangular, hyaline, 0.5–0.8 × 0.5–0.7 mm, apex obtuse; guide rails 1.3–2 × 0.6–1 mm, basally divergent. Staminal corona of 5 prominent lobes attached near base of gynostegium, lobes A-frame shaped, triangular in longitudinal section, basally sulcate, 1.3–2 × 0.6–1 mm. Pollinaria 440–570 × ca.600 μm; corpusculum oblong, brown, deep fissure running the length, 380–420 × 130–190 μm; caudicles yellowgreen, flattened, 130–230 × 60–150 μm, weakly geniculate; pollinia ellipsoid, 260–390 × 170–250 μm. Gynoecium superior, stylehead turbinate, 5-angled, ca. 2.3 × 2.4 mm, apex truncate, not papillate, ovaries ca. 1.5 mm long. Fruit pedicel 6–18 × 2–5 mm; follicles fusiform, abruptly narrowed at the base, upright, solitary or paired on each pedicel, brown at maturity, striate, ca. 40 × 4–11 mm. Seed ovate (almost trullate), with flattened margins, brown, 3.9–6.3 × 1.9–3.2 mm; coma white, wispy, 8–13.9 mm long.

Phenology: — Flowers present December–February; fruits present November–February and May.

Distribution: —Tatai River, Koh Kong province, Cambodia.

Ecology: —A rheophyte of seasonally flooded stream and river channels, growing in sunny areas on sandy or rocky clay soils, often rooting among boulders, at 100–500 m elev. At the type locality the species is locally abundant, numbering ca. 200 shrubs, but absent to rare on nearby stretches of the river. The plants were growing around a flat rock basin that had been under ca. 0.5–1 m of water during the rainy season in August but completely exposed during the dry season in January. Plants were both flowering and fruiting. Scattered seeds with attached comas were floating at the margins of the water, indicative of dispersal by both wind and water.

Figures

FIGURE 1. Distribution of Sarcolobus cambogensis in Koh Kong province, Cambodia. Map generated with SimpleMappr (Shorthouse, 2010).

FIGURE 2. Sarcolobus cambogensis habitat and growth form. A. riparian habitat, B. shrubby habit, C. open follicle releasing seeds, and D. orange flowers (photographs: Hyosig Won from type locality)

FIGURE 3. Sarcolobus cambogensis. A. Habit. B. Stipular and laminar colleters. C. Follicular fruit. D. Seed, without coma. (illustrations: Elizabeth McHone, A from H. Won photograph at type locality, B from H. Won 6398, C from M. Newman 2337, and D from H. Won 8697)

FIGURE 4. Flowers of Sarcolobus cambogensis A. Side view of gynostegium: prominent staminal corona (cr), apically truncate gynostegium (gy). B. Top view of gynostegium. C. Side view of pollinarium: narrow-oblong corpusculum (cp), wide, barely geniculate caudicles (cu), pollinium (p). D. Top view of pollinarium. (illustrations: Elizabeth McHone from M. Newman 2162)