A Taxonomic Revision of Mezoneuron (Leguminosae: Caesalpinioideae: Caesalpinieae) Author Clark, Ruth P. text Phytotaxa 2016 2016-09-14 274 1 448 450 http://dx.doi.org/10.11646/phytotaxa.274.1.1 journal article 10.11646/phytotaxa.274.1.1 1179-3163 13657001 12. Mezoneuron pubescens Desfontaines Mem. Mus. Hist. Nat. Paris 4: 245. 1818 . Holotype :— JAVA , Leschenault s.n., P (P 02142683 !) Synonym. Caesalpinia pubescens (Desf.) Hattink. Reinwardtia 9(1): 47. 1974 . Mezoneuron pubescens Desf. var. longipes Craib. Fl. Siam . Enum. 1: 500. 1928. Holotype :— THAILAND , Surat , Kanchanandit , Aug. 1927 , Kerr 13111 , K (K000264758!). Synonym. Mezoneuron glabrum Desf. Mem. Mus. Hist. Nat. Paris 4: 245. 1818 . Holotype :—TIMOR, Leschenault s.n., P (P00293980!). Synonym. Mezoneuron intermedium Zippelius ex Spanoghe. Linnaea 15: 200. 1841 . Woody climber, or scandent shrub, to 4 m tall and spreading to 15 m . Stems sometimes with small, scattered recurved prickles; sparsely to moderately whitish to orange tomentose. Stipules caducous, triangular, 1.5–5 mm long, subglabrous to densely golden tomentose. Leaves with 7–15 (–18) pairs pinnae; 5–11 pairs leaflets per pinna; petiole 2–7.8 cm ; leaf rhachis (9–) 15–34 [–50] cm, with recurved prickles on leaf rhachis in pairs or threes at the pinna insertion points, and usually scattered on the internodes, a single prickle at apex of rhachis, ca. 2 mm long; pinnae 2–8.5 cm ; leaf rhachis, petiole, and pinna rhachis sparsely to moderately whitish to orange tomentose. Leaflets alternate to opposite, often discolorous, darker above; the terminal leaflets obovate, base oblique, apex rounded to slightly acute, mucronulate, (5–) 10–20 × 3–13 mm , lateral leaflets oblong, base oblique, midvein often excentric to almost diagonal, 5–20 × 2–13 mm ; upper surface of all leaflets sparsely to moderately appressed tomentose, occasionally glabrous, lower surface sparsely appressed tomentose, often denser on midvein and margins, the hairs pale orange to golden to whitish; 2˚ venation anastomosing, 3˚ venation reticulate, veins clearly A TAXONOMIC REVISION OF MEZONEURON Phytotaxa 274 (1) © 2016 Magnolia Press • 23 visible on lower surface, faintly visible above. Inflorescence a raceme or few-branched panicle, terminal or (supra-) axillary, to 40 cm , sparsely to moderately whitish or golden or orange tomentose on all parts, the hairs often denser and darker in colour on calyces and younger parts; occasionally small recurved prickles on the basal ⅓ of infloresence rhachis; pedicels 14–40 mm , articulated 1–3 mm below the hypanthium. Bracts sometimes present, lanceolate to triangular, 1–4 × 1 mm , moderately tomentose; bracteoles semi-persistent, lanceolate or elliptic, long-acuminate, 6–15 mm × 1–3 mm , orange tomentose on both surfaces, the hairs forming a distinct central longitudinal stripe on the outer surface. Flower with a hypanthium 2–4 mm × (6–) 7–8 mm ; lower calyx lobe 12–17 × 6–12 mm , other lobes broad, rounded, 8–11 × 5–7 mm , hypanthium and calyx lobes all moderately to densely orange pubescent on both surfaces. Median petal strongly reflexed backwards, with a pronounced transverse flap of tissue on the inner surface between claw and blade; 8–14 mm long, blade oblong to suborbicular, 4–8 × 5–11 mm , glabrous or with a few hairs on outer surface, claw 4–6 × 0.5–2.5 mm , glabrous or with a few hairs on outer surface. Upper lateral petals obovate to suborbicular, blade 9–14 [–20] × 8–16 [–20] mm, claw 2–3 mm long, few hairs at the base of claw on inner and outer surfaces, occasionally glabrous. Lower laterals obovate to suborbicular, blade 8–13 [–20] × 8–14 [–20] mm, claw 2–3 mm long, few hairs at the base of claw on inner and outer surfaces, occasionally glabrous. Stamen filaments flattened, (12–) 14–18 mm long, the filament of vexillary stamen glabrous, the other filaments covered with dense villous orange hairs on the basal ½, along the inner surface; anther ca. 2.5–3.5 mm . Ovary 5–8 mm long, style [3–] 8–13 mm long, the ovary and basal ⅓ of style moderately to densely orange sericeous, sometimes extending the length of the style; stigma funnel-shaped, ca. 0.5–1 mm wide, the rim papillate. Fruit narrowly elliptic, sometimes slightly falcate, base sometimes oblique, apex acute, the central nerve extending to form a slight beak, the persistent, asymmetric hypanthium wider below winged side of fruit; 8.5–24.5 × 3–5.5 cm , the wing arising basally up to 12 mm along central nerve, wing 8–20 mm wide; fruit surface densely orange tomentose when young, hairs usually becoming sparse when mature, glabrescent, venation reticulate, raised and visible on fruit body, anastomosing and slightly visible on the wing; hypanthium semi-persistent. Seeds 4–9 per fruit; arranged close together, adjacent to and perpendicular to the central vein, not visible in outline on fruit exterior, outline of entire seed chamber sometimes slightly visible; ellipsoid, 8–10 × 3–6 mm , brown, smooth. FIGURE 13. Distribution of M. pubescens in South East Asia. Distribution :— Thailand , Laos , Vietnam , Indonesia , Lesser Sunda Islands , Philippines , Java, Sumatra, Sulawesi. ( Fig. 13 ). Habitat and ecology :—Scrub, dry thicket, savannah, monsoon forest. Elevation to 700m . Occurs in regions that experience a dry season. Phenology :— Thailand , Vietnam : flowering March–October, fruiting March–November. Malesia : Flowering March–October, fruiting May–January. 24 • Phytotaxa 274 (1) © 2016 Magnolia Press CLARK Preliminary conservation assessment :—Extent of Occurrence 7,038,070.582 km 2 = LC; Area of Occupancy 96.000 km 2 = EN. Category assigned:— Least Concern (LC). However, the majority of the existing herbarium specimens were collected before 1950, and the most recently collected specimen known to the author is from 1980. This suggests that the species distribution may have been reduced since the majority of the specimens were collected, and is smaller than the specimen data appears to show. If further data becomes available, it is likely that a higher category of threat will be assigned to this species.