Rhapis laosensis Beccari (1910: 225)

Henderson, Andrew, 2016, A revision of Rhapis (Arecaceae), Phytotaxa 258 (2), pp. 137-152 : 144

6. Rhapis laosensis Beccari (1910: 225) . Lectotype (designated by Hastings 2003):— LAOS. Saraburi, no date, C. Thorel 3154 (lectotype P!, isolectotype FI!)

Stems 2.2(1.0–3.2) m long, 0.7(0.4–1.0) cm diameter. Leaf ligules lobed, more or less persistent; petioles 34.3(7.5– 69.5) cm long, 2.6(1.6–3.9) mm wide at the apex; abaxial hastula usually complete, a low ridge separating petiole apex from costa; segments 8(2–13) per leaf; central segments lanceolate or elliptic, usually multi-veined, acuminate, the apices oblique, toothed, 29.3(18.5–41.0) cm long, 3.7(1.5–7.0) cm wide at midpoint, joined at the base, the non-split basal part 4.1(1.6–8.8) cm; lateral segments 26.8(15.0–39.0) cm long, 2.4(1.0–4.3) cm wide at midpoint, the non-split basal part 2.2(1.0–5.4) cm; abaxial surface of segments without scales, not indumentose when first exposed. Inflorescences small to large, with the first branch almost as large as the rest of the inflorescence; prophyll and peduncular bract broad, flattened, completely overlapping, the inflorescences exerted laterally through the bracts on a recurved peduncle; rachis 8.1(5.4–14.0) cm long; rachillae not filiform, glabrous; proximal rachilla 6.0(3.8–10.2) cm long, 1.3(0.8–2.6) mm wide; staminate and pistillate flowers sessile; staminate and pistillate corollas with poorly developed, inturned apical lobes, these not swollen internally; filaments terete; fruits globose, white, 8.3(7.2–9.7) mm long, 6.7(5.5–7.8) mm diameter, borne on a swollen, persistent perianth.

Taxonomic notes:— Hastings (2003) reported one specimen as having hermaphrodite flowers (see also Giddey et al. 2009).

Subspecific variation:—The range of Rhapis laosensis is divided into two lowland populations — west ( Laos, Thailand) and east ( Vietnam) of the higher elevation Truong Son range. Specimens from Laos and Thailand differ significantly from those from Vietnam in ten variables (stem diameter, petiole length, petiole width, number of segments, length of central segment, non-split part of central segment, length of lateral segment, non-split part of lateral segment, rachis length, proximal rachilla length)(t -test, P <0.05), with specimens from Vietnam having higher mean values for all variables. Based this, the two populations are recognized as subspecies (subspp. laosensis , macrantha ).