Rhapis subtilis Beccari (1910: 227)

Henderson, Andrew, 2016, A revision of Rhapis (Arecaceae), Phytotaxa 258 (2), pp. 137-152 : 149

10. Rhapis subtilis Beccari (1910: 227) . Type:— LAOS. Lakon, 1866–1868, C. Thorel 3099 (holotype P!, isotype FI!)

Stems 2.1(1.3–2.5) m long, 0.6(0.3–1.0) cm diameter. Leaf ligules lobed, more or less persistent; petioles 28.6(7.0– 52.5) cm long, 1.9(1.1–2.8) mm wide at the apex; abaxial hastula usually incomplete, part of the petiole continuous with the costa, sometimes complete, a low ridge separating petiole apex from costa; segments 7(2–11) per leaf; central segments lanceolate or elliptic, usually multi-veined, acuminate, the apices oblique, toothed, 22.3(9.0–33.0) cm long, 2.9(1.2–7.0) cm wide at midpoint, free almost to the base or sometimes joined at the base, the non-split basal part 2.0(0.2–6.0) cm; lateral segments 20.4(8.2–29.0) cm long, 1.6(0.6–3.8) cm wide at midpoint, the non-split basal part 1.3(0.3–2.7) cm; abaxial surface of segments without scales, not indumentose when first exposed. Inflorescences slender, few branched, with the first branch not as large as the rest of the inflorescence; prophyll and peduncular bract narrow, tubular, not or scarcely overlapping, the inflorescences exerted apically through the bracts on a curved peduncle; rachis 4.5(1.0–12.8) cm long; rachillae not filiform, glabrous; proximal rachilla 9.8(2.8–15.5) cm long, 1.2(0.7–2.0) mm wide; staminate and pistillate flowers sessile; staminate and pistillate corollas with well developed, erect, triangular apical lobes, these swollen internally; filaments terete; fruits globose, white, 7.5(6.0–9.4) mm long, 6.1(5.6–7.1) mm diameter, borne on swollen, persistent perianth.

Taxonomic notes:— Two qualitative variables (abaxial hastula and central segment splitting) were found to be polymorphic within Rhapis subtilis (as a preliminary species). However, splitting the preliminary species into several consistent species, as described in the Materials and Methods section, was found to give improbable results, and no corroborating evidence that these were separate taxa was found (no geographic separation, no quantitative differences). Therefore, R. subtilis is recognized as a phylogenetic species with two variables treated as traits.

Subspecific variation:—Specimens of Rhapis subtilis come from two separate areas—a southern one in Peninsular Thailand and a northern one in south-central Thailand, central Laos, and western Cambodia. Specimens from the southern area differ from those from the northern one in eight quantitative variables (stem diameter, petiole length, number of segments, length of central segment, non-split part of central segment, length of lateral segment, rachis length, proximal rachilla length)(t -test, P <0.05), with specimens from the southern area having higher mean values for all variables. Based on this, the two are recognized as subspecies (subspp. siamensis , subtilis ). Lacking enough data for testing, the two, incomplete specimens from Sumatra are included in subsp. siamensis .