It differs from related species in its more numerous, regularly arranged lanceolate pinnae.

Type:— VIETNAM. Quang Ngai: Ba To District, road from Ba To to Ba Cung, steep slope in forest near road, 14°44’N, 108°53’E, ca. 600 m. 24 April 2013, A. Henderson & Nguyen Quoc Dung 3880 (holotype, VFM! isotype, NY!).

Stems clustered, 3–4 m long, 1–1.5 cm diameter with sheaths, 0.7 cm without sheaths. Sheaths densely brown tomentose initially, green, densely covered with greenish-yellow, flattened spines to 1.2 cm long; ocreas short, membranous, early deciduous; knees present; flagella present; petioles 18–44 cm long, spiny along the margins; rachises 45–50 cm long with 8–13, lanceolate pinnae per side, these regularly arranged, middle pinnae 28–31 cm long, 1.9–2 cm wide at widest point, minutely spiny along the margins, not spiny on the veins, apical pair joined for 8.5–8.7 cm. Staminate inflorescences to 150 cm long, flagellate; rachis bracts tubular, splitting near insertion of partial inflorescences or terminating just below them; partial inflorescences branched to 2 orders; rachillae 2–5.5 cm long; staminate flowers 4 mm long; sepals 2 mm long, tubular proximally, lobed distally; petals 4 mm long, valvate; pistillate inflorescences to 200 cm long, flagellate, branched to 1 order; rachis bracts tubular, terminating well below the partial inflorescences; rachillae 3–6 cm long; dyad bracteoles obscure, campanulate, one side of mouth acuminate, visibly ribbed, the base free from the preceding neuter flower and without an impression of its bracteole; pistillate flowers 3 mm long before anthesis; calyx 3 mm long, tubular, lobed at the apices; corolla 3 mm long, tubular, with 3, valvate lobes at the apices; fruits (immature) ellipsoid, 1.1 cm long, 0.76 cm diameter, 1-seeded; fruiting perianths tubular; endosperm homogeneous or scarcely ruminate; embryo basal.

Distribution and habitat:— Endemic to central Vietnam in Quang Ngai Province in secondary, evergreen forest at 600 m elevation.

Local names and uses:— may. The canes are used locally in furniture making.

Additional specimens examined:— VIETNAM. Quang Ngai: Ba To District, road from Ba To to Ba Cung, steep slope in forest near road, 14°44’N, 108°53’E, ca. 600 m, 18 July 2012, A. Henderson et al. 3811 (NY, VFM); same locality, 14 September 2011, Nguyen Quoc Dung 2035 (NY, VFM).

Discussion:— In Evans et al. ’s (2001a) treatment of Calamus in neighboring Laos, this palm will key to a group of clearly unrelated species; C. siamensis, C. tenuis Roxburgh (1832: 780), and C. godefroyi Beccari (1908: 267). In same study of Calamus cited under C. batoensis (Henderson, in prep.), Calamus quangngaiensis (named for the province in which it occurs) is placed as sister species to the clade including C. batoensis and related species. It differs from all of these in its more numerous, regularly arranged lanceolate pinnae.