A clump-forming, tall, water-loving, fast growing, dioecious, forest emergent, climbing palm. Not known in cultivation, rare in the wild. It has spiny, green stems, 7 m. (23 ft.) tall, 1.3 cm. (0.5 inch) diameter with no obvious leaf scars, and small segmented, palmate (fan) leaves, 0.9 m. (3 ft.) long, 0.6 m. (2 ft.) wide, light green above and beneath. Flagella present Cirri absent.
Calamus evansii naturally occurs in wet and humid tropical rainforest. In this type of natural environment temperature fluctuations are slight, and this palm prefers a constantly hot and humid climate with little temperature difference between day & night, and Summer & Winter. This palm will not tolerate cool for very long, and is one the most difficult palms to keep in cultivation.
Leaf sheaths green, with patchy, white tomentum initially, sparsely to densely covered with brown, black-tipped, flattened, horizontally spreading spines to 1 cm long, sometimes with many short spines interspersed; knees present; ocreas present, less than 0.5 cm long, densely covered with short, black bristles; flagella present; petioles 15-21 cm long, sparsely covered laterally and abaxially with recurved spines to 0.5 cm long; rachis 41-43 cm long, laterally and abaxially with few, recurved, solitary spines; pinnae 3-6 per side of rachis, lanceolate, arranged in distant groups or solitary, 30-43 cm long, 2.0-3.5 cm wide, without spines on the margins, minutely spiny at the apex, the apical pair of pinnae free or only briefly joined at their bases; cirri absent. Inflorescences 1.5-3 m long, flagellate; partial inflorescences inserted below the mouth of the partial inflorescence bracts; partial inflorescence bracts closely sheathing the main axis, briefly split at the apex, not bristly at the apex, densely covered with recurved spines; staminate inflorescences branched to three orders, with 5-7 partial inflorescences; rachillae 2-3 cm long; rachillae bracts distichously arranged, to 1 mm long, glabrous; floral bracteoles to 0.5 mm long, glabrous; staminate flowers not seen, arranged alternately and distichously along the rachillae; pistillate inflorescences branched to two orders, with 3-10 partial inflorescences, each with up to 19 rachillae; rachillae 3-8 cm long; rachillae bracts distichously arranged, to 2 mm long, glabrous; pistillate flowers to 12 per rachilla, borne alternately and distichously along the rachillae; sepals to 1.5 mm long, connate basally for ca. two-thirds their length, lobed above; petals to 2 mm long, free; fruits not seen.
Observation: Khammuane: Nakai District, Ban Malua, Phon Nong Na, 520 m.
Laos (Khammuane) lowland forest, at 520-530 m elevation.