Similar to Ch. tonkinensis by its inflorescence appearing at the base of the leafy shoots, but differs by its unbranched or very sparsely branched stems, densely puberulent leaf sheaths, densely puberulous lower side of lamina and cream-white flowers (compared to densely branched stems, glabrous leaf sheaths, glabrous lamina on both sides and yellow flowers with red markings on basal part of the labellum).

Figure 3. 

Cheilocostus candidus Škorničk., Böhmová & H.Ð.Trần sp. nov. A habit B leaves C detail of young stem with pulvini and bases of leaf blades D detail of young and old stems covered with leaf sheaths E detail of lower surface of the leaf blade. Based on plant used to prepare the type specimen Leong-Škorničková GRC-421, photo by Jana Leong-Škorničková.

Collected from the material cultivated at the Singapore Botanic Gardens, 21 September 2021, Leong-Škorničková GRC-421 (holotype SING (inclusive flowering material in spirit), isotypes E, P, SGN). Originally collected from Vietnam, Lâm Đồng Prov., 20 June 2008, Trần et al. 54 (living material only).

Terrestrial, perennial herb in loose small clumps to ca. 2 m tall; stems up to 2.5 cm in diam. at base, unbranched or barely branched (in stems where the apical part was damaged) with 15–35 leaves, leafless in lower third; sheaths green, puberulent, becoming brown and papery with age; ligule 1–2 mm long, irregularly truncate, pale green, becoming pale brown with age, puberulous; petiole 2–5 mm long, pale green, bluntly canaliculate (kidney-shaped in cross-section), pubescent; lamina weakly obovate to elliptic with round to obtuse, slightly unequal base and acuminate apex, 12–28 × 4–11 cm, weakly plicate, somewhat thick, adaxially mid-green, glabrous, abaxially paler green, puberulous. Inflorescence radical, on a separate leafless shoot emerging directly from the rhizome; peduncle horizontal to ascending, 3–12 cm long, sheaths ± tubular, green, turning brown with age, densely pubescent, margin irregular; spike ovoid to narrowly ovoid, up to 20 cm long, 4.5–8 cm wide (narrower in very young, widening as the flowering progresses), composed of up to ca. 120 imbricate bracts, arranged in right-handed spiral, each supporting a single bracteole and single flower (lowermost 5–10 sterile), 1–2 flowers per inflorescence open at a time; fertile bracts ovate to broadly ovate, to 3.2–5.5 × 2.5–3.5 cm, cream at base, light green distally, softly pubescent externally, glabrous internally, apex ending in very sharp callus, callus 6–7 mm long, glabrous; bracteole 3–4 × 0.9–1.2 cm long, unequally folded with single sharp keel, white to cream at base, pale green distally, externally softly pubescent, internally glabrous, apex acuminate with very sharp callus, callus ca. 5–7 mm long. Flower 9–11 cm long, exserted 5.5–7 cm above the supporting bract; calyx 3.5–4 cm long, cream to pale beige at base, light green distally, densely pubescent, apex 3-lobed, lobes 5–10 mm long, ending with very sharply mucronate callus, each callus ca. 4–5 mm long, glabrous; floral tube (measured from the apex of ovary to the point of divergence of corolla lobes) 2–2.5 cm long, fused solid with style in basal ½, white to cream, externally and internally glabrous; staminal tube (measured from the point of divergence of corolla lobes to the point of divergence of stamen form the labellum) 8–11 mm long, white to cream, externally glabrous or with sparse hair, internally with long glandular hair; corolla lobes unequal, translucent cream-white, densely pubescent externally, glabrous internally, apex mucronate, mucro to 2–5 mm long, dorsal lobe obovate, symmetric, 5.1– 5.8 × 1.9–2.2 cm, lateral lobes unequal in width, asymmetrically obovate, 4.8–5.2 × 1.7–2 cm; labellum 5.5–6 cm long, ca. 7–8 cm broad (when flattened), broadly obovate with apex often bilobed (lobes overlapping), thickened in the centre, thin towards the margins, cream white to very pale yellow in the central part, adaxially with glandular hair (more dense in central part, nearly glabrous towards the margins), abaxially mostly glabrous with some glandular hairs, margin crisped, with glandular hair; stamen petaloid, slightly obovate, ca. 2.6 cm long (ca. 3 cm with crest flattened), ca. 6 mm wide at base, ca.1.3 cm wide at widest point, white to cream-white with pale yellow crest, adaxially glabrous, abaxially with sparse long glandular hair, crest 3–4 mm long, ca. 10 mm wide at base, rounded to obtuse, recurved, with glandular hair at margin; thecae 9–10 mm long, 3–4 mm across (both), dehiscing throughout their entire length. Ovary barrel-shaped, 13–16 × 10 mm, cream covered with soft dense beige hair, somewhat flattened and irregularly triangular in cross-section, trilocular with central placentation and apically embedded cream to beige coloured gynopleural nectaries, each locule with many ovules; style ca. 4 cm long (free part), white, glabrous; stigma semi-circular, 2 mm long, ca. 4 mm wide, dorso-ventrally flattened, 2-lamellate with dorsal 2-lobed appendage, cream white. Fruits and seeds not seen.

The specific epithet refers to the white colour of the flower.

Endemic to Vietnam.

This species occurs near rocky streams in lowland broadleaved evergreen forest, at elevations about 200–300 m. Flowering in the field was observed in June, in cultivation, it extends to October; fruiting has not been so far observed.

The species is, so far, known only from the type locality, where only a few individuals were seen. A suitable habitat exists in the proximity of the type locality and it is, therefore, most likely that the species has a wider area of distribution as it is highly unusual for Costaceae species to be stenoendemic. Nevertheless, as there is no reliable information on the population sizes or distribution of this species, we propose to treat it currently as Data Deficient (IUCN 2019).

Cheilocostus candidus is similar to Ch. tonkinensis in producing the inflorescence radically. It is, however, fairly easy to recognise it in the field even in sterile conditions by its barely branched leafy shoots, which have densely puberulent leaf sheaths and densely puberulous lower surface of lamina, compared to multi-branched stems and always glabrous leaves of Ch. tonkinensis.

Axillary branching of the leafy stems has been mentioned as one of the generic descriptions of Cheilocostus by Specht and Stevenson (2006). Since then, Ch. borneensis A.D. Poulsen, a species that does not have axillary branching has been described (Poulsen and Specht 2010)). Cheilocostus candidus also does not branch or branches very sparsely (usually only after extensive damage of the main shoot by herbivory or cutting), which is yet another character helpful in the field.

No other specimens of this species were found in E, HN, K, P, SING, and VNM.

The type locality of Cheilocostus tonkinensis is in northern Vietnam, Mount Ba Vì. In the protologue, Gagnepain (1902) refers to two collections made by Balansa from this locality. There are four sheets at P: a single sheet of Balansa s.n., collected on 24 July 1886 [P00686610 – inflorescences & flower] and three sheets of Balansa 4206 collected in October 1887 [P02198384 – leafy shoot & single fruit; P02198381-inflorescence only; P02198385-leafy shoot only]. Both of these collections predate the protologue and are annotated in Gagnepain’s hand as published in Bull. Bot Soc. France 49: 248. All four sheets have to be considered as syntypes and, therefore, the lectotypification is needed. Unfortunately, none of the specimens consists of both leafy shoot and an inflorescence. Balansa s.n. [P00686610] with inflorescence and a flower, accompanied by a pencil drawing, is selected here as the lectotype.

It is challenging to distinguish Asian radically flowering Costaceae in herbarium material as the flowers do not preserve well. Based on our observations of living flowering material and photographic records with location data, Cheilocostus tonkinensis, so far, occurs in S. China, northern and central Vietnam and northern Laos, but may possibly extend to Thailand.