Curcuma micrantha Škorničk. & Soonthornk., 2021

2. Curcuma micrantha Škorničk. & Soonthornk. View in CoL , sp. nov. (subg. Hitcheniopsis) — Fig. 2 View Fig

Similar to Curcuma parviflora Wall. in its small habit,inflorescence with distinct white coma bracts and flowers with purple labellum,but differs by fertile bracts supporting 4–6 flowers, flowers small and sunken into the subtending bract with labellum facing upwards and not reflexing out of the bract, and purple staminodes and filament (vs fertile bracts supporting 2 or 3 flowers, flowers with labellum reflexed out of the bracts, and white staminodes and filament in C. parviflora ). — Type: Sutthinut Soonthornkalump Sutt-214 (holo BKF, including flowers in spirit as part of a single specimen; iso QBG, SING, both including flowers in spirit as part of a single specimen), Thailand, Kamphaeng Phet Province, Phran Kratai District, Wang Khuang Subdistrict , c. 100 m elevation, 27 May 2020, flowering .

Etymology. The specific epithet is derived from Greek micro- = little, small and -anthos = flower: small flower.

Perennial rhizomatous herb, 25–60 cm tall. Rhizome globular to ovoid, 0.8–1.4 by 0.75–1.5 cm, occasionally with lateral branches 0.8–1 by c. 0.4 cm, externally yellowish white (young rhizome) to pale brown, covered with rusty coloured and decayed scales, internally cream-white, slightly aromatic with insipid taste; root tubers ovoid to fusiform, 1–1.9 by 0.8–1.5 cm, externally light brown, internally white. Leafy shoot with 3 or 4 leaves at anthesis; pseudostem up to 40 cm long, composed of 1 or 2 leafless sheaths and 3 and 4 leaf sheaths, green with reddish brown tinge basally, glabrous; ligule 1–2.5 mm long, bilobed, hyaline, greenish white, semi-translucent, glabrous except for a few hairs c. 0.1 mm long on upper margin; petiole 13–33 cm long, canaliculate, green, glabrous; lamina narrowly elliptic, (9.5–)12–27 by (2.5–) 4.5–7.8 cm, adaxially dark green, abaxially somewhat paler, glabrous on both sides, midrib green, margin hyaline, c. 0.1 mm wide, glabrous, base obtuse to oblique, apex acuminate to narrowly acuminate. Inflorescence central; peduncle exceeding pseudostem by 10–15 cm, light green (on exposed part), glabrous; thyrse 5–7.5 by 2.2–3 cm, composed of 8–13 fertile bracts and 2–9 coma bracts; coma bracts elliptic to ovate, 7–23 by 5–12 mm (basal large, uppermost smallest), apex acuminate, white with green tip, most often with pink to reddish tinge (degree of tinge varying from slight to heavy), glabrous on both sides except for a few hairs c. 0.1 mm long on abaxial side of apex; bracts broadly obovate, 13–17 by 15–18 mm, connate in basal 1/2, green with rich reddish brown tinge (rarely plain green), glabrous on both sides, apex broadly acute to obtuse, strongly reflexed; cincinni with up to 6 flowers at most basal bracts, the number gradually decreasing upwards; bracteoles triangular, 3–5 by 2.5–5 mm wide at base (outer ones largest), hyaline, semi-translucent white, glabrous (or rarely with a few hairs c. 0.1 mm long at apex), apex slightly concave. Flowers 2–2.1 cm long, barely exserted from bracts; calyx 4–5 mm long, tridentate, with unilateral incision 0.7–1 mm, teeth c. 0.5 mm long with blunt apex, semi-translucent white, glabrous (occasionally a few hairs present on teeth); floral tube 1.2–1.5 cm long, narrowly cylindrical at base, slightly widening distally, externally white, glabrous, internally white and glabrous, distally (near throat) pale yellow adaxially, pale purple abaxially, puberulous in apical half; dorsal corolla lobe elliptic, 4.5–5 by c. 2.5 mm, white, glabrous, apex blunt, concave, with a few short hairs; lateral corolla lobes 4–5 by 2–2.5 mm wide at base, elliptic to slightly triangular with obtuse concave apex, white, glabrous; labellum 6–6.5 by 3.5–4 mm, obovate with obscurely bifid apex (incision 0.6–1.5 mm long), white with pale yellow median band of two swollen central lines extending from base of labellum to about 1/2–2/3 towards apex, basally hairy, sides and apex dark purple, with paler lines radiating from centre towards irregularly serrate margin, glabrous; lateral staminodes elliptic, 5–6 by 1.5–2 mm, white or very pale purple, glabrous on both sides; stamen c. 4 mm long; filament 1.9–2 mm long, c. 1.5 mm broad at base, c. 0.9 mm at the point of attachment, pale pink to purple, glabrous; anther spurless, ovate, 2–2.5 mm long (including crest), 1.3–1.5 mm wide at base, connective tissue white sometimes with pink tinge, with glandular hairs on sides and back; anther crest obtuse 0.5–1 by 0.95–1.25 mm wide at base, white or with pink tinge; anther thecae c. 1.5 mm long, dehiscing along entire length, cream-white, pollen white; epigynous glands absent; style white, glabrous; stigma unequally funnel-shaped (dorsal side longer), dorso-ventrally compressed, c. 1 by 0.75 mm, white; ostiole smooth to finely irregularly denticulate margin (no hairs), facing forward; ovary globose to ovoid, 1.5–2.2 by 1–1.5 mm, trilocular, cream white, glabrous, placentation axile. Fruit and seeds not seen.

Distribution — Known only from Kamphaeng Phet and Tak provinces in northern Thailand.

Habitat & Ecology — Lowland deciduous dipterocarp forest, at 100–150 m elevation. Flowering starts in the rainy season and lasts from late May till October. Plants enter dormancy in November to early December. Flowers open in the morning and last a single day.

Conservation status — Information on the Extent of Occurrence , Area of Occupancy and population sizes remains unknown. The populations from Kamphaeng Phet Province are supported by herbarium material, while evidence for this species in Tak is derived from photographs. We therefore propose the category of Data Deficient. The population size was reported by local sellers as large, consisting of thousands of individuals. However , as large numbers of C. micrantha plants have appeared periodically in local markets in the last 4 years, this may become a significant threat to this species over time. Watthana 1509 ( QBG) indicates that at least one population is within the legally protected area of Khlong Lan National Park . More fieldwork to better understand the population sizes as well as introduction of this species into tissue culture to satisfy the demand of the horticultural market, and therefore relieve pressure of harvesting from the field, are needed .

Vernacular names and Uses — Krachiao dong ( กระเจียวดง) = wild curcuma. No uses have been reported, except for the occasional sale of plants as ornamentals. In horticulture, it is known by the name ‘Chocolate curcuma’, a common name referring to the morphotype with rich dark rusty red tinge on the bracts.

Other specimens examined. THAILAND, Kamphaeng Phet Province, Phran Kratai District, Wang Khuang Subdistrict, c. 100–150 m elevation, 13 Aug. 2019, Sutthinut Soonthornkalump Sutt-208 ( SING, including flowers preserved in spirit as part of a single specimen); Kosamphi Nakhon District , Kosamphi Subdistrict, c. 150 m elevation, 14 July 2020, Sutthinut Soonthornkalump Sutt-218 ( BKF, SING, including flowers preserved in spirit as part of a single specimen); Khlong Lan District , Khlong Lan National Park , Namtok Khlong Lan (Khlong Lan Waterfall), 200–400 m elevation, 25 Oct. 2001, S. Watthana 1509 ( QBG); province and exact location unknown, collected from the living collections of Singapore Botanic Gardens, 27 July 2012, J. Leong-Škorničková GRC-111 ( SING,including flowers preserved in spirit) .

Note — Curcuma micrantha has been cultivated at Singapore Botanic Gardens for more than 15 years, following the introduction of plants received in 2003. These were originally purchased by Mr. Tan Jiew Hoe from a nursery in Thailand and their precise location was unknown. This species is one of several commonly subsumed under the name Curcuma parviflora , which has been widely applied to a variety of small, purple-flowered species in Thailand. Leong-Škorničková et al. (2013, reprinted in colour in 2014) showed that the complex was in need of further study and have since described Curcuma prasina from this complex ( Leong-Škorničková et al. 2017).