Curcuma (Ecomatae) maxwellii Skornick . & Suksathan, 2023

Leong-Skornickova, Jana, Soonthornkalump, Sutthinut, Lindstroem, Anders Jan, Niwesrat, Sira, Lim, Sarah Qing & Suksathan, Piyakaset, 2023, Curcuma maxwellii and C. rubroaurantiaca (Zingiberaceae, Zingiberoideae), two new species from Thailand, PhytoKeys 235, pp. 237-248 : 237

Curcuma (Ecomatae) maxwellii Skornick. & Suksathan sp. nov.

Figs 1 , 2 , 3

Diagnosis.

Similar to Curcuma rhomba Mood & K.Larsen in general habit and flower colour, but differs by bracts green to green with slight reddish tinge, puberulent on both sides (versus solid dark red glossy bracts, glabrous on both sides), bracteoles present (vs. bracteoles absent), calyx puberulent throughout (vs. calyx glabrous, except few hairs on teeth), anther with 2-2.5 mm long narrowly conical spurs (vs. ca. 1 mm short broadly conical spurs with blunt apices).

Type.

Thailand, Chiang Rai Province, Chiang Khong District, Rim Khong Subdistrict , 519 m a.s.l., 3 August 2023, Suksathan et al. JLS-4210 (Holotype: QBG! (including flowers in spirit as part of a single preparation); Isotypes: BKF!, E!, P!, SING! (BKF! & SING! including flowers in spirit as part of a single preparation)) Fig. 1 .

Description.

Rhizomatous herb to 0.8 cm tall; rhizome ovoid, ca. 1-1.5 by 0.8-2 cm, with occasional thin branches ca. 4-5 mm diam., brown externally, yellow internally, aromatic with bitter smell; root tubers elliptic, ca. 2.5 by 1.1 cm, light brown externally, pure white internally with translucent white centre. Leafy shoot 95 cm long with 3-6 leaves when flowering; pseudostem 9-30 cm long, composed of leaf sheaths; bladeless sheaths decayed at anthesis; leaf sheaths white-green or with pale pink tinge at base turning green distally, glabrous, but pubescent towards the margins; ligule 4-6 mm long, bilobed, lobes round, hyaline, greenish-white, semi-translucent green, hairy; petiole 4.5-26 cm long (petiole of first leaf shortest, innermost leaves longer), canaliculate, green, glabrous; leaf blade elliptic to elliptic-ovate, 16-44 × 6.5-14 cm, prominently plicate, adaxially bright green, shortly hairy along main veins, abaxially lighter green, glabrous, mid-rib glabrous, green base cordate, apex acuminate, tip ca. 15-20 mm long, pubescent. Inflorescence central (often breaking through the pseudostem), many-flowered; peduncle 5-12 cm long, to 8 mm diam., white or with reddish tinge; thyrse 5-7.5 cm long, 4-6 cm diam. in the middle, without coma; fertile bracts 15-34 per inflorescence, 4-4.5 × 1.8-2.7 cm (larger at the base of the inflorescence), ovate to narrowly ovate, smaller at the apex, light green, sometimes with light reddish tinge throughout the bract, puberulent on both sides (slightly less so on the inside) connate in the lower 1/3; enclosing cincinni with 4 flowers at the base of the inflorescence, the number of flowers per bract gradually decreasing upwards; bracteoles small ca. 1-2 × 0.5-1 mm (outer ones larger, inner ones gradually smaller or totally absent), hyaline, translucent white, glabrous. Flowers 6-7 cm, much exserted from the bracts; calyx to 22 mm long, 3-toothed, unilaterally split 8-10 mm, semi-translucent white with pink tinge, distally cream to greenish, puberulent; floral tube ca. 4.5 cm long, externally pink at the base, gradually redder distally, pubescent, internally light orange, glabrous in basal and distal 1/3, pubescent in middle 1/3, with dorsally placed groove holding the style; dorsal corolla lobe 19-21 × 8-10 mm, triangular ovate, with sides rolled inwards, red outside, light orange inside, glabrous on both sides, apex mucronate, mucro ca. 2 mm; lateral corolla lobes 19-20 × 7-8 mm, narrowly triangular ovate with sides rolled inwards, glabrous, red on outside, light orange on inside; labellum ca. 20 mm long, 5-7 mm broad at basal 5 mm, then broadly ovate, 15-16 mm at widest point, apex bifid with an incision to 7 mm long, labellum orange with darker median bordered by maroon line at basal 4-5 mm; lateral staminodes 16-20 × 8-11 mm, narrowly ovate to bluntly rhomboid, orange with small triangular maroon patch at base (ca. 2 mm), glabrous on both sides. Stamen 16-18 mm long; filament 7-8 mm long, 3.5 mm broad at base, 2 mm broad at apex (the point of attachment to the connective), orange with reddish tinge dorsally, dorsally covered with glandular hairs; anther 13-14 mm long, spurred, connective orange, densely covered with short glandular hairs; anther spurs 2-2.5 mm long, narrowly triangular with sharp tips pointing outwards; anther crest thick, rounded, ca. 1 mm long and ca. 1.5 mm broad at base, orange; anther thecae 8-9 mm, forming narrowly obovate shape, dehiscing along their entire length, pollen white. Epigynous glands 2, ca. 3 mm long, ca. 0.6 mm diam., cream white. Style thin, white, glabrous, placed in a groove in dorsal side of floral tube; stigma ca. 1 mm long, 1 mm wide, white, ostiole ciliate, facing upwards. Ovary 2-3 × 2 mm, trilocular, densely hairy, hairs ca. 1 mm long. Fruits subglobose, ca. 10 mm in diam. (almost ripe), cream white with very slight pink tinge, pubescent; seeds few per capsule (6-10), ca. 4 mm long (almost ripe), light brown, enclosed in semi-translucent white laciniate aril.

Habitat and phenology.

Growing in semi-shade to shaded moist area, near streams, in mixed deciduous forest or primary evergreen hardwood forest, at 400-900 m a.s.l., on granite bedrock. The species flowers from June till September, with fruiting presumably extending into November.

Distribution.

Only known from Chiang Mai and Chiang Rai Provinces, N Thailand.

Eponymy.

We name this species after our late colleague and remarkable botanist James Franklin Maxwell (1945-2015), also known simply as Max, who collected this species in 1992 (Fig. 2 ). With more than 32,000 high quality collections, rich in flowers and/or fruits and carefully prepared with many duplicates and mostly with labels that contain much information, Max ranks amongst the best collectors of Thai plants ( van Welzen 2023).

Vernacular name and uses.

As the vernacular name Wan Pet Ma (ว่านเพชรม้า) is used on several orange-flowered species with red corolla lobes including this species, we propose to use Wan Pet Ma Lanna (ว่านเพชรม้าล้านนา) for this species. Based on the information from the local herbal specialist of the Hmong community, this species, which is locally abundant, has no medicinal uses and only has potential as an ornamental plant.

Provisional IUCN conservation assessment.

During our extensive revision of all Thai Curcuma material in numerous herbaria (as listed in the Introduction), we have found an additional three herbarium collections, which could be confidently assigned to this species. We predict that the main threats to this species might include excessive collection from the habitat for horticultural purposes and trade, as well as conversion of unprotected areas into agricultural lands. However, the species tend to be locally abundant and at least one of the locations (Lam Nam Kok National Park, Khun Korn Waterfall) is in the legally-protected area. We, therefore, propose to treat this species as Least Concern (LC).

Specimens examined.

Paratypes: Thailand, Chiang Mai Province, along the road Fang to Chiang Mai; 27 July 1968; Larsen, K., Santisuk, T. & Warncke, E. 2766; AAU, BKF ; Chiang Rai Province, Mueng District, Koon Gohn Falls [Khun Kon Waterfall], 900 m a.s.l., 20 August 1992, Maxwell, J.F. 92-440 (AAU, KUN, CMU); Khun Korn Fall [Khun Kon Waterfall], 680 m a.s.l., 22 June 2002, Chamchumroon, V., Suphuntee, N., Koonkhunthod, N., Ngernsaengsaruay, C. & Tetsana, N. 1601 (BKF, 2 sheets); Doi Tung, 26 Sep 1967, Iwatsuki, K., Fukoka, N., Hutoh, M. & Chaiglom, D. 13271 (BKF) .

Notes.

As already pointed out by Lưu et al. (2017), all the material seen labelled as C. rhomba from Thailand in Mood and Larsen (2001) is distinct from the material from southern Vietnam and, in fact, represents several species. The specimen Larsen & al. 2766 represents C. maxwellii and is cited here amongst the paratypes. For this reason, we have compared Curcuma maxwellii to C. rhomba in the diagnosis. In northern Thailand, C. maxwellii might be confused with Curcuma bicolor , which also has red-orange flowers and is also known to occur in Chiang Mai and Mae Hong Son Provinces. The two species are easy to recognise when flowering as the flowers of Curcuma bicolor are much more open and the basal half of the staminodes is dark red (Fig. 3 ).

Outside of Thailand, Curcuma maxwellii is also similar to Curcuma flammea Škorničk. described from Laos, by general habit and shape of the inflorescence, but differs by adaxially glabrous leaf blades (vs. shortly puberulent), bracts light green with more or less reddish tinge (vs. bracts white, pink to dark red), labellum without prominent basal claw, orange throughout with two thin red lines bordering median band at base (vs. prominently violin-shaped labellum with a prominent broad claw, bright orange with rich red shading and ornamentation), staminodes orange with a small maroon triangular spot at base (vs. staminode mostly bright red with distal part orange), anther with 2-2.5 mm long spurs, not producing mucilage (vs. 3-4 mm long, producing a mucilage in C. flammea ).

Curcuma maxwellii is distinct from C. stenochila by the shape of the labellum, which has a narrow basal claw in C. stenochila , similar to that of C. lindstromii .

Figures

Figure 1. Curcuma maxwellii Skornick. & Suksathan at the type locality A habit B inflorescence (top view) with detail of flower in front view C detail of leaf sheaths and ligules D rhizome E inflorescence with detail of flower in side view F two fertile bracts, three flower buds from the same cincinnus as the dissected flower, dissected flower (from left: floral tube with ovary, calyx and stamen attached, upper row dorsal and lateral corolla lobes, lower row lateral staminodes and labellum G stamen still attached to floral tube from front, back and side view. All from the type collection, Suksathan et al. JLS- 4210. Photographed by Jana Leong-Skornickova.

Figure 2. James Franklin Maxwell in CMU Herbarium in 2013. Photographed by J. Leong-Skornickova.

Figure 3. Comparison of flower in front view of A Curcuma bicolor and B C. maxwellii. Photographed by Jana Leong-Skornickova.