Curcuma stahlianthoides Škorničk. & Soonthornk., 2022

Curcuma stahlianthoides Škorničk. & Soonthornk. View in CoL , sp. nov. (subg. Hitcheniopsis) — Fig. 1 View Fig , 2 View Fig

Similar to Curcuma leonidii Škorničk. & Luu in overall habit, having an inflorescence composed of multiple green bracts,and overall shape of the flowers, but differs in having branched rhizomes with short and stout branches,cream in cross section (vs rhizomes not branched,globose,c.1 by 1 cm,light orange in cross section), leaf blades narrowly elliptic up to 25 by 2.9 cm, plication obscure (vs elliptic, up to 22 by 6.5 cm, prominently plicate) and labellum white with yellow median band (vs labellum with median band red at base, yellow distally). — Type: Sutthinut Soonthornkalump Sutt-228 (holo BKF!, consisting of a sheet and spirit collection; isotype BK!, E!, P!, QBG!, SING! including flowers in spirit as part of a single specimen), Thailand, Nakhon Phanom Province, Na Wa District, Na Wa Subdistrict , alt. 150 m, 21 May 2022, flowering .

Etymology. The specific epithet ‘ stahlianthoides ’ refers to the flowers, which are so typical for the alliance of species previously treated in the separate genus Stahlianthus .

Rhizomatous perennial herb up to 50 cm tall. Rhizome irregularly ovoid to pear-shaped, c. 2–3 by 0.8–1.4 cm, often with lateral branches up to 1 cm long, 0.5 cm diam, light brown to brown externally, covered with rusty-coloured and decayed scales, cream internally, weakly aromatic, bitter with menthol-like taste. Root tubers ovate to fusiform, 1.5–2 by 0.7–1.2 cm, light brown externally, cream internally. Leafy shoot with 2–4(–5) leaves when flowering; pseudostem 6 –15 cm long, composed of leaf sheaths, more obvious when young as the leaf sheaths disengage with age; leafless sheaths 3–4, plain green, glabrous, soon decaying, with shortly mucronate apex (c. 1 mm long), margin hyaline, puberulent; leaf sheaths plain green, glabrous, margin hyaline; ligule 0.5–1 mm long, obscurely bilobed, semitranslucent white, glabrous, membranaceous, turning papery with age, margin with sparsely stipitate hairs of c. 0.1 mm long at upper margin; petiole up to 20 cm long, canaliculate, plain green, adaxially glabrous, abaxially puberulent; lamina narrowly elliptic, 8–25 by 0.8–2.9 cm, adaxially green, puberulent, abaxially somewhat paler, densely puberulous, midrib green, adaxially glabrous, abaxially puberulous, base slightly oblique, cuneate to acute, apex acuminate, margin hyaline, semitranslucent white, c. 0.5 mm wide, glabrous. Inflorescence lateral, usually appearing before the leafy shoots, often partly embedded in the soil (especially in plants growing in full sun); peduncle basally obscured by leafless sheaths and exceeding it by 4–12 cm long, c. 3–5 mm diam, light greenish cream, glabrous; thyrse 2 –5 cm long, 1–6 cm diam in the middle, coma bracts absent; fertile bracts 2 –11 per inflorescence, broadly ovate to ovate, 2–4 by 1.5–2.4 cm (uppermost bracts are usually smaller), apex strongly reflexed, slightly mucronate (mucro c. 0.1 mm long), plain green, puberulous on both sides, connate in the lower 1/3 to 1/2; cincinni with up to 6 flowers at the base of the inflorescence but only 1 or 2 flowers at the top with other flowers in uppermost bracts often underdeveloped or aborted and covered by developed bracteoles; bracteoles one per flower, narrowly triangular, boat-shaped with acute apex, up to 8.5 mm long, 2–2.2 mm wide at base (outer ones larger, inner ones gradually smaller), hyaline, semitranslucent white, glabrous. Flowers 4.7–5.3 cm long, strongly exserted from the bracts; calyx 9.3–9.5 mm long, 3-toothed, with unilateral incision c. 3.5 mm deep, semitranslucent white, glabrous excepted for a few stipitate hairs at margin of c. 0.1 mm long; floral tube 2.7–3.2 cm long, narrowly cylindrical at base for 2–2.3 cm above the ovary, narrowly funnel-shaped distally, externally white at base, distally cream to pale yellow, glabrous, internally of the same colours, glabrous in basal half, gradually puberulent with short glandular hair distally, with denser and more prominent yellow hairs near the throat (the yellowcoloured part), groove holding the style positioned dorsally; dorsal corolla lobe obovate, 12.5–13 mm long, 2–2.2 mm at base ( 4.3–4.5 mm at widest point), apex hooded, minutely mucronate (mucro c. 0.4 mm long), white with semitranslucent veins, glabrous, margin hyaline, glabrous; lateral corolla lobes elliptic to triangular-oblong, 12.5–12.8 by 4.3–4.8 mm, apex obtuse, white with semitranslucent veins, glabrous, margin hyaline, glabrous; labellum broadly obovate to broadly spathulate, 23.4–25.6 by 21.5–23 mm, apex bilobed with an incision c. 7 mm long, pointing more or less horizontally to slightly downward, white with bright warm yellow swollen median extending from the base to about 3/4 towards the apical margin (ending approximately at the incision separating the two lobes), adaxially with sparse short glandular hairs throughout, much denser and with longer hairs on entire median, especially toward the base; lateral staminodes irregularly narrowly obovate to obscurely spathulate with obtuse apex curving towards the labellum, 19.5–20.6 by 1.1–1.2 mm at base ( 6.9–8.1 mm at widest point), very pale yellow at base, white distally, glabrous on both sides with sparse glandular hairs basally; stamen c. 9 mm long; filament 2.4–2.5 mm long, 1.5–1.8 mm broad at base, less than c. 0.6 mm broad at the point of attachment, very pale yellow with semitranslucent veins, with sparse glandular hairs abaxially, denser adaxially; anther 6.7–7.1 mm long, connective white, glabrous with glandular hairs on the sides, anther spurs absent, anther crest obovate to obscurely bluntly rhomboid, 3.2–3.7 by 2.6–3.2 mm, white, rather thick, glabrous; anther thecae 2.7–3 mm long, dehiscing along their entire length, pollen white; epigynous glands absent; style white, glabrous; stigma funnel-shaped, dorsoventrally flattened, c. 1.5 by 1.3 mm, white; ostiole with irregularly serrulate margin, facing forwards; ovary ovoid, 3–3.7 by 1.3–1.4 mm, trilocular, pale yellowish cream, glabrous. Fruits obovoid to subglobular capsules, 10–12 by 6–7 mm (almost ripe), greenish white, glabrous, dehiscing irregularly, with 18–30 seeds; seeds irregularly obovoid to ovoid, 2.9–3.2 by 1.7–2.3 mm, brown (almost ripe) shiny, with basally attached semitranslucent white, laciniate aril.

Distribution — Known only from Nakhon Phanom Province in northeastern Thailand.

Habitat & Ecology — The species grows in edges of the scrub forest mixed with bamboos, usually in occasionally flooded areas, at ± 150 m elevation. Flowering between April to May; fruiting around late of May to June.

Conservation status — The species is only known from a single location. While the type population consists of over a thousand mature individuals with likely more populations in similar habitats in this or adjacent provinces, the Extent of Occurrence and Area of Occupancy remain at this point unknown. Although the species does not have a good horticul- tural potential for cut-flower industry or landscaping, it is still occasionally sold as an ornamental at local markets, and may likely be targeted by local plant collectors and ginger enthusiast growers. Also , the area with the existing population is not under any legal protection and is in close proximity to land used for agriculture. We therefore propose the category of Vulnerable ( VU D2 ) .

Vernacular name & Uses ––Thai common name Bussarin ( บุศรินทร์) = Lotus of Indra (a deity in Hinduism, Buddhism and Jainism). No uses were reported, but the species is occasionally sold in local markets as an ornamental and the flowers are used for offerings.

Notes — As outlined in the introduction and the diagnosis, we consider C. leonidii as morphologically the most similar species due to the inflorescence composed of up to 11 fertile bracts, which is rare in species with pure white and yellow gullet-shaped flowers. Because the rhizome of C. stahlianthoides is branched, it usually produces multiple shoots that can develop an inflorescence from each shoot, unlike C. leonidii which has unbranched rhizomes with one leafy shoot per rhizome. In addition, these two species are about 900 km apart with C. stahlianthoides occurring only in Nakhon Phanom province in northeastern Thailand, while C. leonidii occurs in the south of Vietnam. The inflorescence structure distinguishes C. stahlianthoides from all other species from the former genus Stahlianthus . The mature plants are easy to recognize in both herbarium and living material by the slender habit with narrow leaves. While other species in subg. Hitcheniopsis having such narrow leaves exist, e.g., C. rufostriata Škorničk. & Soonthornk. ( Soonthornkalump et al. 2021) or C. prasina Škorničk. ( Leong-Škorničková et al. 2017) , these have central inflorescences on long slender peduncles (easily seen in herbarium specimens) and predomi- nantly purple flowers. In addition, C. rufostriata has pink fertile bracts with rusty-red-brown striation.

As observed in the field, the ripe capsules of C. stahlianthoides dehisce irregularly, releasing prominently arillate seeds, which were carried away by ants (see Fig. 1f View Fig ).Ant-aided seed dispersal, myrmecochory, is a short-distance mechanism of dispersal. It has been shown to be an important drive for plant diversification and has evolved in at least 77 families and over 11 000 species ( Lengyel et al. 2009, 2010). In general, there are not many works on seed-dispersal in Zingiberaceae , but myrmecochory has been previously documented for several Globba L. species ( Pfeiffer et al. 2004, Zhou et al. 2007), Renealmia Houtt. ( Mabberley 2008) , Roscoea Roxb. ( Nordhagen 1932, Cowley 2007) and also suggested for Curcuma ( Leong-Škorničková & Newman 2015) . Pfeiffer et al. (2004) reported that seed arils of Globba francisci Ridl. and G. propinqua Ridl. in Borneo function as an elaiosome (i.e., lipid-rich seed appendages that attract ants and serve as rewards in exchange for dispersal), and at- tracted 23 different ant species, with some carrying seeds for over 8 m from the source. Subsequently, Zhou et al. (2007), studied G. lancangensis Y.Y.Qian in China, and concluded that 12 species of ants visited and moved seeds up to 3.35 m from the original plant. The ant-aided dispersal of C. stahlianthoides fits well with our observation of the type population, where a large number of plants are more or less evenly spread over the area, even though the morphology of the rhizomes does not support this distribution pattern. Myrmecochory, as a secondary seed-dispersal mode was also reported in the Neotropical Renealmia alpinia (Rottb.) Maas ( García-Robledo & Kuprewicz 2009) , and ants were also observed to disperse seeds of Globba leucantha Miq. in Bukit Timah Nature Reserve ( Singapore), as well as various seed-setting Curcuma species (e.g., C. petiolata Roxb. ) in cultivation at the Singapore Botanic Gardens by the last author. Given that seed morphology across the Globba and Curcuma is highly similar, and occurs in number of other Zingiberaceae genera, it is very likely that myrmecochory is a common, but grossly under-reported seed dispersal mode in gingers, and certainly deserves future studies. Better understanding of mutualistic relationships with other species will shed more light on provisioning ecological services gingers and other plants offer within their ecosystem.