﻿Curcumamaxwellii and C.rubroaurantiaca (Zingiberaceae, Zingiberoideae), two new species from Thailand

﻿Abstract Curcumamaxwelliisp. nov. and Curcumarubroaurantiacasp. nov. (Zingiberaceae, Zingiberoideae, Zingibereae), two new red-orange-flowered species from Thailand, are described. They are compared to the morphologically closest species from the Curcumasubgen.Ecomatae and detailed descriptions, colour plates and information on their distribution, ecology, phenology and uses are provided. Preliminary IUCN conservation assessments for both of these species are proposed as Least Concern


Introduction
Curcuma L. (Zingiberaceae, Zingibereae) is one of the largest ginger genera widely distributed in South and Southeast Asia and South China, with a few species extending to northern Australia and the South Pacific (Záveská et al. 2012).The number of Curcuma species have been steadily rising in past 30 years from about 80 to the current estimate of more than 150 species (Leong-Škorničková et al. 2022).The genus is economically important with turmeric (Curcuma longa L.) being perhaps the best-known example, but very many other species are used as spices, condiments, vegetables, medicinal plants and several species are a prominent part of the tropical horticultural industry.The introduction about the genus and its subgenera was given in our recent works (Leong-Škorničková et al. 2015(Leong-Škorničková et al. , 2020(Leong-Škorničková et al. , 2021) ) and is, therefore, not repeated here.
While working on the Curcuma account for the Flora of Thailand, we have realised that the herbarium material misidentified as C. rhomba Mood & K.Larsen or Curcuma stenochila Gagnep. in Thailand is heterogeneous.Although most material had similar shape of leaf blades and inflorescences and the flowers were mostly described as orange with red corolla lobes, the geographically distinct clusters, differences in plant indumentum and evidence from an existing photographic material confirmed the need to re-collect living flowering material from different parts of Thailand to make further conclusions on the taxonomic treatment of the taxa involved.Our work on this complex of species with bright orange flowers with red corolla lobes already led to description of Curcuma lindstromii from Chanthaburi and designating the lectotype of C. stenochila (Leong-Škorničková et al. 2022).Additional targeted fieldwork was done in 2023 in the following Provinces: Chiang Rai, Sakon Nakhon, Loei, Chayaphum and Phetchabun.The newly-re-collected material confirmed our suspicion that additional two taxa should be recognised and these are, therefore, described below as Curcuma maxwellii and C. rubroaurantiaca.
Although it remains unclear if Curcuma stenochila occurs in Thailand at all, it is clear that both of the two species described here are sufficiently distinct from it as elaborated in notes under each of the two species.

Material and methods
The description of these new species is based on measurements from living flowering material and examination of herbarium specimens including flowers preserved in spirit.All extant herbarium material of Curcuma was examined at AAU, BK, BKF, BM, CMU, E, K, L, P, PSU, QBG and SING.The style of description follows the recent works of Leong-Škorničková et al. (2013Leong-Škorničková et al. ( , 2014Leong-Škorničková et al. ( , 2017Leong-Škorničková et al. ( , 2020Leong-Škorničková et al. ( , 2021Leong-Škorničková et al. ( , 2022)).The general plant terminology follows Beentje (2016).The preliminary conservation assessments are based on the guidelines of the IUCN (2022).
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 (1945Maxwell ( -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 (ว่ านเพชรม้ า) is used on several orange-flowered species with red corolla lobes including this species, we propose to use Wan Pet Ma Lanna (ว่ านเพชรม้ าล้ านนา) 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 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).
Habitat and phenology.Growing in semi-shade and edges of evergreen forest mixed with bamboo, in moist places, at 200-800 m a.s.l., on sandstone as well as limestone bedrocks.The species flowers from July till September, with fruiting presumably extending into November.
Etymology.The specific epithet refers to its bright red and orange flowers.Vernacular name and uses.Similarly to the previous species, the vernacular name Wan Pet Ma (ว่ านเพชรม้ า) is used also on this species; we, therefore, propose refining the vernacular name to Wan Pet Ma Isan (ว่ านเพชรม้ าอี สาน) for this species.No uses were reported, but the species has a good potential as an ornamental plant.
Provisional IUCN conservation assessment.In addition to our collection, we have found an additional two herbarium collections from Loei Province (Phu Luang), two collections from Chayaphum Province (Chulabhorn Dam and Phu Kiew) and two specimens from Petchabun, which could be confidently assigned to this species.Most of these areas are in National Parks under legal protection.The species was also sighted by us in an additional two legally-protected areas, namely Phu Pha Lom Forest Park (Loei Province) and Phu Phan National Park (Sakon Nakhon Province).We, therefore, propose to treat this species as Least Concern (LC).

Figure 1 .
Figure 1.Curcuma maxwellii Škorničk.& 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-Škorničková.

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

Figure 4 .
Figure 4. Curcuma rubroaurantiaca Škorničk.& Soonthornk.at the type locality A habit B inflorescence 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 flowers and dissected flower (from left: ovary with epigynous glands, calyx, floral tube (dissected longitudinally), upper row dorsal and lateral corolla lobes and stamen, lower row lateral staminodes and labellum G stamen from front, back and side view.All from the type collection, Soonthornkalump Sutt-242.Photographed by Sutthinut Soonthornkalump.