﻿Panaxsiamensis J. Wen, a new species of the ginseng genus (Panax, Araliaceae) from northern Thailand

﻿Abstract We herein describe a new species, Panaxsiamensis J. Wen, from the tropical monsoon forests in northern Thailand. Panaxsiamensis is characterized by a combination of characters including horizontally elongated rhizomes with thick internodes, 3–5 whorled leaves each with 7–9 sessile and lanceolate leaflets, lanceolate bracteoles not persisting at the fruiting stage, 2-locular ovaries, and red fruits with a black top. The new species is most closely related to Panaxzingiberensis C.Y. Wu & Feng from southeastern Yunnan province of China, sharing the character of sessile leaflets, but differing in that P.siamensis has well developed, elongated rhizomes (vs. compact, ginger-like rhizomes and rootstock in P.zingiberensis), and 7–9 leaflets (vs. (3–) 5–7 leaflets in P.zingiberensis). We also compare Panaxsiamensis to other related Asian Panax species, including P.assamicus Banerjee, P.bipinnatifidus Seem., P.pseudoginseng Wallich, and P.vietnamensis Ha & Grushv. The new taxon is preliminarily assessed as Vulnerable (VU D2), according to the IUCN Red List criteria. A taxonomic key is provided to facilitate the identification of P.siamensis and its close allies.

In spite of its economic (Hu 1976;Proctor 1996) and biogeographic (Wen 1999;Zuo et al. 2017) importance, the species delimitation of Asian Panax has been controversial, largely involving the circumscription of Panax japonicus C.A. Meyer and Panax pseudoginseng Wallich (Li 1942;Hara 1966Hara , 1971;;Zhou et al. 1975;Hoo and Tseng 1978;Yang 1981;Xiang and Lowry 2007).Molecular phylogenetic analyses have strongly suggested that Panax japonicus is endemic to Japan and forms a clade with two of the medicinally important species: Panax ginseng and P. quinquefolius (Wen and Zimmer 1996;Lee and Wen 2004;Zuo et al. 2011Zuo et al. , 2017)).A number of studies have supported the distinctiveness of Panax pseudoginseng as a species that is narrowly distributed in Nepal and adjacent areas of Xizang, China, and as closely related to Panax stipuleanatus Tsai & Feng, which is from southwestern China and northern Vietnam (Lee and Wen 2004;Zuo et al. 2011Zuo et al. , 2017)).Zhou et al. (1975) also described Panax zingiberensis from southeast and southern Yunnan that has ginger-like roots persistent in older plants, and leaflets without petiolules.
During our revisionary studies of Panax, we discovered a new species from northern Thailand.This species had been recognized as Aralia pseudoginseng (Wallich) Benth.ex C. B. Clarke var.angustifolia (Burkill) Craib (Craib 1931).Hara (1971) and more recently Esser and Jebb (2019) treated it in the genus Panax [as P. pseudoginseng Wallich var.angustifolius (Burkill) H. L. Li], which has been treated as Panax bipinnatifidus Seem.(Zuo et al. 2015(Zuo et al. , 2017)).The new species is highly distinct from Panax bipinnatifidus and several related species from Asia (see Discussion below).
Additional specimens examined.Thailand.Chiang Mai: Mae Soi Ridge, Mae Soi Subdistrict, near Ban Bah Cluary (Meo Village), 1475 m, 11 Aug 1991, in fl, shaded place, mixed evergreen hardwood and pine forest, J. F. Maxwell 91-722 (A, CMUB, E); Ob Luang National Park, Mae Soi Conservation Area, Bah Gluay (Hmong) village area, between the Ranger Station and the village, on the N side of the road passing through the Bah Gluay village, elev.1550 m, evergreen forest, plant c. 60-70 m tall, fruits red with a black top, 04 Nov 2003, fr, J. Wen 7371 (KUN, US).
Phenology.Flowering in August; fruiting in November to December.Distribution.Northern Thailand; elevation 1350-1550 m.
Ecology.In shaded areas of monsoon evergreen hardwood forests, or in mixed evergreen hardwood and pine forests, granite bedrock.
Etymology.The species epithet denotes the geographic distribution of the species in Thailand.

Conservation
The area of occupancy (AOO) of this species as measured with a 2×2 grid is estimated to be 12 km 2 ; the extent of occurrence (EOO) is estimated to be 39.54 km 2 .Apart from habitat destruction, no specific threats are known.It is not found in cultivation, and it is not known from any ex situ collections.With a restricted area of occupancy, only three known locations, and a plausible future threat due to stochastic events or habitat disturbance brought about by human activities near villages, Panax siamensis is preliminarily assessed with a status of Vulnerable (VU D2) according to IUCN Red List Criteria (IUCN 2012, 2022).

Discussion
The new species Panax siamensis is distinguished from other Panax species by a combination of characters including horizontally elongated rhizomes with thick internodes, 3-5 whorled leaves each with 7-9 sessile and lanceolate leaflets, lanceolate bracteoles not persisting at the fruiting stage, 2-locular ovaries, and red fruits with a black top.The new taxon is sister to Panax zingiberensis from southeastern Yunnan province of China (J.Wen, unpublished), sharing the character of sessile leaflets.The two species differ in that P. siamensis has elongated rhizomes (vs.compact ginger-like rhizomes in P. zingiberensis), and 7-9 leaflets (vs.5-7 leaflets in P. zingiberensis).As P. zingiberensis is medicinally important (Zhou et al. 1975), it is important to explore the chemistry of P. siamensis to test its medicinal value.
Even though Panax siamensis was recently treated as part of P. pseudoginseng (Esser and Jebb 2019), the new species is highly distinct from Panax pseudoginseng, which is narrowly distributed in Nepal and neighboring Xizang of China (Wallich 1829;Wen 2001).Panax pseudoginseng has fusiform tubers that are single or fascicled (vs.tubers absent in P. siamensis), rhizomes short and upright (vs.elongate and horizontal in P. siamensis), leaves with stipules (stipules absent in P. siamensis), and fruits that are red throughout (vs.fruits red with a black top in P. siamensis) (Wen 2001;Yoo et al. 2001).
Panax siamensis can be easily distinguished from P. bipinnatifidus in that the latter has horizontal rhizomes with slender internodes and subglobose nodes (vs.horizontal rhizomes with thick and short internodes, i.e., bamboo-like, in P. siamensis), leaves with 5 (-7) leaflets (vs.7-9 leaflets in P. siamensis), and terminal umbels with fewer flowers (25-50 flowers in P. bipinnatifidus, vs. 70-90 flowers in P. siamensis).Ecologically, Panax bipinnatifidus occurs in deciduous or mixed deciduous and coniferous forests in western China to the Himalayas at higher elevations of 2000-3600 m (Wen 2001), while P. siamensis occurs in monsoon evergreen hardwood forests, or in mixed evergreen hardwood and pine forests around 1350-1550 m.
We herein provide a key to Panax siamensis and its close allies to help differentiate the species.

Figure 1 .
Figure 1.Illustration of Panax siamensis J. Wen based on J. Wen 7371 (US) A habit B horizontal rhizome with base of stem C leaflet margin D leaflet abaxial surface E infructescence F enlarged infructescence G bracteoles subtending pedicels at flowering stage H older flowers after petals falling off, showing 2-locular ovary I young fruiting stage J seed K seed surface.

Figure 2 .
Figure 2. Field images of Panax siamensis and its habitat A habitat in monsoon evergreen forest B infructescence showing red fruits with a black top C habit.Photo credit: A (Ricky Ward), B, C (Jun Wen).