Apiaceae, one of the largest families of angiosperms, comprises 3,820 species in 466 genera (Plunkett et al., Reference Plunkett, Pimenov, Reduron, Kljuykov, Wyk and Ostroumova2018) mostly distributed in northern temperate regions and high-altitude areas in the tropics (Sayed-Ahmad et al., Reference Sayed-Ahmad, Talou, Saad, Hijazi and Merah2017). The genus Ferula is one of the largest genera in Apiaceae, distributed from Central Asia (mainly in Iran and Afghanistan) westward to the Mediterranean region (Pimenov & Leonov, Reference Pimenov and Leonov1993; Sahebkar & Iranshahi, Reference Sahebkar and Iranshahi2011; Estekhdami & Dehsorkhi, Reference Estekhdami and Dehsorkhi2019; Mohammadhosseini et al., Reference Mohammadhosseini, Venditti, Sarker, Nahar and Akbarzadeh2019). It includes c. 170 species, most of which are important medicinal plant resources in montane regions, with a few in arid climates (Yaqoob & Nawchoo, Reference Yaqoob and Nawchoo2016). Some Ferula species are known for their medicinal value in the treatment of stomach disorders, wheezing, lymphatic tuberculosis, intestinal ulcers and tonsillitis, and for detoxification, detumescence and analgesia (Shan et al., Reference Shan, She, Shan and She1992).

Ferula sinkiangensis K.M. Shen was reported as a new species in 1975 based on its holotype (herbarium XJBI, A093) and some paratypes (A069, A072 and A119), all of which were collected in Baishidun, Yining County, Xinjiang, China (Shen et al., Reference Shen, Ramil, Yang and Xu1975). Endemic to Xinjiang, it is a herbaceous perennial and monocarpic plant that grows in semiarid steppe ecosystems (She & Watson, Reference She, Watson, Wu, Raven and Hong2005). The species is believed to grow vegetatively for c. 7 years before flowering and fruiting (Shen, Reference Shen1987), and takes 15 years to complete its life cycle (D.-Y. Tan, unpubl. data, 1995–2009). It is recorded in the Chinese Pharmacopoeia (Chinese Pharmacopoeia Commission, 1978) and is used as a medicinal herb in China for the treatment of stomach disorders, wound infections, joint pain, and symptoms of ovarian cysts, and for detumescence (Shen, Reference Shen and Shen2011). Since 1970, F. sinkiangensis has been threatened by habitat loss, environmental changes and overexploitation (Zhao et al., Reference Zhao, Tan, Xiang and Cheng2009). In China, F. sinkiangensis is categorized as a Critically Endangered species (Wang & Xie, Reference Wang and Xie2004; Qin et al., Reference Qin, Yang, Dong, He, Jia and Zhao2017) and a national second-class protection plant (Fu, Reference Fu1992; National Forestry and Grassland Administration, Reference National Forestry and Grassland Administration2021), but it has not yet been assessed on the IUCN Red List. Because of its narrow distribution range, medicinal value and threatened status, a c. 67 ha fenced reserve was established in 2004 in Yining County to protect the species.

The study site is located on the north-west border of Xinjiang in the centre of the Yili River Valley Basin. This area is characterized by desert conditions and gravelly clay slopes (Fig. 1).

Fig. 1 Location of the remaining population of Ferula sinkiangensis in Yining County, and the survey sites in Nileke County and Manashi County, Xinjiang, China.

We first examined the specimens of F. sinkiangensis in the Chinese Virtual Herbarium and found that the species has also been collected from Nileke and Manashi counties in Xinjiang. Based on the collection sites and habitat records of these specimens we surveyed the distribution range during 2016–2022 in three counties in Xinjiang: Yining, Nileke and Manashi. After 7 years of investigation we found two populations of F. sinkiangensis, in Yining and Nileke, but not in Manashi. The Nileke population had only four individuals, but these disappeared in 2018 (Li et al., Reference Li, Su, Yang, Cao and Feng2020) as a result of unknown causes (it is possible they were harvested by local people). There is therefore only one remaining population of F. sinkiangensis, with one subpopulation in each of two valleys in Yining, at altitudes of 1,065–1,139 m, separated by a small hill. We investigated population age structure during April–May in 2022 and 2023. We established 18 survey plots (each measuring 20 × 20 m) in each of the two subpopulations and placed four 3 × 3 m quadrats in each plot, resulting in a total of 144 sample quadrats. We counted the number of surviving individuals and the number of basal leaves of each individual in each quadrat. Considering the small population size and degree of threat, we used space instead of time to identify age groups according to the number of basal leaves, which increases with age (Harper & White, Reference Harper and White1974), identifying nine age classes. We calculated the area of occupancy and extent of occurrence using the IUCN Guidelines (IUCN, Reference IUCN2022).

In 2022 and 2023, we found a total of 673 and 1,360 individuals, respectively, in the surveyed plots of subpopulation I and 568 and 947 in the surveyed plots of subpopulation II. We found no flowering individuals in 2022 and only five flowering individuals in 2023 (Table 1). The number of basal leaves per individual had an inverted J-shaped distribution in both subpopulations. The highest number of individuals was in the 3–4 year age group, after which the number of individuals declined with increasing age (Fig. 2), indicative of a relatively stable age structure.

Table 1 Number of Ferula sinkiangensis individuals recorded in our surveys of two subpopulations in Yining County, Xinjiang, China (Fig. 1), in 2022 and 2023.

Fig. 2 Frequency distribution of the number of basal leaves in the two Ferula sinkiangensis subpopulations in Yining County, Xinjiang, China (Fig. 1).

Although F. sinkiangensis was previously widely distributed in the premountain desert areas of the western Junggar Basin, these areas have been converted into farmland, resulting in the destruction and loss of the species’ habitat (Li et al., Reference Li, Fu, He, Fan and Li2016). Additionally, extensive grazing around the F. sinkiangensis reserve constrains its growth, as any plants that grow outside the reserve are consumed by cattle and sheep, preventing the population from expanding (Plate 1). Furthermore, despite legal prohibitions against harvesting F. sinkiangensis, this still occurs, threatening the species’ survival. Because of its narrow distribution range and decreasing number of individuals, F. sinkiangensis is categorized as Critically Endangered on the Threatened Species List of China's Higher Plants based on criterion A2c (Qin et al., Reference Qin, Yang, Dong, He, Jia and Zhao2017). We propose that the species should be categorized as Critically Endangered on the IUCN Red List based on criterion B2ab(iii), C2a(i) and D (IUCN, Reference IUCN2022); i.e. we calculate the area of occupancy to be the same as the extent of occurrence at 4 km² (B2), there is a single location (a), which is affected by cattle and sheep grazing, and human disturbance, resulting in a continuing decline in extent and quality of habitat (b(iii)), and the results of the surveys conducted in both years show that there are fewer than 50 mature individuals within each subpopulation (C2a(i)) and the whole population (D). The area occupied by the two subpopulations falls within a single cell of a 2 × 2 km grid, and therefore both the extent of occurrence and area of occupancy are < 4 km².

Plate 1 (a) The remaining population and habitat of Ferula sinkiangensis in Yining County, Xinjiang, China, (b) the effects of grazing, (c) the fruiting stage and (d) the flowering state. Photos: Wenjun Li; (a), (b) and (d) photographed in 2023, (c) in 2018.

Rare and threatened species often face increased risk of genetic drift and inbreeding because of their small population sizes and limited geographical ranges (Nei et al., Reference Nei, Maruyama and Chakraborty1975; Hamrick et al., Reference Hamrick, Godt and Sherman-Broyles1992; Hamrick & Godt, Reference Hamrick and Godt1996; Frankham, Reference Frankham1997; Nybom, Reference Nybom2004). It is crucial to prioritize measures aimed at preventing population degradation for such species, including in situ and ex situ conservation strategies (Li et al., Reference Li, Zhang and Zhang2014; Wang et al., Reference Wang, Ma, Chen, Li, Dao and Sun2016; Han et al., Reference Han, Tao and Sun2020). The stable age structure of the F. sinkiangensis population in Yining County can be attributed to the construction of the fence around the reserve in 2004 and the implementation of grazing bans inside the reserve. However, the population faces challenges to its regeneration, with only a few seeds produced by mature plants (of which there are < 50). To protect this species effectively, we recommend the following in situ and ex situ conservation actions: (1) further studies on the species’ phenology, pollination, seed dispersal, population dynamics and genetic variation; (2) development of an ex situ conservation plan, including artificial cultivation, tissue culture and core germplasm preservation; and (3) strengthening of reserve management practices and increasing awareness among local residents regarding the importance of conserving this species (Li et al., Reference Li, Zhang and Zhang2014; Wang et al., Reference Wang, Ma, Chen, Li, Dao and Sun2016; Han et al., Reference Han, Tao and Sun2020; Zhang et al., Reference Zhang, Zhou, Liu, Mo, Zhang, Wang and Shen2020; Paglia et al., Reference Paglia, Luber, Mansano and Freitas2022).