Sedum ichangensis, a new species of Crassulaceae from Hubei, China

Abstract Sedum ichangensissp. nov., from Yichang, Hubei province, central China, is described and illustrated. The new species is similar to S. elatinoides and S. rosthornianum in its leaf and carpel morphology and differs in its creeping stems and solitary flowers. The conservation status of S. ichangensis was assessed as Endangered according to the IUCN Red List criteria.


Introduction
Sedum Linnaeus (1753: 430), the largest genus in the family Crassulaceae with about 430 species, is particularly diverse in East Asia, the Mediterranean and North America (Linnaeus 1753;'t Hart and Bleij 2003;Thiede and Eggli 2007). Sedum can easily be distinguished by its usually alternate leaves, sessile carpels with slightly connate at the base, separate, mostly yellow or white petals and stamens with two whorls (Thiede and Eggli 2007); however, molecular studies have revealed that Sedum is a highly polyphyletic group (Nikulin et al. 2016) which may be due to the high morphological plasticity and variability within the genus (Carrillo-Reyes et al. 2009). In China, 121 species were recorded in the "Flora of China" (Fu and Ohba 2001 Jin & B. Y. Ding (2013: 34) and S. peltatum M. L. Chen & X. H. Cao (2017: 847).
According to the recent taxonomic treatment of Fu and Ohba (2001), the species of Sedum in China are divided into three sections, viz. Sedum sect. Sedum, sect. Oreades (Fröderström) K.T. Fu and sect. Filipes (Fröderström) K.T. Fu. The section Sedum is distinct from both sections Oreades and Filipes in its adaxially gibbous carpels and follicles (vs. carpels and follicles not gibbous); while the sect. Oreades differs from the sect. Filipes in its spurred (vs. spurless) leaf base and petals that are mainly yellow (vs. mainly white or reddish-purple) (Fu and Ohba 2001).
An unknown Sedum species, belonging to the sect. Filipes, was discovered in Hubei Province, Central China. The species is described as new to science in this study.

Material and methods
Three scattered populations of an unknown Sedum species were discovered in Yichang city of Hubei Province, Central China in 2014. These populations were continuously observed over 2 years. Fresh specimens collected from these populations were morphologically studied and illustrated. The distribution map was constructed with Arcgis 10.2, using data provided on the specimen labels.
Phenology. Flowering from early May to July, fruiting from August to October. Distribution and habitat. Sedum ichangensis is known from Longzhouping town of Changyang County, Gufu town of Xingshan County and Muyang River of Yiling County in Yichang City of western Hubei Province, central China (Fig. 3). It grows on rocks of roadsides, especially in fissures filled with soil, at an elevation of ca. 100-280 m.
Chinese name. Yi-chang-jing-tian (宜昌景天). Etymology. The specific epithet of this new species is dedicated to the Yichang city. Taxonomic notes. Sedum ichangensis belongs to Sedum sect. Filipes on account of its carpels adaxially not gibbous, its spurless leaf base and its white flowers (Fu and Ohba 2001). Sedum ichangensis is a species easily identifiable by its floral, stem and leaf features. The new species resembles S. elatinoides in the leaf characters, as well as the structure of the flowers. However, S. ichangensis differs from S. elatinoides in its perennial habit with branched stems and its solitary flowers. Sedum ichangensis differs from S. rosthornianum in its much branched, decumbent stems, entire leaf margins and its solitary flowers. Here, we provide photographs (Fig. 1), line drawings (Fig. 2) and a detailed morphological comparison (Table 1) Conservation status. Based on field investigations, S. ichangensis occurs only in three scattered areas. The total area of occupancy is less than 500 km 2 ; each population possesses no more than 300 mature individuals. It prefers habitats on rocks along roads. Human activities are impairing its populations severely. The type population, which grew close to a road, was seriously impacted in its survival due to herbicide spraying in 2018. Based on currently available information, the conservation status of this species is categorised as Endangered [EN] following the IUCN Categories and Criteria (IUCN 2017).