Impatiens bijieensis (Balsaminaceae), a new species from karst plateau in Guizhou, China

Impatiens bijieensis X.X. Bai & L.Y. Ren, sp. nov. from northwest Guizhou Province, China, is described and illustrated. This new species is distributed discontinuously in Jiulongshan, Dafang County and Dajiucaiping, Hezhang County, both of which are in the Wumeng Mountain area, a karst plateau landform. The new species is morphologically similar to I. pterosepala Hook.f., I. lasiophyton Hook.f. and I. leptocaulon Hook.f. in height and flower shape and it especially resembles I. lasiophyton in pilosity. However, it differs in its deep purplish-red flower, 2-lobed lower sepal apex and cylindrical capsule. A detailed description, colour photographs and a provisional IUCN Red List assessment are provided along with discussions of its geographical distribution, ecology and morphological relationships with other similar species.


Introduction
The genus Impatiens Linnaeus (1753: 937), belonging to the Balsaminaceae, consists of more than 1000 species, mainly distributed in the montane forests of the tropics and subtropics of the Old World with five centres of diversity, namely tropical Africa, Madagascar, south India and Sri Lanka, eastern Himalaya and Southeast Asia (Grey-Wilson 1980;Song et al. 2003;Yuan et al. 2004;Mabberley 2017). In recent years, a few new species have also been found in the northern temperate regions of Europe, Russia and China, as well as North America (Liao et al. 2021). Currently, there are more than 349 species of Impatiens in China (Yuan et al., in press) which are distributed mainly in the southwest and northwest mountainous regions, especially in southwest Provinces (including Guizhou, Yunnan, Sichuan) (Chen 2001;Chen et al. 2007;Cai et al. 2015;Kuang 2015;Tan et al. 2015;Ding et al. 2016Ding et al. , 2017Xia et al. 2019;Gu et al. 2021;Liao et al. 2021;Peng et al. 2021b;Song et al. 2021a, b, c) and 61 species of Impatiens have been reported in Guizhou Province (Xiong and Yang 2009;Cong 2010;Kuang et al. 2014;Luo and Deng 2015;Peng et al. 2021a;Yu et al. 2021;Yuan et al. in press).
Impatiens are morphologically characterised by their petals always united in pairs into lateral, united petals; fruit a fleshy, explosive capsule; seeds often dispersed elastically from valves when ripe (Chen et al. 2007). From September 2014 to October 2021, during our field investigation in Bijie City, northwest Guizhou Province, China, we encountered an unknown Impatiens species. The plants were found growing in gullies between gently sloping mountain meadows of karst plateau, this special habitat distinguishing our plants from other known species. After a thorough morphological study, based on literature (Xiong and Luo 1989;Chen 2001;Chen et al. 2007;Yu 2012) and herbarium material (GZAC!), we concluded that this Impatiens species should be placed in I. subg. Impatiens as it differed from previously reported or described taxa and we describe it here as a new species.

Materials and methods
The material for this study was mainly collected from the survey of wild ornamental plant resources in Guizhou Province, China. The morphological description of the new species was based on careful examination of fresh material in the field and herbarium specimens. Comparisons with other species were made to virtual herbarium specimens (GZAC, HC, HIB, IBK, IBSC and PE), photographs and literature (Hooker 1908a;Grey-Wilson 1980;Chen 2001;Chen et al. 2007;Yu 2012).   Diagnosis. Impatiens bijieensis X.X. Bai & L.Y. Ren, sp. nov. is similar to I. pterosepala, I. lasiophyton and I. leptocaulon in plant height, leaf blade shape and flower shape, especially resembling I. lasiophyton in its pilosity and obtuse anther apices, but distinguished by its deep purplish-red flower, linear-lanceolate bract, apex 2-lobed lower sepal and cylindrical capsule.
Etymology. The specific epithet 'bijieensis' refers to the type locality where the new species was found, located in Bijie City, northwest Guizhou Province, China. The Chinese name is given as "毕节凤仙花".
Phenology. Flowers and fruits from August to October. Distribution. Impatiens bijieensis has been observed in Bijie City, Guizhou Province with subpopulations in Hezhang County and Dafang County. We found at Dajiucaiping, Hezhang that the plants grow along the creek on the slopes of gentle hilltops or on the side slope of the ridge, while some were found below the cliffs where water was dripping from streams. At Jiulongshan, Dafang, the population was distributed in evergreen broad-leaved forest margins.
Conservation status. This species is currently known only from Bijie City, Guizhou Province, China with two subpopulations. The Extent of Occurrence (EOO) is less than 100 km 2 and the known Area of Occupancy (AOO) is less than 15 km 2 . The conservation status can be evaluated as Vulnerable (VU) D2, based on the IUCN Red List Categories and Criteria (IUCN 2019). About 150 and 300 individuals were known in the two subpopulations of Hezhang County and Dafang County, both of which are exposed to human disturbance.
Impatiens bijieensis is also similar to I. leptocaulon in the length of its petiole, serrulate leaf blade margin and navicular lower sepal, but differs from its adaxial surface densely pilose and abaxial surface pilose along veins (vs. glabrous), ciliate margined lateral sepals and carinate mid-vein (vs. hyaline margined, denticulate on one side). In order to illustrate the morphological circumscription of this new species, we compare the new species with three species with similar morphological characters in Table 1:  (1908c: t. 2872). Colour photographs of I. bijieensis, I. lasiophyton and I. leptocaulon are given in Fig. 3 and all of them were taken in Guizhou Province. The morphological characters, including perennial habit, racemose inflorescence, 5-carpellate ovary, cylindrical capsule and ellipsoidal seeds, indicate that Impatiens bijieensis is a member of the I. subg. Impatiens. It is known that Impatiens mainly grow in places with high relative temperature and low elevations, yet this new species is found in a karst plateau area that is characterised by its cold climate and high altitude. These ecological characters distinguish it from morphologically-similar species. Additionally, because of the development of tourism, its habitat is currently threatened by human activities.