IMPATIENS ROSTRATA (BALSAMINACEAE), A NEW SPECIES FROM KHAMMOUANE PROVINCE, LAOS, AND NINE NEW RECORDS

One new species, Impatiens rostrata Souvann. & Lanors., is described and illustrated, and nine new records of Impatiens for Laos are reported. A lectotype of Impatiens rubrostriata Hook.f. is designated, and two new synonyms are made.


Introduction
Impatiens L. (Balsaminaceae) was established by Linnaeus (1753) to accommodate Impatiens chinensis L. (the lectotype species), a tiny plant collected in China and also common in the Lao People's Democratic Republic (Laos). There are more than 1500 species in the genus worldwide (Suksathan & Triboun, 2009;Cho et al., 2017;Ruchisansakun et al., 2018), but it is difficult at present to give an accurate number of the species found in Laos because there has not been a taxonomic revision of the Balsaminaceae of Laos since Hooker's contribution to Lecomte's Flore générale de l' Indo-Chine (1911). Hooker treated only four species that were clearly from Laos and another four from Stung Treng, which was in Laos in the early twentieth century. Species found in Stung Treng, which is now in Cambodia, are likely to occur in Champasak Province, Laos.
Distribution. Central Laos, Khammouane Province, Mahaxay District, Phou Hin Poun National Protected Area. Phenology. Flowering during the rainy season, from July to September; fruiting late July to October.
Etymology. The epithet is from the Latin, rostratus, meaning 'beaked', referring to the beak-shaped spur.
Proposed IUCN category. Least Concern (LC). Impatiens rostrata is currently known only from the type locality within Phou Hin Poun National Protected Area, restricted to a single locality where the population comprises c.30 individuals. Phou Hin Poun National Protected Area measures 1690 km 2 , and this can be taken as the extent of occurrence. The area of occupancy is 4 km 2 , but this is likely to be an underestimate. Because the whole distribution of Impatiens rostrata is within a National Protected Area, it must be assessed as LC at present. It should be noted, however, that this is a limestone area and mining for cement manufacture may be tolerated, even if it is not strictly legal. For this reason, the locality should be frequently monitored for damage.
The new species belongs to Impatiens sect. Semeiocardium, a large group that includes c.70 species in Southeast Asia (Yu et al., 2015), all with connate lateral united petals.   Distribution. This species occurs in Louangphabang Province, close to the type locality in Phitsanulok, Thailand, and in Yunnan Province, China, where it was originally described under Impatiens wenshanensis (Huang, 2003).
Habitat and ecology. Impatiens damrongii was found growing in shaded and mixed bamboo to deciduous forest in limestone areas, 300-500 m altitude, associated with Amorphophallus sp. ( Vegetatively, this species is close to Impatiens clavigera Hook.f. but differs in having dentate-glandulate outer lateral sepal margins and a large thick crest in the dorsal petal. The type drawing and original description of Impatiens wenshanensis match the protologue of I. damrongii well.  Ruchisansakun et al., 2018). Figure 3D-F.

Impatiens drepanophora
Distribution. This species occurs in Xiengkhouang and Houaphane Provinces in northern Laos. It was originally described from the Khasia Hills in Northeast India and has also been reported from Nepal, South China and Myanmar (Ruchisansakun et al., 2018).
Habitat and ecology. Impatiens drepanophora was found growing in evergreen montane forest in moist soil near streams, 900-1800 m altitude, associated with ferns. Distribution. This species has been found at Phou Chom Voy, Khamkeut District, Bolikhamxai Province, Laos. It was originally described from central Myanmar (Toppin, 1920) and has also been reported from China and Vietnam (Chen et al., 2007;Chinh et al., 2015).  Ruchisansakun et al. (2018) to have pink flowers because of the very pale pink petals in the type specimen, which differs from the colour indicated in the protologue (yellowish white). We feel that the colour described in the text of the protologue is more reliable than what we have seen on a 100-year-old specimen. Our material varies from the type specimens by having yellow flowers (not yellowish white). This concept is also adopted in the Flora of China (Chen et al., 2007). Impatiens kamtilongensis also resembles I. wuchengyihii S.Akiyama, H.Ohba & S.K.Wu from South China morphologically but differs by the shape of the lateral sepals (ovatelanceolate versus linear). It also differs from Impatiens phahompokensis T.Shimizu & Suksathan from Thailand by its inflorescences with 1 or 2 flowers versus solitary flowers, and its lateral sepals, which are ovate, not suborbicular.  Ruchisansakun et al., 2018).  Distribution. This species has now been discovered in Louangphabang Province, northern Laos. It was originally described from Thailand by Craib (1926) and has also been reported from Myanmar (Ruchisansakun et al., 2018). Vegetatively, this species is close to Impatiens parishii Hook.f. but differs in having the pedicel as long as or longer than the petiole (versus much shorter than petiole); the lateral united petals are grooved with orange to red mixed with yellow (versus flat and only with a yellow patch at the middle). It usually grows at high elevation in open limestone areas, whereas Impatiens parishii grows at low elevation, 300-500 m.  Ruchisansakun et al., 2018). Figure 5D-F.

Impatiens lobbiana
Distribution. This species has been found on karst limestone in Vangvieng, Vientiane Province, central Laos. The original description was based on material collected in Myanmar (Ruchisansakun et al., 2018).
Habitat and ecology. Impatiens lobbiana was found growing at the foot of a limestone hill near a stream in the mountains. It was growing in wet soil in primary evergreen valley forest at altitude c.300 m.
Phenology. Flowering from June to August, fruiting from July to October. Impatiens lobbiana is very similar to I. spectabilis Triboun & Suksathan but differs in having the upper lateral petals obcordate (versus emarginate to obtuse) and dorsal petals obcordate (versus obovate). Our material differs from the type specimens by its larger, ovate lower petal that is broader than the upper petal, whereas the type has oblong to obovate lower petals that are narrower than the upper petals. However, more molecular studies are needed to reveal their true relationship.   Nguyen et al., 2018). Figure 4D-F.
Distribution. This species has been found in Xiengkhouang Province, northern Laos. The original description was based on type material collected in Guangxi, China (Chen, 2000), and the species has also been reported from Vietnam (Nguyen et al., 2018).
Habitat and ecology. Impatiens napoensis was found growing in moist soil in primary evergreen forest, on a mountain slope in a valley at 1800 m altitude on Phou Sam Soum near the border between Khoun and Mok Districts.

Impatiens parishii
Distribution. This species has been discovered in Louangphabang Province, northern Laos. The original description was based on material from Myanmar, and it has also been reported from Thailand (Ruchisansakun et al., 2018).
Habitat and ecology. Impatiens parishii was found growing on a limestone hill in humid mixed deciduous forest at an altitude of 500 m. In the dry season, only stems are present, and leaves develop in the rainy season. This species is very attractive and grows on limestone rock with Draceana sp. (Asparagaceae).
Phenology. Flowering from May to October, fruiting from September to November. Impatiens parishii is very close to I. kerriae Craib but differs in having the pedicel shorter than the petioles (versus pedicel longer than petioles), lateral sepals pinkish to white, without spot (versus orange spot at midvein or nearby), and lateral united petals flat with yellow patch (versus grooved with orange-yellow to red patch). Impatiens parishii grows at low altitude near the Mekong river in Laos, whereas I. kerriae grows near the summits of limestone mountains in open areas.  Figure 5A-C.

Impatiens rubrostriata
Distribution. This species has been found on Phou San in Xiengkhouang Province, northern Laos. The original description was based on material from Guangxi, China (Hooker, 1911).
Habitat and ecology. Impatiens rubrostriata was found growing by streams in moist sandy soil in primary evergreen forest, in mountain valleys at 1800-2200 m altitude on Phou San and Phou Sam Soum.
Phenology. Flowering from August to November, fruiting estimated to take place from October to December. Impatiens rubrostriata is similar to I. duclouxii Hook.f. but differs in having white flowers with red stripes on the lateral united petals (versus entirely yellow flowers), and the lateral sepals being larger and white with a red spot or entirely red (versus lateral sepals smaller and greenish to yellow).