Perrottetiataronensis B.M.Barthol. & K.Armstr., sp. nov. (Dipentodontaceae), a new species from northwestern Yunnan Province, China and northern Kachin State, Myanmar and a re-examination of the Asian and Australasian taxa of Perrottetia

Abstract Perrottetiataronensis from the Dulong Jiang valley in northwestern Yunnan Province, China and the Babulongtan mountain range in northern Kachin State, Myanmar is here described as a new species of the Dipentodontaceae. It is the third species of the genus to be recognized for China and the first to be reported for Myanmar. It is similar to P.alpestriss.s. but differs by characters of its leaf margins, inflorescences, and fruit. The three subspecies of P.alpestris recognized by Hou in “Flora Malesiana” are here recognized as three distinct species, i.e., P.alpestris, P.moluccana, and P.philippinensis on the basis of differences in diagnostic characters and distribution. The report in the “Flora of China” of the Taiwan species P.arisanensis from Yunnan is determined to be incorrect due to misidentification of two specimens at KUN.


Introduction
Perrottetia Kunth is a genus of about twenty species occurring mainly in tropical America and tropical Asia. In addition, two species are endemic to the Hawaiian Islands (Lorence and Wagner 2019). The genus was formerly included in Celastraceae, but evidence from nuclear and plastid genes supports its placement in Dipentodontaceae (Zhang and Simmons 2006), now treated as a separate family in the order Huerteales (Chase et al. 2016). Dipentodontaceae has two genera, Perrottetia and the monospecific genus Dipentodon Dunn (Ma and Bartholomew 2008). In the Old World Perrottetia occurs from mainland Asia south to New Guinea and northeastern Australia, east to the southwest Pacific islands, and north to China and Myanmar. In the "Flora of China" two species were reported (Ma and Bartholomew 2008). One of these, P. racemosa (Oliv.) Loes., is widely distributed in southern and southwestern China (Ma and Bartholomew 2008), occurring in the provinces of Guangxi, Guizhou, SW Hubei, NW Hunan, Sichuan, and S-SE Yunnan as well as the Chongqing Municipality which was formerly the eastern part of Sichuan Province. Perrottetia racemosa was first described as an Ilex L. by Oliver (1889) on the basis of collections made by A. Henry in Hubei Province, China, but was later transferred to Perrottetia by Loesner (1892). The other species in China, P. arisanensis Hayata (1915), was described from Taiwan Province. Recently, a third species has been found in China and Myanmar and is reported here in China from northwestern Yunnan Province in the Dulong Jiang valley of Gongshan Xian and in Myanmar from Kachin State in Putao District. This new species is similar to P. alpestris (Blume) Loesn. s.s. but differs by several characters given below in the discussion and the key to the Asian and Australasian species of Perrottetia. It is also disjunct from P. alpestris s.s. by over 2500 km.
The "Flora of China" treatment of Perrottetia reported that P. arisanensis not only occurs in Taiwan but also in central Yunnan in Eshan Xian 峨山县 and southeastern Yunnan in Xichou Xian 西畴县 (Ma and Bartholomew 2008). This Yunnan distribution is, however, incorrect as it was based on the misidentification of two specimens at KUN. The specimen from Eshan Xian (Yuxi Team 玉溪队 89-256 collected 7 July 1989) has been redetermined to be a Rhamnus L., and the specimen from Xichou Xian (Wu Quanan 武全安 7981 collected 7 May 1959) has been redetermined to be P. racemosa. With this correction, P. arisanensis is endemic to Taiwan. Diagnosis. Perrottetia taronensis is similar morphologically to P. alpestris s.s. (see Discussion) from which it differs by having much more compact and shorter inflorescences which are sparsely golden tan-tomentose rather than sparsely reddish browntomentose, a shorter stipe, leaf margins that are sharply serrate rather than bluntly serrate, and larger fruit when mature.
Etymology. The specific epithet "taronensis" refers to the Taron River valley in Myanmar. In China this river is named the Dulong Jiang (Dulong River) (Fig. 4). The Taron River flows into the N'Mai Hka (N'Mai River) which joins the Mali Hka (Mali River) forming one of the main northern tributaries of the Ayeyarwady River (Irrawaddy River).
Habitat and distribution. The seven collections of Perrottetia taronensis that have so far been made occur in the Ayeyarwady River drainage in both Yunnan Province, China and Kachin State, Myanmar at an elevation range of 1350-1970 m (Fig. 4). In China P. taronensis occurs on slopes in subtropical broadleaved evergreen forests, in disturbed secondary forests of Alnus nepalensis D. Don (an early successional tree species of secondary forests in this region), and among shrubs near river banks. In Myanmar, the habitat of the single collection of a male plant is classified within the Kachin Hills subtropical rainforest ecosystem, a closed-canopy humid lower montane forest type occurring between In Myanmar, the single collection is from the Babulongtan mountain range, in the drainage of the Nam Tisang/Mali Hka, which is in the adjacent river system to the west of the N'Mai Hka.
Proposed IUCN Conservation Status. The proposed Conservation Status of Perrottetia taronensis is Endangered (EN), B1ab(i,ii,iii,v)+2ab(I,ii,iii,v), according to the IUCN Standards and Petitions Committee (2019). This status is based on the criteria of EOO 802.498 km 2 and AOO 319.308 km 2 calculated by using GEOCAT (Bachman et al. 2011) and due to the occurrence in a small area, a decline in the quality of its habitat, and the low number of mature individuals observed.

Discussion
As treated here Perrottetia is now known in Asia and Australasia as having six species of which three occur in China and one in Myanmar. The genus is herein recorded for the first time from Myanmar as it was not mentioned in either Merrill's (1941) list of "Upper Burma Plants" or in Kress et al.'s (2003) country-wide checklist. On the basis of the single Myanmar collection being a male plant and all six Chinese collections made so far being female plants in fruit, it is likely that P. taronensis is dioecious. This condition is common in the genus, although additional field studies in the spring during flowering are needed for confirmation.
Perrottetia taronensis is most similar morphologically to P. alpestris s.s. (see below) which occurs in Peninsular Malaysia as well as in Indonesia on Sumatra and Java plus nearby small islands. It differs from P. alpestris s.s. by several characters enumerated in the diagnosis above and in the key to the Asian and Australasian species of Perrottetia below. Moreover, P. taronensis and P. alpestris exhibit a north-south disjunction of about 2500 km, with Perrottetia not recorded from intervening continental Southeast Asia (Hou 1962;Hou et al. 2010).
In addition to Perrottetia alpestris s.s., two other Perrottetia species (P. moluccana (Blume) Loes. and P. philippinensis (S. Vidal) Loes.) occur in Southeast Asia and Australasia. Although treated as species by Loesner (1892), they were treated respectively as P. alpestris subsp. moluccana (Blume) Ding Hou and P. alpestris subsp. philippinensis (S. Vidal) Ding Hou by Hou in the treatment in "Flora Malesiana" (1962). We follow Loesner in treating all three Southeast Asian and Australasian Perrottetia as separate species. Not only do they differ by several diagnostic characters as can be seen in the key to the Asian and Australasian species of Perrottetia below, but also P. alpestris s.s., P. moluccana, and P. philippinensis are disjunct, as was pointed out by Hou (1962). Perrottetia moluccana occurs on the island of New Guinea and the Cape York Peninsula of Queensland Australia, extending into some of the adjacent islands in the southwest Pacific. Perrottetia philippinensis occurs in Indonesia on the islands of Borneo and Sulawesi as well as in the Philippines and on some small adjacent islands. On the basis of diagnostic morphological characters, P. alpestris s.s., P. moluccana, P. philippinensis, and P. taronensis are more similar to each other than this group of four species is to either of the other two Asian species, P. arisanensis and P. racemosa, and these similarities and differences are expressed in the key below. It is hoped that future molecular studies will confirm our interpretation based on diagnostic morphological characters.
We only know of seven collections of Perrottetia taronensis all of which were previously misidentified as Celastrus L. (Celastraceae), Gaultheria L. (Ericaceae), Ilex (Aquifoliaceae), Maesa Forssk. (Primulaceae), or Rhamnus (Rhamnaceae), so it is possible that other specimens are already in herbaria and may come to light, although a search in likely families and genera at KUN as well in the online Chinese Virtual Herbarium (https://www.cvh.ac.cn/) has so far not found additional specimens of this species.