﻿Resurrection of Drypetesnienkui (Putranjivaceae), endemic to Hainan, China

﻿Abstract Drypetesnienkui (Putranjivaceae), described from Hainan, China, has long been treated as a synonym of D.indica. Both species belong to a distinctive group of Asian species characterized by perulate buds that give rise to shoots bearing flowers or inflorescences proximally and leaves distally, 2–3-carpellate ovaries, and elongate styles. However, D.nienkui fundamentally differs from D.indica in inflorescence architecture and fruiting pedicel length; these or other characters also distinguish D.nienkui from the remaining species in this group. Drypetesnienkui therefore deserves recognition as a distinct species endemic to Hainan. An expanded description of the species is provided along with a key to the related species.


Introduction
The genus Drypetes Vahl (Putranjivaceae Endl., Malpighiales) comprises about 220 species of mostly dioecious trees and shrubs found in the tropics and subtropics worldwide; it is most diverse in Asia, with about 120 species. Thirteen species currently are recognized from China (Qin et al. 2007;Li and Gilbert 2008); of these, nine are reported from Hainan, including the endemic D. longistipitata P.T.Li. Among the currently accepted species found in China, there are two, D. indica (Müll. Arg.) Pax & K.Hoffm., and D. longistipitata, that, along with the Thailand endemic D. dasycarpa (Airy Shaw) Phuph. & Chayamarit, belong to a group of taxa that are distinctive among Asian Drypetes in having prominent buds enclosed in chartaceous scales (perules; Fig. 1A). When the axillary, and sometimes the terminal, buds develop into shoots, the proximal few nodes usually are leafless and produce flowers or inflorescences, while the more distal nodes produce leaves (Fig. 1A). In addition, the pistils, which are 2-3-carpellate, have more or less elongate styles that bear peltate to flabellate stigmas (Fig. 1B); most other Drypetes species in the region have 1-carpellate pistils, sessile stigmas, or both. This group of species, which I will refer to as the D. indica complex, ranges from Bhutan and northeastern India eastward to Taiwan and southward to Thailand. Taxonomic concepts within the Drypetes indica complex have varied widely. For example, Pax and Hoffmann (1922) Shaw (1972), in a review of Euphorbiaceae s.l. in Thailand, synonymized the latter four species under D. indica. He also treated D. nienkui Merr. & Chun, a species described from Hainan, China, as a synonym of D. indica. He noted that this treatment made for a highly variable species, but felt that specimens from Thailand and Hainan bridged the morphological and geographic gaps between Indian/Burman material and that from Taiwan. Li (1988) expanded Airy Shaw's broad concept of D. indica to include D. longipes X.H.Song, and this view has been followed in treatments of the genus for China (Li 1988(Li , 1994Li and Gilbert 2008;Fang et al. 2011). However, Taiwanese botanists have continued to treat the material from there as distinct from D. indica, recognizing either both D. hieranensis and D. karapinensis (Hsieh 1977) or, more recently, synonymizing D. hieranensis under D. karapinensis (Lu 1986;Hsieh et al. 1993;Boufford et al. 2003). Both D. dasycarpa and D. longistipitata were described after Airy Shaw (1972) expanded the concept of D. indica and have consistently been accepted as distinct taxa, although Airy Shaw (1977) initially described D. dasycarpa as a variety of D. indica.
Drypetes nienkui was described from a single fruiting specimen (Merrill and Chun 1935). Because an isotype from this gathering is the only specimen of D. nienkui at K (pers. obs. and GBIF 2022) and I have seen no other specimens of this species annotated by Airy Shaw, it appears that he (Airy Shaw 1972) only saw this specimen before synonymizing D. nienkui under D. indica. Having had the opportunity to examine more specimens, including type material, of D. nienkui and the other species in the D. indica complex from throughout eastern Asia, I believe the broad treatment of D. indica pioneered by Airy Shaw (1972) is too inclusive. Drypetes nienkui, in particular, is quite distinct, although further species may also deserve recognition. Here I review morphological characters that distinguish D. nienkui from D. indica and D. dasycarpa; I also provide an expanded description of D. nienkui and a key to species I currently accept in the D. indica complex.

Materials and methods
Morphological characters were examined on specimens held by A, BM, G, IBSC, K, KUN, L, NY, P, and US (herbarium acronyms follow Thiers [continuously updated]), and online images of specimens from AU, CAS, E, HITBC, IBK, MW, NAS, PE, SN, TAI, TI, and TNM available at JSTOR Global Plants (https://plants.jstor. org/), the Chinese Virtual Herbarium (http://www.cvh.ac.cn/), the Global Biodiversity Information Facility (https://www.gbif.org/), and individual herbarium websites. Measurements were made using both actual specimens and specimen images containing scale bars.

Results and discussion
Material that Airy Shaw (1972) and others included within Drypetes indica exhibits two different inflorescence variants. Specimens from Hainan that have been called D. indica or D. nienkui have staminate and pistillate flowers borne in cymose inflorescences and pistillate pedicels that are no longer than 12 mm in fruit (Fig. 1C), whereas all the remaining specimens of D. indica in the broad sense have fasciculate staminate flowers and solitary pistillate flowers, the pedicels of which become at least 16 mm long in fruit (Fig. 1B); the same is true of D. longistipitata. Merrill and Chun (1935) described the infructescences of D. nienkui as "depauperateracemose" (they had only fruiting material), although they actually are cymose. Drypetes dasycarpa also has cymose inflorescences and relatively short pistillate pedicels, as was reported by Chayamarit (2000, 2005). These inflorescence characters were overlooked by Airy Shaw (1972Shaw ( , 1977, perhaps because the specimens of D. dasycarpa and D. nienkui that he studied at Kew have either only detached fruits or infructescences bearing only a single mature fruit (pers. obs.).
Distribution and habitat. Drypetes nienkui is widespread in the southern half of Hainan, China (see the map for D. indica in Fang et al. [2011], as to Hainan only), occurring in forests at 950-2100 m elevation.
Preliminary conservation status. I have been able to locate only 13 gatherings of Drypetes nienkui. With the exception of two collections made in 2014 and 2017, all the collections date from between 1932 and 1954, but no data are available regarding population sizes or trends. Applying the criteria of IUCN (2022), D. nienkui should receive a preliminary conservation assessment of Data Deficient, although a more complete assessment might show it qualifies as a species of elevated conservation concern.
Key to species in the Drypetes indica complex visits to their institutions. I am grateful to the Naturalis Biodiversity Center for awarding me a Temminck Fellowship, which allowed intensive study of specimens in L. Lynn Gillespie made helpful comments on a draft of the manuscript, and the editor and an anonymous reviewer provided valuable comments and suggestions.