Sindora stipitata (Detarioideae, Leguminosae), a new species from Thailand

Abstract Sindora stipitata, a new species in the subfamily Detarioideae (Leguminosae), collected from Nakhon Phanom Province, Thailand, is described and illustrated. The new species is morphologically similar to S. leiocarpa but differs in its smaller stature (3–5 m high), 6-foliolate paripinnate leaves, falcate persistent stipules, presence of a petal auricle, absence of a petal claw, stipitate ovary and capitate stigma. A key to the Thailand and Malesia species of Sindora is provided.


Introduction
Sindora Miq. is a genus in the tribe Detarieae (Detarioideae: Leguminosae) (McKinder 2005). It consists of 18-20 species distributed in Southeast Asia, one in Africa (Larsen et al. 1984, Lock and Heald 1994, McKinder 2005, two species in the South Asia (Kumar and Sane 2003) and two species in China (Chen et al. 2010). Three species have been identified in Thailand. Of these, S. siamensis Teysmann ex Miq. is a very common species of dry deciduous dipterocarp forests and beach forests, especially the type variety (Larsen et al. 1984).
During floristic surveys in the years 2009 to 2016 in the northeast of Thailand, a specimen of Sindora was collected from the Phulangka National Park in Nakhon Phanom Province which, on further investigation, was found to be clearly different from the previously reported species. It closely resembled S. leiocarpa Backer ex de Wit from Malesia. This was confirmed after comparing it against the type and description of S. leiocarpa and is here described as a new species.

Materials and methods
Morphological characters were studied based on living plants observed during a field trip in the northeast of Thailand in the years 2009 to 2016 and from dried herbarium specimens housed in BKF and K. The studies consulted all relevant taxonomic literature in Thailand and neighbouring countries. Measurements were made using a vernier caliper and were examined under a stereo dissecting microscope. The conservation status of the new species was evaluated based on the guidelines of the International Union for Conservation of Nature (IUCN 2017). Diagnosis. Sindora stipitata is very similar to S. leiocarpa from Malesia, but it is easily distinguished by the following characters: a smaller stature (3-5 m high), 6-foliolate paripinnate leaves, falcate persistent stipules, presence of a petal auricle, absence of a petal claw, stipitate ovary and capitate stigma.
Preliminary conservation status. Sindora stipitata is known only from the type locality and its estimated extent of occurrence is less than 100 km 2 . The number of mature individuals was less than 1,000 and the occupied area is continuing to decline slightly. Therefore, it should be considered as "Critically Endangered" according to the IUCN criteria B1 (IUCN 2017).
Discussion. Sindora stipitata is closely related to S. leiocarpa, a plant that grows in Sumatra (Jimbi, Palembang and Riau) and Borneo (Sarawak, Brunei, Sabah and Kalimantan) (Hou 2000), but is easily distinguished from the latter by several morphological characters. Details of the differences between S. stipitata and S. leiocarpa are presented in Table 1.
The new species is also related to S. coriacea (Baker) Prain. Both have unarmed sepals, but S. stipitata is clearly different from S. coriacea by its stature of a small tree (3-5 m high) (vs. a large tree up to 50 m high), its abaxial leaflet surface dull brown (vs. shining), the two largest stamen 22-25 mm long (vs. ca. 10 mm long) and anthers 5.5-6 mm long (vs. 2-3 mm long). The new species also clearly differs from S. laotica Gagnep., a species that is distributed near the border of Thailand (in Vientiane, Phou Khao Khouay National Biodiversity Conservation Area, Lao) and Vietnam (Larsen, Larsen and Vidal 1980); the two species are different in that there is no spiny outgrowth on the outer surface of the calyx of the new species (vs. calyx spinescent). The following identification key for Sindora in Thailand and Malesia is constructed by modification of the key from the Flora Malesiana (Hou 2000).