The most distinguishing characteristics that separate Glycosmis (Rutaceae; Aurantioideae; Clauseneae [Kubitzki et al. 2011]) from related genera are its unarmed nature and the rust-colored villosulose indumentum covering young twigs, buds and inflorescences (Swingle and Reece, 1967; Stone, 1985; Jones, 1995; Zhang et al., 2008; Kubitzki et al., 2011). Glycosmis comprises about 52 species mainly distributed in tropical and subtropical Asia and Australia (Zhang et al., 2008; Kubitzki et al., 2011; POWO, 2022). In Thailand, 13 species and two varieties of Glycosmis were reported by Craib (1934), Guillaumin (1946), Stone (1985), and Pooma and Suddee (2014). Three species: G. parva Craib, G. puberula Lindl. ex Oliv. var. subsessilis (Craib) B. C. Stone and G. suberosa H. Toyama & Rueangr. are endemic to Thailand. Five species, including G. chlorosperma (Blume) Spreng. (10–12 m), G. craibii Tanaka (5 m), G. esquirolii (H. Lév.) Tanaka (6–10 m), G. macrophylla (Blume) Miq. (8–10 m), and G. pentaphylla (Retz.) DC. (5 m), have a predominantly dendriform habit (Craib, 1934; Stone, 1978, 1985, 1994; Toyama et al., 2016; POWO, 2022).

During a botanical excursion in Kanchanaburi Province, we encountered a predominant arborescent species of Glycosmis with large leaflets. After we compared the plants with description of the literature (Hooker, 1875; Kurz, 1877; Guillaumin, 1911; Craib, 1934; Stone, 1985; Jones, 1995; Zhang et al., 2008; Pooma and Suddee, 2014; Toyama et al., 2016) and with specimens in herbaria, we were unable to match these plants with any of the known species in the genus. We therefore describe these plants as a new name Glycosmis kanburiensis W. Aiyakool & S. Vajrodaya.

Field excursions were undertaken in March 2017 and February 2018 in Sangklaburi District, Kanchanaburi Province. Specimens were collected using standard procedures for herbarium specimens (Bridson and Forman, 1999). The specimens were mounted on herbarium sheets and deposited in the Bangkok Herbarium (BK) and the Suan Luang Rama IX Royal Botanic Garden (SLR), Thailand.

Morphological characters of vegetative and reproductive parts were examined both in the field and on herbarium specimens. Plant parts were dissected and investigated through use of a stereomicroscope. Photographs of the plants parts were taken and illustrations were made. The morphological comparisons were made using relevant literature (Hooker, 1875; Kurz, 1877; Guillaumin, 1911; Craib, 1934; Stone, 1978, 1985, 1994; Jones, 1995; Zhang et al., 2008; Toyama et al., 2016). The morphology of herbarium collections of closely related species was examined in specimens in BK, BKF, CMU, CMUB, KKU, PSU, QBG, and SING and in high-resolution images of specimen available on the websites of the Kew Herbarium Catalogue (http://apps.kew.org/herbcat/navigator.do), Natural History Museum, London (https://www.nhm.ac.uk/research-curation/scientific-resources/collections/botanical-collections), and the Muséum National d’Histoire Naturelle, Paris (https://science.mnhn.fr/institution/mnhn/collection/). The conservation status was assessed following the criteria given by the IUCN (2019).

Glycosmis kanburiensis W. Aiyakool & S. Vajrodaya, sp. nov.––THAILAND. Kanchanaburi Province: Sangkhla Buri District, Prangphle, 14°58′48.0″N, 98°38′07.3″E, 22 Mar 2017, W. Aiyakool, S. Vajrodaya, N. Wongthet, W. Muangrom, & K. Thaweepanyaporn 179 (holotype: BK [BK No. 082574], isotype: BK, SLR) (Figs. 1, 2).

Diagnosis: Glycosmis kanburiensis is most similar in morphology to G. esquirolii but differs in having triangular sepals covered with rust-colored indumentum (vs. broadly ovate villose sepals), ovary globose and glabrous (vs. subglobose and villose), style cylindrical and attenuate (vs. stout) and fruit ellipsoid (vs. globose).

Trees, evergreen, unarmed, 10–15 m tall, Diameter at breast height (DBH) 1–35 cm. Bark smooth, grayish brown; inner bark white; young branches densely covered with caducous rust-colored indumentum; old branches terete, almost glabrous, whitish brown or grayish brown. Leaves alternate, pinnately compound, 28–42 × 17–35 cm ; petiole 4.5–8 cm long; leaflets 3–9, mostly 5-foliolate, densely covered with caducous rust-colored indumentum when young, glabrous at maturity; petiolules 0.8–1.2 cm long; leaflet blades ovate-lanceolate to elliptic, 18–22 × 8–12 cm, subcoriaceous, abaxial surface grayish-green, adaxial surface dark green, lustrous, base cuneate, margin entire, recurved, apex acuminate or acute-obtuse, pellucid gland-dotted; midrib, prominent abaxially, sunken or almost flat adaxially; secondary veins 7–9 pairs, brochidodromous, faintly prominent adaxially, finely reticulate abaxially; tertiary veins faintly visible on both surfaces. Inflorescences terminal, paniculate, 20–35 cm long, of 3–5 racemes, with many densely arranged flowers; peduncle 4–10 cm long; bracts absent; pedicels absent or to 0.3 cm long, densely covered with rust-colored indumentum. Flowers bisexual, pentamerous; sepals triangular, 2–2.2 × 1.2–1.5 mm, brown, coriaceous, outer surface with rust-colored indumentum, inner surfaces glabrous; petals ovate-elliptic, 8–10 × 2–4 mm, pale yellow or white, subcoriaceous, outer surface with rust colored indumentum, inner surface glabrous, margin entire, apex acute to obtuse, reflexed at anthesis; stamens 10, in two whorls of 5, incurved, stamens in outer whorl antipetalous, longer, 4.5–5.5 mm long, those in inner whorl antisepalous, shorter, 3–4 mm long; filaments of outer whorl longer, 3–3.5 mm long, those of inner whorl shorter, 1.5–1.8 mm long; anthers dorsifixed, 1.8–2 × 0.8–1.2 mm, glabrous, longitudinally dehiscent; disk annular; gynophore 0.2–0.4 cm long, swollen near joint with ovary, glabrous; ovary globose, 5-locular, glabrous, 3.8–4 × 3.5–4.5 mm; style cylindrical, attenuate, 1.5–1.8 mm long, persistent; stigma capitate, ca 0.1 cm long. Fruit berries, oblong-ellipsoid, 3.5–4.8 × 2.8–3.7 cm, greenish, becoming yellowish when ripe, glabrous; seeds 1 or 2, globose-ellipsoid, 2.2–2.8 x 2.0–2.2 cm.

Additional specimen examined: THAILAND. Kanchanaburi: Sangkhla Buri district, Ban Pompi, in bamboo forest, 28 Mar 1967, Prayad Sangkhlachand 724 (BK); ibid, in mixed deciduous forest, 1 Apr 1967, B. Nimanong 12 (BKF).

Phenology: Flowering January to March, fruiting March to May.

Etymology: the specific epithet refers to Kanburi which is a dialectal name of Kanchanaburi Province.

Vernacular name: Khoei Tai Mueang Khan, the name given by us.

Distribution, ecology, and conservation status: Glycosmis kanburiensis is endemic to southwestern Thailand and known only near the type locality in Prangphle and Pompi, Sangkhlaburi District, Kanchanaburi Province (Fig. 3). It is usually scattered in areas with moist substrate near streams or at the base of limestone hills in dry evergreen forests and mixed deciduous forests at 265–400 msl. The major associated species of trees are Dipterocarpus baudii Korth., Swintonia floribunda Griff., Murraya paniculata (L.) Jack., Arenga pinnata (Wurmb) Merr. and Bambusa spp. Glycosmis kanburiensis is preliminarily assessed as Endangered (B1ab(ii), B2ab(ii)) following the criteria of the IUCN (2019). From the known localities in Kanchanaburi Province, the Extent of Occurrence (EOO) is less than 150 km² and the Area of Occupancy (AOO) is about 12 km² at two localities where it is restricted to fragmented small populations of around 10 mature individuals each. They are not within protected areas and may be destroyed by agricultural activities, human disturbance, and tourism.

Note: Glycosmis kanburiensis, our proposed new species from southwestern Thailand, is similar to Glycosmis esquirolii (H. Lév.) Tanaka, of China, Myanmar, and northern Thailand (Appendix 1) in its dendriform habit, large leaflets, and inflorescences seemingly terminal, but differs in having relatively smaller reproductive parts, triangular sepals covered with rust-colored indumentum (vs broadly ovate, villose sepals), petals obovate-elliptic, 8–10 × 2–4 mm and covered with rust-colored indumentum (vs. petals oblong-lanceolate, 4.5–5.5 × 2.5–3 mm and villose), ovary globose, 3.8–4 × 3.5–4 mm and glabrous (vs. ovary subglobose, 1–1.5 × 0.8–1.2 mm long) and villose, style cylindrical, attenuate, 1.5–1.8 mm long (vs. stout, 0.5–1 mm long) and fruit ellipsoid and 3.5–4.8 cm long (vs. globose and 1.5–2.8 cm long) at maturity (Figs. 3, 4).

Glycosmis kanburiensis also resembles G. chlorosperma (Blume) Spreng., G. craibii Tanaka, G. macrophylla (Blume) Miq., and G. pentaphylla (Retz.) DC. However, G. chlorosperma, G. macrophylla and G. pentaphylla have axillary inflorescence, and G. craibii has much smaller subglobose fruit (Table 1). The distinguishing characteristics of G. kanburiensis and related species in Thailand are provided in Table 1.