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The conservation status of orchids in the city-state of Singapore mirrors the worldwide decline of this group of plants, one of the largest families of flowering plants.Despite this, the number of extant native orchids has been revised from 45 to 76 in the last 15 years largely due to taxonomic revisions and (re-)discoveries. Building on the history of orchid taxonomic research in the Singapore Botanic Gardens and the revival of plant systematics in Singapore, these recent successes reflect efforts in establishing resident taxonomists and field ecologists, embracing integrative taxonomy, undertaking comprehensive botanical surveys, and developing an opportunistic instinct to discover orchids in the field. Coupled with ongoing species recovery efforts, this provides a sense of optimism for conservation and suggests that small habitat fragments characteristic of cities could continue to be refugia for native orchids. This also further illustrates the important role that botanic gardens play in the conservation of endangered plant species

Many names in the Euphorbiaceae, Phyllanthaceae, Picrodendraceae, Rutaceae and Sapindaceae are lecto- or neotypified. In some cases, these typifications have also enabled the resolution of nomenclatural problems (in Acer laurinum Hassk., Baccaurea racemosa (Reinw.) Müll.Arg., Dimocarpus lichi Lour.). The status of Nymphanthus glaucescens (Miq.) R.W.Bouman (Phyllanthaceae) is reassessed as cryptogenic in Singapore

A few taxonomic and nomenclatural aspects of the genus Oberonia Lindl. relating to the Flora of Singapore are resolved. First, no subgeneric names are recognised in the genus Oberonia. Oberonia subg./sect. Apothemnophyllum Schltr. and Oberonia subg./sect. Menophyllum are synonyms of Oberonia s.s. The autonymous subgenus is a non-mandatory rank, hence, can be omitted. Second, Oberonia hamadryas Ridl. is the correct name for O. scortechinii Hook.f., and the lectotype of Hippeophyllum is here corrected to Hippeophyllum micranthum Schltr. Third, additional species-level synonyms are established for O. equitans (G.Forst.) Mutel (O. hispidula Ames, syn. nov.), O. lunata (Blume) Lindl. (O. wenzelii Ames, syn. nov.), and O. jenkinsiana (O. austro-yunannensis S.C.Chen & Z.H.Ji, O. clarkei Hook.f., O. elbertii Ridl., O. flabellifera Holttum, O. multidentata Aver., O. polyschista Schltr., O.quadridentata Aver., O. rhizophoreti Schltr., O. stenophylla Ridl., O. sumatrana Schltr., O. sumatrana var. endertii Ridl., syn. nov.). Fourth, the specimen K000943003 is here designated as second-step lectotype of Oberonia biaurita Hook.f., and simultaneously also as epitype of O. lunata.

Two species of Phytocrene Wall. are recorded for Singapore: the widespread and commonly collected species P. bracteata Wall., and P. oblonga Wall., known from a single collection from Nee Soon Swamp Forest in the Central Catchment Nature Reserve. Phytocrene bracteata is also cultivated in Singapore Botanic Gardens. The typification of each name is addressed, and a key to the two species, descriptions, an illustration of P. oblonga as well as photographs of both species are provided.

Further work on the genus Piper L. in Singapore has led to the need for a number of nomenclatural and taxonomic clarifications. Lectotypes are designated for ten names: Piper flavimarginatum C.DC., P. pachyphyllum Hook.f., P. crassipes Korth. ex Miq., Cubeba neesii Miq., P. burkillii Ridl., P. lanceolatum Roxb., P. ridleyi C.DC., P. velutibracteum C.DC., P. rostratum Roxb., and P. sarmentosum Roxb. A neotype is designated for P. latifolium W.Hunter, and previous confusion in the literature is clarified.

Bulbophyllum bonjolianum Yudistira, Candra & Mustaqim, a member of section Macrocaulia, is described here based on a specimen collected from the mountains of West Sumatra. It is similar to B. tristriatum Carr. and B. pyridion J.J.Verm. but differs in the morphology of the dorsal sepal, petal and labellum. A key to B. bonjolianum and morphologically similar species is presented.

Two species of Cryptocarya R.Br. are newly described for New Guinea. Both are shrubby to subarborescent lowland species bearing large leaves. Cryptocarya azurea Ezedin is described from the Sepik-Ramu basins, separated out from material formerly identified as C. magnifolia Teshner, whereas C. hydrantha Ezedin, recorded from Jayapura to Josephstaal, is validated based on an unpublished name.

A new species of Primulina Hance (Gesneriaceae), P. serina F.Wen & W.C.Chou from northern Guangxi, China, is described and illustrated. It is morphologically similar to P. versicolor F.Wen, B.Pan & B.M.Wang, but can be easily distinguished by its smaller bracts. In its natural habitat, this species exists only in two subpopulations, and they occupy an area of less than 40 m2 and, following IUCN guidelines, this new species is provisionally assessed as Critically Endangered (CR).

Arunachal Pradesh in northeastern India hosts a diverse array of Strobilanthes Blume species. The occurrence of two previously unreported species, Strobilanthes pubiflora J.R.I.Wood and S. paniculiformis J.R.I.Wood, is documented. Strobilanthes siangensis J.R.I.Wood, Gammi & D.Borah is described as new and discussed in detail. A key to similar species is provided for identification purposes. The paper is illustrated with a map and photographs.

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We review the history of plot-based studies of forests in Singapore and their contribution to our understanding of tropical forest ecology, especially of the regenerative capabilities of forest remnants after fragmentation, land-use change, and other disturbances. With this, we describe the establishment of the Long-Term Forest Ecological Monitoring plot network that includes the continued utilisation of sets of recently established, standardised plots along with the re-establishment of a historical set of plots surveyed by a team led by Wong Yew Kwan in 1992, ensuring the plot design is harmonised across the network.

A little-studied orchid genus, Claderia Hook.f., has until now contained just one or two species, Claderia viridiflora Hook.f. and its possible synonym, C. papuana Schltr. We describe a new species from Singapore, which differs from these Claderia in having small, cream-yellow flowers that are nodding and presented in a long, unbranched terminal inflorescence, mostly with two flowers open simultaneously. We name the new species Claderia leontocampus Niissalo. Plants of the new species have been collected or recorded in Sumatra, Peninsular Malaysia and possibly Peninsular Thailand. We carried out population genetics analyses to show distinction between the new species and Claderia viridiflora. The two species occur in the same habitat in Singapore. We used phylogenetic analyses to find out the phylogenetic position of Claderia within Orchidaceae; the genus is here considered to belong to subfamily Epidendroideae Kostel., tribe Epidendreae Lindl., subtribe Claderiinae Szlach. We publish the plastome and ITS sequences of Claderia viridiflora. Two names are lectotypified.

Three species of Vitaceae are newly recorded for Singapore. One of them, Causonis maritima (Jackes) Jackes, is treated here as native, while two of them, Cissus discolor Blume and Cissus repanda Vahl, are presumed to be introduced.

The nomenclature and typification of Pentaphragma Wall. ex G.Don (Pentaphragmataceae) and its Singapore representative are briefly reviewed. A lectotype is designated for the only generic synonym of Pentaphragma, Francfleurya A.Chev. & Gagnep. Four other lectotypifications for names of species or varieties are given, one at the second step.

The nomenclature and typification of Scaevola taccada (Gaertn.) Roxb. and its synonyms are reviewed. In total, nine new lectotypifications are presented.

Three species of Euphorbiaceae are newly recorded for Singapore, two of which (Euphorbia prostrata Aiton and Microstachys corniculata (Vahl) A.Juss. ex Griseb.) are non-native, and one (Croton erythrostachys Hook.f.) is presumed native but nationally extinct. The record of Microstachys corniculata is supposedly new for the continent. A lectotype is designated for Microstachys corniculata.

The nomenclature and typification of the species of Podocarpaceae in Singapore are discussed.

Eleven species of Iguanura are recognised for Peninsular Malaysia, one of them with two varieties. One species is described as new, Iguanura ruthiae Saw. All species are described, and notes on distribution, provisional IUCN conservation assessment and ecology are given. Thirteen taxa are synonymised and all names typified.

Field work in Panglima Sugala, Tawi-Tawi, Philippines, resulted in new country records of Begonia dimorpha S.Julia (sect. Petermannia, Begoniaceae) and Clerodendrum pygmaeum Merr. (sect. Clerodendrum, Lamiaceae), both previously recorded only from Borneo. There are now 162 species of Begonia L. and 18 species of Clerodendrum L. known from the Philippines. Field observations and taxonomic notes on each species are presented and the presence of Bornean plant elements in the Sulu archipelago is discussed.

The genus Hippeophyllum Schltr. is synonymised under Oberonia Lindl. The following names are synonymised under Oberonia scortechinii Hook.f.: Hippeophyllum alboviride J.J.Sm., H. biakense J.J.Sm., H. celebicum Schltr., H. halmaherense J.J.Sm., O. hamadryas Ridl., O. longifolia Ridl., H. micranthum Schtr., H. papillosum Schltr., H. sulense J.J.Sm. and H. wenzelii Ames. Oberonia scortechinii is an epiphyte distributed from Malaysia through Indonesia, the Philippines, to New Guinea and the Solomon Islands at elevations of 0–500 m (rarely to 1000 m).

The genus Gynochthodes Blume (Rubiaceae) in India is revised. Five species are recognised and described, including the new species Gynochthodes nilagiriensis P.Murugan, V.Ravich. & Murugan. Gynochthodes cochinchinensis (DC.) Razafim. & B.Bremer has been recorded for India but is excluded here. All names are typified.

Litsea megamalayana Karupp., V.Ravich. & Bharath (Lauraceae), a new species from the Megamalai Wildlife Sanctuary of the southern Western Ghats, is described and illustrated. A detailed description, illustration, colour photographs and a table of comparisons to an allied species are provided here for easy identification and further study.

A collection made from Nee Soon Swamp Forest in 2005 is confirmed as a specimen of Pycnarrhena fasciculata (Miers) Diels (Menispermaceae). This represents the first record of the genus Pycnarrhena for the native flora of Singapore.

Nomenclatural notes on names of Dipterocarpaceae from Singapore are presented. Four names, including two synonyms, are lectotypified. These are Cotylelobium malayanum Slooten, Dipterocarpus apterus Foxw., Dipterocarpus kerrii King and Vatica maingayi Dyer. The etymology of Dipterocarpus kerrii is discussed.

Nineteen names of Acanthaceae species occurring in Singapore are lectotypified and one name is neotypified

Sindora Miq. is a noteworthy genus in Singapore, with records of its existence, both natural and cultivated, dating back to the colonial period. Among which was the iconic ‘Changi Tree’, an approximately 76 m tall tree at Changi that was felled in 1942 during World War II. With the recent revision of the genus in Singapore, it was timely to survey the key historical landscapes at the Singapore Botanic Gardens (SBG), Fort Canning Park (FCP) and Changi Village Estate (CVE) for Sindora trees that are currently found or were once present in these locations. This was done through a site survey of the three areas, a study of herbarium specimens, literature and pictorial records relating to these areas, and the carbon dating of selected trees to ascertain their ages. At least 26 mature Sindora trees were recorded from this study, with at least 23 from SBG, one from FCP and two from CVE. Eighteen of these trees have been lost over time, leaving a total of eight trees consisting of an individual of Sindora siamensis Teijsm. ex Miq. and five of Sindora wallichii Benth. from SBG, one Sindora siamensis from FCP and one Sindora × changiensis L.M.Choo et al. from CVE. The latter is a hybrid of Sindora coriacea (Baker) Prain and S. echinocalyx Prain, recently elucidated using molecular tools. The identity of the ‘Changi Tree’ could not be fully verified, but it was likely to have been a Sindora echinocalyx based on a herbarium specimen collected from Changi. This study highlights the conservation value of trees in historical landscapes in Singapore, their importance in contributing to the genetic diversity of species in Singapore outside of nature reserves, and their role as a living legacy of Singapore’s rich botanical and horticultural history.

One new species of Hydnocarpus Gaertn. and two new species of Ryparosa Blume from Peninsular Malaysia are described. Hydnocarpus perakensis Pannell is most similar to H. nanus King, but its fruits are larger and the leaves are hairy. Ryparosa suboppositifolia Pannell is most like R. acuminata Merr., but its leaves are not glaucous and it has an indumentum of
white medifixed hairs. Ryparosa reticulata Pannell is also most like R. acuminata Merr., but it differs in its indumentum of numerous adpressed orange-brown T-shaped hairs on the lower leaf surface, the leaves have up to 6 veins that are closer together and less steeply ascending,and the stamen filaments are free, whereas they form a tube in R. acuminata.

Few orchid studies have focused on the satellite islands of Sulawesi, including the Banggai Kepulauan Archipelago. This study aims to understand the diversity of orchid species in Banggai Kepulauan and to add data on the diversity of orchids in Sulawesi. We identified 28 species of orchids from Banggai Kepulauan, of which two are endemic to Sulawesi: Dendrobium jubatum Schuit. & de Vogel and Dendrobium rhodobalion Schltr.; four species are only distributed in the eastern part of Indonesia: Cylindrolobus quadricolor (J.J.Sm.) Rauschert, Dendrobium lanceolatum Gaudich., Dendrobium purpureum Roxb. and Habenaria beccarii Schltr.; three species are new records for Sulawesi: Aphyllorchis acuminata J.J.Sm., Dendrobium acinaciforme Roxb. and Tainia trinervis (Blume) Rchb.f.; and one species is a new record for Banggai Kepulauan: Crepidium resupinatum (G.Forst.) Szlach.

Two new Hoya R.Br. species and a new subspecies, Hoya towutiensis S.Rahayu, R.P.P.Ahmad & Rodda, Hoya mamasa S.Rahayu, R.P.P.Ahmad & Rodda and Hoya mamasa subsp. longicorolla S.Rahayu, R.P.P.Ahmad & Rodda, are described from Sulawesi, Indonesia. A checklist of Hoya of Sulawesi is published, including 30 species and one subspecies, six of
which are newly recorded. Hoya tsiangiana P.T.Li is typified and considered a new synonym of Hoya australis R.Br. ex J.Traill s.l. 

Some new and noteworthy records of spermatophytes in the Wallacea region are presented. These include three new species records in Wallacea for Lasianthus chrysotrichus Lauterb. (Rubiaceae), Medinilla medinilliana (Gaudich.) Fosberg & Sachet (Melastomataceae)and Thottea tomentosa (Blume) Ding Hou (Aristolochiaceae); new collection records for Pandorea pandorana (Andrews) Steenis (Bignoniaceae) for both Sulawesi and Buru (Maluku Archipelago); a new record in Sulawesi for Aeschynanthus amboinensis (Merr.) Mendum (Gesneriaceae); extended distributions in Sulawesi for six species: Ficus lawesii King (Moraceae), Gaultheria celebensis (J.J.Sm.) Kron & P.W.Fritsch (Ericaceae), Gaultheria hendrianiana (Argent) Kron & P.W.Fritsch (Ericaceae), Gaultheria retusa (Sleumer) Kron & P.W.Fritsch (Ericaceae), Calanthe stenocentron (Schltr.) M.W.Chase et al. (Orchidaceae) and Rhododendron torajaense Craven (Ericaceae); and an extended distribution in Maluku for Begonia aptera Blume (Begoniaceae). The morphology of the poorly documented Sulawesi endemic Gaultheria celebensis (J.J.Sm.) Kron & P.W.Fritsch is discussed.

Curcuma lindstromii Škorničk. & Soonthornk. (Zingiberaceae: Zingiberoideae), a new species from Thailand, is described. It is compared to the morphologically closest species from Curcuma subg. Ecomatae, Curcuma rhomba Mood & K.Larsen. A detailed description, a colour plate and information on its distribution, ecology, phenology and uses are provided. A provisional IUCN conservation assessment of Vulnerable is proposed for this species. A lectotype is designated for the name Curcuma stenochila Gagnep.

A new species, Luisia verrucosa Kurzweil, Nob.Tanaka & Ormerod, from Shan State in Myanmar is described and illustrated. It is very distinct in the genus, characterised by (1) light pinkish and purple-marked navicular sepals which are coarsely verrucose on the outside, especially in their distal part, (2) light pinkish and irregularly pink-dotted lorate-elliptic petals with yellow tips, and (3) a lip with a comparatively large, oblong-elliptic, maroon-purple epichile with prominent callosities in the form of massive bulges. Because its lip does not have a constriction or prominent boundary line between hypochile and epichile, it is superficially similar to Luisia brachystachys (Lindl.) Blume, but the new species differs by having considerably larger flowers with verrucose sepals and pronounced lip ornaments.

Found throughout the world, the Rubiaceae is the fourth largest family of angiosperms, with around 605 genera (POWO, 2021) and 13,000 species (Bremer, 2009). It is easily identified in the field by its simple, opposite or whorled, entire leaves, interpetiolar stipules, and gamopetalous flowers with an inferior ovary (Davis et al., 2009). In India, it is represented by 637 taxa (572 species, 14 subspecies, and 51 varieties) (Deb, 2001; Gangopadhyay et al., 2020) of which 130 species are endemic to the Southern Western Ghats (Nayar et al., 2014; Singh et al., 2015). During taxonomic studies on the Rubiaceae in South India, the authors found that 29 names had not yet been typified and a further six had only been partially typified. Therefore, these 35 names are here lectotypified, including six in a second step lectotypification.

Two new species of Syzygium Gaertn. from Sri Lanka, S. aureum Jayasinghe and S. hemachandrae Jayasinghe, are described. Syzygium aureum is distinguished from S. grande (Wight) Walp. in having a thick ring of nectarial glands near the rim of the hypanthium and in having subglobose fruits tinged with red at ripening. Syzygium hemachandrae differs from S. assimile Thwaites in having a longer petiole, an elliptic to ovate-elliptic lamina with fewer lateral veins, a cylindrical to subcylindrical peduncle at its basal parts and approximately quadrangular secondary axes. Syzygium aureum, which was previously misidentified as Syzygium firmum Thwaites (= S. grande), is restricted to the southwestern lowland rainforests, while S. hemachandrae is confined to the moist monsoon forests of the intermediate zone of eastern Sri Lanka. Both new species were found to be included amongst the syntypes of Syzygium assimile. We therefore designate a lectotype and recircumscribe Syzygium assimile.