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The genus Hoya is highly diverse and many of its species are popular ornamental plants. However, the relationships between Hoya and related genera (the Hoya group) are not fully resolved. In this study, we report 20 newly sequenced plastomes of species in the Hoya group. The complete plastomes vary in length from 175,405 to 178,525 bp while the LSCs vary from 90,248 to 92,364 bp and the complete SSCs vary from 2,285 to 2,304 bp, making the SSC in the Hoya group one of the shortest known in the angiosperms. The plastome structure in the Hoya group is characterised by a massive increase in the size of the inverted repeats as compared to the outgroups. In all ingroup species, the IR/SSC boundary moved from ycf1 to ndhF while this was not observed in outgroup taxa, making it a synapomorphy for the Hoya group. We have also assembled the mitogenome of Hoya lithophytica, which, at 718,734 bp, is the longest reported in the family. The phylogenetic analysis using exons from 42 taxa in the Hoya group and three outgoups confirms that the earliest divergent genus in the Hoya group is Papuahoya, followed by Dischidia. The relationship between Dischidia and the clade which includes all Hoya and Oreosparte taxa, is not fully supported. Oreosparte is nested in Hoya making it paraphyletic unless Clemensiella is recognised as a separate genus.

Gordonia penangensis Ridl. is a rainforest tree native to Peninsular Malaysia and Singapore. Here we provide the complete plastome from a collection made in Singapore. The plastome sequence is 156,915 bp long with a large single copy, a small single copy and two inverted repeat regions of length 86,669, 18,200 and 26,023 bp, respectively. A total of 114 unique genes were identified, including 80 coding genes (seven in two copies), four ribosomal RNAs (all in two copies) and 30 transfer RNAs (seven in two copies). The plastome architecture and gene content are very similar to previously published plastomes from genus Polyspora, to which most Asian Gordonia species have been transferred. Phylogenetic analyses using maximum likelihood were carried out on CDS regions from complete plastomes of 88 taxa, including five out of the 43 species currently recognised to be from Polyspora. A nuclear DNA phylogeny based on ITS sequences was also generated. Our results support the view that all Asian species of Gordonia are best treated as Polyspora. Four new combinations, Polyspora penangensis (Ridl.) Niissalo & L.M.Choo, Polyspora singaporeana (Wall. ex Ridl.) Niissalo & L.M.Choo, Polyspora obtusa (Wall. ex Wight) Niissalo & L.M.Choo and Polyspora ovalis (Korth.) Niissalo & L.M.Choo are made. Three lectotypes are also designated here.

Species radiations have long fascinated biologists, but the contribution of adaptation to observed diversity and speciation is still an open question. Here, we explore this question using the clove genus, Syzygium, the world’s largest genus of tree species comprising approximately 1200 species. We dissect Syzygium diversity through shotgun sequencing of 182 distinct species and 58 additional as-yet unidentified taxa, and assess their genetic diversity against a chromosome-level reference genome of the sea apple, Syzygium grande. We show that Syzygium grande shares a whole genome duplication (WGD) event with other Myrtales. Genomic analyses confirm that Syzygium originated in Sahul (Australia-New Guinea), and later diversified eastward to the Hawaiian Islands and westward in multiple independent migration events. The migrations were associated with bursts of speciation events, visible by poorly resolved branches on phylogenies and networks, some of which were likely confounded by incomplete lineage sorting. Clinal genomic variation in some sublineages follows phylogenetic progression, which coupled with sympatric occurrences of distantly related species suggests that both geographic and ecological speciation have been important in the diversification of Syzygium. Together, these results point to a mixture of both neutral and adaptive drivers having contributed to the radiation of the genus.

The abundance of apomixis in tropical plant genera is poorly understood, and this affects the understanding of speciation and evolution. Hanguanaceae is a tropical monogeneric, dioecious plant family. All but two species are solitary herbs with no capability to spread vegetatively. Viable seeds are often produced when males have not been observed. Our aim was to investigate the presence of apomixis in Hanguana. We used reduced representation genomics to study phylogenetics and genetic variability in all populations of Hanguana in Singapore. We measured genome sizes and estimated ploidy levels in 10 species. Almost all taxa tested were genetically uniform (uniclonal) regardless of the extent of their distribution. The distribution of single clones over distinct localities supports our hypothesis of apomictic reproduction. Only one sexually reproducing native species was detected. Triploid and pentaploid states support our hypothesis that the type of apomixis in Hanguana is gametophytic. Population genomics tools offer a quick and cost-effective way of detecting excess clonality and thereby inferring apomixis. In the case of Hanguana, the presence of male plants is a strong indicator of sexual reproduction, whereas genome triplication is indicative of apomictic reproduction., We used reduced representation genomics to observe population diversity in the dioecious herb genus Hanguana in Singapore. Our results suggest that most of the studied species reproduce exclusively via apomictic seeds, and form populations that are composed of single, widely distributed clones. This explains a lack of records of male plants in the area. The relationships of apomictic clones to sexual populations, for example possible hybridization, require further study. Apomictic clones of Hanguana are associated with uneven ploidy levels.

The city-state of Singapore continues to provide many new records and rediscoveries of plant species in its nature reserves, offshore islands and secondary forests. Eleven new records for Singapore an

Hanguana podzolicola (Hanguanaceae) is newly recorded for Singapore. Detailed colour plates are given alongside the main characters for distinguishing this species from the two most similar species in

The correct understanding of early historical names in Hanguana is essential to facilitate taxonomic progress in this rich and widespread but taxonomically challenging group. The history of two often confused early names, Hanguana malayana and H. anthelminthica, is presented, and their identities are clarified. Hanguana malayana, a name previously applied on wide array of species across SE Asia, needs to be applied to a critically endangered solitary forest species so far confined to Penang Island, Peninsular Malaysia. A neotype is proposed for H. malayana. A lectotype is selected for H. anthelminthica, a name which has to be applied to a widely distributed stoloniferous helophyte originally described from Java. A description and a colour plate of Hanguana malayana are provided, and references to recent description and colour plates of Hanguana anthelminthica, misinterpreted in recent works as H. malayana, are given. The identity of Hanguana aquatica, treated here as a synonym of Hanguana anthelminthica, is also discussed, and the lectotype is designated. In addition, original material for the only other two early names, Hanguana kassintu and Susum minus, was located and lectotypes are designated. A new combination, Hanguana minus, is proposed here.

Recent molecular phylogenetic studies have shown that Hoya is paraphyletic without Absolmsia, Clemensiella, Madangia, and Micholitzia. These genera have been placed in synonymy with Hoya, but the monophyly of Hoya sensu lato relative to other genera of the broader Hoya group (Dischidia, Anatropanthus and Oreosparte, the latter two never included in a molecular phylogenetic analysis) remained unclear. Furthermore, no analysis has included both a significant sample of the Hoya group and outgroup genera of Marsdenieae to test the monophyly of the Hoya group and its position within the tribe. To address these gaps, we assembled two data sets: (1) the chloroplast trnT-trnL-trnF locus from 110 species and (2) three chloroplast loci (trnT-trnL-trnF, atpB-psbA spacer and matK) and two nuclear loci (nrDNA ITS and ETS) from 54 species. The Hoya group is monophyletic and nested in an Asian/Australian clade of Marsdenia s.l. The genus Hoya is paraphyletic unless Anatropanthus, Dischidia and Oreosparte are included. However, current evidence is not sufficient to synonymize Dischidia and Oreosparte with Hoya. Support for synonymy of Anatropanthus with Hoya is strong and the new name H. insularis is proposed. A clade of three new species with Oreosparte-like morphology is sister to the rest of the Hoya group and is described as the new genus Papuahoya.Citation: Rodda M., Simonsson N., Ercole E., Khew G., Niissalo M., Rahayu S. & Livshultz T. 2020: Phylogenetic studies in the Hoya group (Apocynaceae, Marsdenieae): the position of Anatropanthus and Oreosparte. – Willdenowia 50: 119–138. doi: https://doi.org/10.3372/wi.50.50112Version of record first published online on 27 March 2020 ahead of inclusion in April 2020 issue.

PREMISE OF THE STUDY Tropical plant communities in fragmented forests are likely to experience an extinction debt, i.e., the habitat cannot support as many species as are present due to reduced habitat size and connectivity. There are few estimates of the number of species that represent extinction debt, and the number of extinctions over time has rarely been recorded. We recorded population sizes to assess threats and extinctions in gingers (sensu Zingiberales) in fragmented rainforest in Singapore, ca. 200 yr after fragmentation began. METHODS We surveyed extant diversity and population sizes of gingers and used the results to estimate species survival. We critically assessed historic specimens to estimate initial extinctions and extinctions realized in present habitats. KEY RESULTS We recorded 23 species, including five species previously presumed nationally extinct and four species omitted from the national checklist. The revised extinction rate is much lower than previously reported (12 vs. 37%). Most gingers have very small populations or miniscule ranges, implying that extinction debt has not been paid off. CONCLUSIONS Ginger diversity remains high, but the number of species at immediate risk of extinction outnumber recorded extinctions. Although tropical forest fragments remain arks of plant diversity for a long time, extinction debt may be prevalent in all plant groups in Singapore. Slow relaxation of extinction debt should be explicitly identified as a conservation challenge and opportunity. For conserving plant diversity in tropical fragments, relaxation must be reversed through restoration of degraded landscapes and, where feasible, targeted ex situ conservation and planting.

As deforestation and urbanization continue at rapid rates in tropical regions, urban forest patches are essential repositories of biodiversity. However, almost nothing is known about gene flow of forest-dependent tree species in urban landscapes. In this study, we investigated gene flow in the insect-pollinated, wind-dispersed tropical tree Koompassia malaccensis in and among three remnant forest patches in the urbanized landscape of Singapore. We genotyped the vast majority of adults (N=179) and a large number of recruits (N=2103) with 8 highly polymorphic microsatellite markers. Spatial genetic structure of the recruit and adult cohorts was significant, showing routine gene dispersal distances of ~100–400 m. Parentage analysis showed that 97% of recruits were within 100 m of their mother tree, and a high frequency of relatively short-distance pollen dispersal (median ~143–187 m). Despite routine seed and pollen dispersal distances of within a few hundred meters, interpatch gene flow occurred between all patches and was dominated by pollen movement: parentage analysis showed 76 pollen versus 2 seed interpatch dispersal events, and the seedling neighborhood model estimated ~1–6% seed immigration and ~21–46% pollen immigration rates, depending on patch. In addition, the smallest patch (containing five adult K. malaccensis trees) was entirely surrounded by >2.5 km of ‘impervious’ substrate, yet had the highest proportional pollen and seed immigration estimates of any patch. Hence, contrary to our hypothesis, insect-mediated gene flow persisted across an urban landscape, and several of our results also parallel key findings from insect-pollinated canopy trees sampled in mixed agricultural–forest landscapes.

An illustrated revision of Marantaceae in Singapore with an identification key and proposed national IUCN Red List assessments is presented here. In total three genera and four species are considered native to Singapore ( Donax canniformis , Phrynium hirtum , Stachyphrynium parvum , and Stachyphrynium latifolium ) representing 33 % of diversity currently known to occur in Peninsular Malaysia. Although the genus Phrynium Willdenow (1797: 1) was previously reported for Singapore based on the presence of P. villosulum , we show that this species is, contrary to previous accounts, not native but introduced. Newly reported Phrynium hirtum therefore represents a new native generic record for the country. We are changing the status of Schumannianthus benthamianus , previously considered native, to cultivated, as there are no historic or recent collections of this species. Non-native species commonly employed in Singapore streetscapes and parks are also briefly discussed and illustrated in this paper. Actoplanes ridleyi , Donax grandis , Donax parviflora , Maranta tonchat , Phrynium latifolium and Phrynium sumatranum are lectotypified and Maranta arundinacea Blanco (non L.) is neotypified.

A new species of Hanguana (Hanguanaceae), H. thailandica, is described and illustrated from Trang province, Peninsular Thailand. This is the second Hanguana species recorded in Thailand, along with the widespread helophytic H. malayana. The species is morphologically similar to Hanguana exultans and H. nitens found in swamp forests habitats in southern Peninsular Malaysia and Singapore. The conservation status of this species is accessed as Endangered according to the IUCN Red List Category and Criteria.

We describe and illustrate a new species, Hanguana neglecta (Commelinales, Hanguanaceae), from the Bukit Timah Nature Reserve in Singapore, one of the most heavily collected and frequently visited forests in the world. The species, growing prominently near the path at the nature reserve, was not described despite being identified as new fifteen years ago, owing to long-standing taxonomic misconceptions in Hanguana. The key to Hanguana in Peninsular Malaysia is here updated.