Species radiations, despite immense phenotypic variation, can be difficult to resolve phylogenetically when genetic change poorly matches the rapidity of diversification. Genomic potential furnished by palaeopolyploidy, and relative roles for adaptation, random drift and hybridisation in the apportionment of genetic variation, remain poorly understood factors. Here, we study these aspects in a model radiation, Syzygium, the most species-rich tree genus worldwide. Genomes of 182 distinct species and 58 unidentified taxa are compared against a chromosome-level reference genome of the sea apple, Syzygium grande. We show that while Syzygium shares an ancient genome doubling event with other Myrtales, little evidence exists for recent polyploidy events. Phylogenomics confirms that Syzygium originated in Australia-New Guinea and diversified in multiple migrations, eastward to the Pacific and westward to India and Africa, in bursts of speciation visible as poorly resolved branches on phylogenies. Furthermore, some sublineages demonstrate genomic clines that recapitulate cladogenetic events, suggesting that stepwise geographic speciation, a neutral process, has been important in Syzygium diversification.

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The plant diversity of Bukit Timah Nature Reserve (BTNR) is relatively well studied due to concerted effort over several decades, particularly as part of the worldwide system of ecological plots set up by the Center for Tropical Forest Science (CTFS), now called the Forest Global Earth Observatory. Publications arising from previous works have set baseline data for the species diversity, suggested that the forest resilience was greater than would be expected in such a small forest fragment, but that there was low recruitment of primary forest tree species into the secondary forest. In order to assess the overall vascular plant diversity, and to compare the diversity of the various forest types within BTNR to each other, 52 plots were set up, each 20 × 5 m, along nine different transects that covered the full range of topography and forest types, primary, old secondary and maturing secondary forests, within the reserve. The vascular plant diversity within each plot was recorded. In total, 1250 species in 148 families were recorded, including an additional 167 species newly listed for BTNR. The primary forest had the highest number of species not found in the other forest types. It nevertheless had a very large overlap with species in the old secondary forest but not with the maturing secondary forest.

Several new records of plant species previously unknown in Singapore are reported, along with records of species presumed to be nationally extinct which have been rediscovered. These reports are based on specimens collected during our recent surveys of the Bukit Timah Nature Reserve and previously unreported older specimens, all deposited in SING. Three species are reported as new records for Singapore: Scindapsus lucens Bogner & P.C.Boyce, Passiflora quadriglandulosa Rodschied and Tectaria nayarii Mazumdar. Scindapsus lucens is likely to be native and previously overlooked, whereas Passiflora quadriglandulosa and Tectaria nayarii are exotic species which have escaped from cultivation and become naturalised. Another 10 species are rediscoveries of taxa previously considered to be nationally extinct:

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 and eight rediscoveries of species previously presumed nationally extinct are reported here along with national conservation assessments. The new records are Albertisia crassa Forman, Arcangelisia flava (L.) Merr., Chaetocarpus castanocarpus (Roxb.) Thwaites, Dendrokingstonia nervosa (Hook.f. & Thomson) Rauschert,

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.

Micrechites lancifolia (Hook.f.) D.J.Middleton & Livsh. is newly recorded for Singapore. A description and provisional conservation assessment are provided.

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.