“Big” plant genera, those of 500 or more species, have not only occasioned interest among systematic botanists, but for geographical, ecological or horticultural reasons, have also become well­established popular concepts. Their size has rendered them difficult, if not impossible, to study in their entirety; there have been few full revisions since the nineteenth century. Despite their embodiment of significant taxonomic, biological and evolutionary questions, from the 1980s their importance has been more generally recognised, and recent technological and methodological developments have made it easier to come to grips with their study. This paper synthesizes growth impediments to our knowledge of these genera and possible approaches to studying them. Of the 57 genera currently thought to have 500 or more species, 22 of these were also considered in 1883 to be large (300 or more species). Others gained their prominence as a result of later exploration, some of it driven by enthusiasts. It is argued that comparisons of size, phenomena, and processes will only be possible by comprehensive study of the lineages comprising these genera and their immediate historical relatives; uncritical lists or relatively limited samples are not enough. Such studies will be of great scientific as well as cultural benefit.

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With its large proportion of endemic taxa, complex geological past, and location at the confluence of the highly diverse Malesian and Australian floristic regions, Papuasia-the floristic region comprising the Bismarck Archipelago, New Guinea, and the Solomon Islands-represents an ideal natural experiment in plant biogeography. However, scattered knowledge of its flora and limited representation in herbaria have hindered our understanding of the drivers of its diversity. Focusing on the woody angiosperm genus Schefflera (Araliaceae), we ask whether its morphologically defined infrageneric groupings are monophyletic, when these lineages diverged, and where (within Papuasia or elsewhere) they diversified. To address these questions, we use a high-throughput sequencing approach (Hyb-Seq) which combines target capture (with an angiosperm-wide bait kit targeting 353 single-copy nuclear loci) and genome shotgun sequencing (which allows retrieval of regions in high-copy number, e.g., organellar DNA) of historical herbarium collections. To reconstruct the evolutionary history of the genus we reconstruct molecular phylogenies with Bayesian inference, maximum likelihood, and pseudo-coalescent approaches, and co-estimate divergence times and ancestral areas in a Bayesian framework. We find strong support for most infrageneric morphological groupings, as currently circumscribed, and we show the efficacy of the Angiosperms-353 probe kit in resolving both deep and shallow phylogenetic relationships. We infer a sequence of colonization to explain the present-day distribution of Schefflera in Papuasia: from the Sunda Shelf, Schefflera arrived to the Woodlark plate (presentday eastern New Guinea) in the late Oligocene (when most of New Guinea was submerged) and, subsequently (throughout the Miocene), it migrated westwards (to the Maoke and Bird's Head Plates and thereon) and further diversified, in agreement with previous reconstructions.

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