Documenting and Analysing Patterns in the Diversity and Distribution of Flowering Plant Genera
Distributions of all vascular plant genera have been compiled from herbarium specimens at RBG Kew, and these data are maintained as part of the Vascular Plant Families and Genera database. The database consists of more than 14,000 genera, of which more than 97% are represented in the RBG Kew herbarium, with more than 70,000 distribution records at a regional level (TDWG Level 2). An extensive although not exhaustive literature search has also been undertaken, although verified herbarium specimens still account for more than 96% of records, and, in general, herbarium collections were found to supplement literature records and not vice versa. As well as itself being a very valuable curatorial resource, this database has also been analysed for large-scale patterns in the diversity and distribution of flowering plants.
For example, a strong latitudinal gradient in diversity is apparent at family, genus and species levels, though while western South America is most diverse at species and genus levels, it is the SW Pacific which is most diverse at family level. However, the number of families and genera per region is very strongly correlated overall, irrespective of the region. There is a very strong relationship between both family and genus diversity and area, though not for numbers of endemic genera. For both families and genera, the range-size frequency distribution is highly skewed towards small range sizes (more so for genera than for families), which account for the majority of diversity.
Analysing floristic similarity between different regions of the world reveals very strongly supported continental groups, since most genera are confined to particular continents, although the latitudinal difference between regions is a better predictor of floristic similarity than is simply distance between regions. Distribution patterns show strong regional clustering, with almost 40% of genera single-region endemics, and approximately 20% of world distribution patterns accounting for about 80% of total angiosperm genus diversity. Analysis of distribution patterns reveals a strong correlation between diversity and number of floristic elements, which intersect to form the diversity of a region. Since only a minority of genera are endemic to any one region, the complexity of these floristic elements forms an important component of the diversity within that region.
The principal output of this project has so far been a PhD thesis, submitted in 2004 by and awarded in 2005 to Neil Brummitt. A series of papers based on this work has also been appearing, or is in press or in preparation. Maintenance of this database is also a continuing aspect of a core-funded post [NAB], as is the development of further analyses and the linking of this work to similar emerging projects utilising other comparable datasets at RBG Kew, for example IPNI or the World Checklists and Bibliographies series.