In systematics, patterns of derived characters shared by two or more organisms are used for hypotheses of common ancestry. Characters in this sense are differences in morphology, anatomy, embryology, or chemistry, and may even be differences in DNA or RNA sequences.
Nucleotide sequence data from investigations of plant genomes are normally deposited in a genebank from which they can be obtained by the scientific community. At the Swedish Museum of Natural History, research in this field is carried out at the Laboratory for Molecular Systematics.
By using computers for cladistic analysis, nested sets of characters indicate phylogenetic relationships between species, genera, or higher taxonomic ranks. The hypotheses can be illustrated as so called cladograms, hierarchical tree-like diagrams where organisms with a common origin diagnosed by nested sets of derived characters form monophyletic groups.
At the Department of Phanerogamic Botany, systematic research is mainly focused on the following plant groups:
The family Asclepiadaceae (Jens Klackenberg)
The project is focused on the phylogenetic interrelationships in the tribe Secamoneae. Taxonomic revisions of several genera of the tribe have been published, and others will follow. Within this project, a number of new species and genera have been discovered and described from Madagascar. The work is mainly based on morphological data but the results will eventually be compared with DNA sequence data. The molecular work is conducted by Laure Civeyrel, Montpellier.
The family Asteraceae (Bertil Nordenstam)
In the tribe Senecioneae there are ongoing revisions of generic and species delimitation in several genera from South Africa (Othonna, Euryops), the West Indies and South America (Senecio, Aequatorium and new genera), the Canary Islands (Senecio), and Scandinavia (Tephroseris, Senecio). The tribe has been reviewed for the "Families and Genera of Vascular Plants" project and 138 genera are recognized, some still undescribed. Treatments for regional floras such as the Flora of Ecuador are underway.
The predominantly South African tribe Calenduleae is being studied in some detail on genus/species level. A preliminary study was made in collaboration with Ida Trift of the University of Stockholm, based on morphological and molecular data. An extended study including much more material is going on in cooperation with Alan Wood, Stellenbosch, South Africa. The tribe was treated for the FGVP project on the basis of current knowledge (in press). A revision of Syncarpha of the tribe Gnaphalieae is also well underway.
Colchicaceae (Bertil Nordenstam)
The Colchicaceae has been revised and published in Kubitzki's "The Families and Genera of Vascular Plants", but a number of revisions still remain to be performed at the species level, e.g. in the genus Wurmbea in South Africa and in Australia-New Zealand.
The order Ericales (Arne A. Anderberg)
Sapotaceae (Ulf Swenson)
Sapotaceae are a pantropical plant family with approximately 1250 described species in 53 genera. The family is particularly rich in species in South America and Australasia. The research aims to investigate the phylogeny and historical biogeography of a pantropical group present in former areas of Gondwana. There is a discrepancy between present distribution and the break-up of Gondwana. For instance, how can a plant family be pantropical if it originated after the break-up of Gondwana? Questions, answers, and evidence of vicariance, long-distance dispersal, and establishment are therefore pertinent. However, in Australasia, especially New Caledonia, present knowledge of the family is particularly poor. Generic and specific delimitations need to be revised as well as many species (and genera) need to be described. The preliminary aims to investigate the origin and biogeography are hampered by this poor knowledge. Nevertheless, this international research make use of both morphological and molecular data. Apart from the scientific publications the work generates, the aim is to produce a revised monograph of Sapotaceae in New Caledonia, an area where the natural vegetation continuously is nibbled by fires, mining projects, and logging.