Rhamnus & Frangula

I have used  Frangula alnus (Rhamnaceae) as a field system, mainly for studying reproductive phenology. To get a wider picture of trait evolution in the Rhamnus-Frangula clade, we are pursuing some comparative studies based on published and developing phylogenetic hypotheses (Bolmgren & Oxelman (2004);  ongoing collaboration with Ryan Stewart, Torsten Eriksson, and Magnus Lundberg).
 
Rhamnus s.l. L. (Rhamnaceae) comprise insect-pollinated and bird-disseminated dwarf-shrubs, shrubs, or trees, mainly inhabiting temperate to subtropical areas of the Northern hemisphere. A few species within Rhamnus s.str. are found in Africa, with R. prionoides reaching as far as South Africa, whereas the Frangula group has an area of diversification in the montane areas of the Neotropics with its southern limit in Chile and Argentina.
 
Richardson et al. (2000) suggested that Rhamnus s.l. belong to a well supported tribe within Rhamnaceae characterized by drupaceous fruits. This tribe also includes Berchemia, Reynosia, Condalia, Karwinskia, Rhamnidium, Krugiodendron, Rhamnella, Sageretia, and Scutia. As with all other species within Rhamnaceae, the flowers of the Rhamnus s.l. clade are characterized by stamens positioned opposite to the petals, but a large number of species within Rhamnus s.str., e.g., R. cathartica and R. crocea, have 4-merous flowers, differing from the general 5-merous floral pattern within Rhamnaceae.
 
In Bolmgren & Oxelman (2004) we tested the monophyly of the previously proposed genera Alaternus, Frangula, Oreoherzogia, and Rhamnus s.str. within the Rhamnus s.l. clade. So far, only Rhamnus has gained general acknowledgement (e.g. Medan & Schirarend 2004). Based on a global sample of 22 species, a phylogenetic hypotheses was derived using parsimony analysis of variation in trnL-F (chloroplast) and ITS (nuclear) DNA regions. Both Alaternus, Frangula, and Oreoherzogia gained strong support, but as the resolution between Alaternus, Oreoherzogia, and the rest of Rhamnus s.str. was less clear it was considered unjustified to split the rest of Rhamnus into smaller genera. Thus, the study could only support the recognition of Frangula and the rest of Rhamnus as monophyletic sister genera. The ongoing collaboration with Ryan Stewart, Torsten Eriksson, and Magnus Lundberg approaches some of the pending issues from the Taxon study.


Kjell Bolmgren
PhD
  
E-mail:
kjell.bolmgren/at/esf.slu.se
 
 
Postal and Visiting Address:
Swedish University of Agricultural Sciences
c/o Department of Botany
Stockholm University
SE-106 91 Stockholm
SWEDEN
 
 
Telephone:
(INT + 46)-730-670365
(INT + 46)-8-164899