When I studied the leguminous plants I was told about a Superfamily which included all the groups with this kind of fruit, the legume. I was told that Mimosaceae, Cesalpiniaceae and Fabaceae were three different families with this common trait, the legume. The main difference between them was the flower: Mimosaceae was supposed to be the most primitive group because its flower and the Fabaceae the most derived one. Now I see this scenario is not supported by molecular studies and APG classification system considers a unique family called Fabaceae. "Cesalpiniaceae" is now considered a paraphyletic group, although in the phylogenetic tree of this new unique family "Fabaceae" you can find that Faboideae and Mimosoideae are true monophyletic groups of species. Could anybody explain or put a reference about how the flower of this family has evolved? Thank you.
I can't explain too much about flower evolution. But it's very possible that the traditional concept of "Caesalpiniaceae" won`t exist any more.
It's well established that Faboideae and Mimosoideae are monophylletic.
The Fabaceae started their diversification approximately 60 million years ago and the most important clades separated some 50 million years ago (Lavin, 2005). A rapid family wide diversification happened between 59 and 34 million years ago. Also, we must consider that nucleotide substitution rate is different among different groups. And it's difficult to asign the fossil records to every group (extant lineages too). Therefore, it doesn't seems to be clear the idea of Mimosaceae was supposed to be the most primitive group. I think we need further studies about this.
Take a look at this paper:
LAVIN, et al. 2004. Evolutionary Rates Analysis of Leguminosae Implicates a Rapid Diversification of Lineages during the Tertiary. Systematic Biology 54 (4): 530-549.
Quite interesting question. I hope some expert will help us with this !!.
Regards.
http://sysbio.oxfordjournals.org/content/54/4/575.full
If you ever got any questions in this respect, go to Peter F. Stevens' APweb at MoBot, it's the most up-to-date and authoritative source about anything regarding angiosperm phylogeny, evolution, morphology etc.
http://www.mobot.org/MOBOT/research/APweb/
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