Biol317 Phylogeny and Classification Example Exercise Fabaceae & Rosaceae Infra-Familial Classification

BIOL317 PHYLOGENY AND CLASSIFICATION EXAMPLE EXERCISE FABACEAE & ROSACEAE INFRA-FAMILIAL CLASSIFICATION ANSWER KEY Q 1A. Faboideae and Mimosoideae are monophyletic. Caesalpinioideae is paraphyletic. Q 1B. Probably the caesalpinioid flower with weak bilateral symmetry, showy, unfused petals, and 10 free stamens. Since the clades corresponding with Faboideae and Mimosoideae are derived within a grade of Caesalpinioideae species, it seems likely that the flag flower and brush flower are each derived from a caesalpinioid ancestral form. Q 1C. It is clear that revision is needed because Caesalpinioideae is paraphyletic, and we want to avoid having taxa that are not monophyletic. However, it is not clear what the best solution would be. We could avoid naming any subfamilies, which would solve the problem of the paraphyletic Caesalpinioideae. However, we would then have over 18,000 species lumped into one higher-order group, which (arguably) does not provide us with an adequate system to describe and communicate about them. Alternatively, we could break up the Caesalpinioideae into several, smaller groups, corresponding with the monophyletic lineages depicted in the phylogenetic tree. This approach has its drawbacks, too: we must find ways to define these smaller groups morphologically, since they more-or-less share a common, ancestral floral form. Caesalpinioideae is widely recognized to be paraphyletic as traditionally circumscribed, but phylogenetic relationships within Fabaceae are an area of active research, and formal revisions at the rank of subfamily have not yet been made. For more information and an up-to-date discussion on the topic, see: The Legume Phylogeny Working Group. 2013. Legume phylogeny and classification in the 21st century: progress, prospects, and lessons for other species-rich clades. Taxon 62: 217-248 (available at http://loco.biosci.arizona.edu/PDF/LPWG.2013.pdf). Of particular relevance is the discussion under “Where are we along the road to a family-wide phylogenetic classification?” on p. 236. Q 2A. Rosoideae, Amygdaloideae, and Maloideae are monophyletic in this tree. Spiraeoideae is paraphyletic. Q 2B. This is tricky. The common ancestor of all species of Rosaceae gave rise to two daughter lineages: one leading to Rosoideae, and the other leading to a clade comprising the other subfamilies. So, it isn’t clear whether the ancestral fruit type is best represented by that of the present-day members of Rosoideae, or of the Spiraeoideae (which clearly seems to be ancestral relative to Amygdaloideae and Maloideae). We can infer that fruit traits shared between Rosoideae and Spiraeoideae might have been ancestral, ie. multiple, free simple pistils, but we can’t easily say whether fruits were fleshy or dry, many or single- seeded, aggregate or not, etc. Q 2C. In this simplified tree, Spiraeoideae is non-monophyletic, so taxonomic revision is needed. As outlined above (answer to Q1 C), we might decide not to recognize any subfamilies, which would solve the problem, but leave us with a rather unsatisfactory classification scheme, given the size and diversity of Rosaceae. We might split the Spiraeoideae into several, smaller subfamilies, corresponding with monophyletic lineages as shown in the phylogenetic tree. Again, this would solve the problem, but create the new problem of how to define the new subfamilies morphologically. In Rosaceae, we can see a third, relatively simple solution: since the family consists of two large, monophyletic clades, we could recircumscribe subfamilies to correspond to these clades, ie. transfer all the species of Maloideae and Amygdaloideae into Spiraeoideae. That is essentially what taxonomists have done. Most of the species of Rosaceae are now classified in two subfamilies: Rosoideae and Amygdaloideae (since Amygdaloideae is the older name - in use before either Spiraeoideae or Maloideae - it takes precedence for the name assigned to the new, expanded group). In reality, the Rosaceae phylogeny and subfamilial classification is not quite this simple; a few species have been omitted from this example exercise. For more information, see: Potter D, Eriksson T, Evans RC, Oh S, Smedmark JEE, Morgan DR, Kerr M, Robertson KR, Arsenault M, Dickinson TA, Campbell CS. 2007. Phylogeny and classification of Rosaceae. Plant Systematics and Evolution 266: 5-43 (available at http://biology.umaine.edu/Amelanchier/Rosaceae_2007.pdf). Note that the authors use Spiraeoideae as the name for the combined subfamily, but the ultimate decision (at the International Botanical Congress 2011) was that Amygdaloideae is the correct name for this group. Systematics is a complicated endeavor! Robert Frost expressed his confusion with taxonomy (and admiration for a certain, unnamed, someone) in the poem “The Rose Family”: The rose is a rose, And was always a rose. But the theory now goes That the apple's a rose, And the pear is, and so's The plum, I suppose. The dear only knows What will next prove a rose. You, of course, are a rose - But were always a rose. .

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