Rosids

Rosids
Euphorbia heterophylla
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Rosids
Orders
See text

The rosids are members of a large clade of flowering plants, containing about 70,000 species,^[1] more than a quarter of all angiosperms.^[2] The clade is divided into 16 to 20 orders, depending upon circumscription and classification. These orders, in turn, together comprise about 140 families.^[3] The rosids and the asterids are by far the largest clades in the eudicots.

Fossil rosids are known from the Cretaceous period. Molecular clock estimates indicate that the rosids originated in the Aptian or Albian stages of the Cretaceous, between 125 and 99.6 million years ago.^[4][5]

The name

The name "rosids" is based upon the name "Rosidae", which had usually been understood to be a subclass. In 1967, Armen Takhtajan showed that the correct basis for the name "Rosidae" is a description of a group of plants published in 1830 by Friedrich Gottlieb Bartling.^[6] This clade was later renamed "Rosidae" and has been variously delimited by different authors. The name "rosids" is informal, and not assumed to have any particular taxonomic rank like the names authorized by the ICBN. The rosids are monophyletic based upon evidence found by molecular phylogenetic analysis.

Three different definitions of the rosids are currently in use. Some authors include the orders Saxifragales and Vitales in the rosids.^[7] Others exclude both of these orders.^[8] The circumscription used in this article is that of the APG II classification, which includes Vitales, but excludes Saxifragales.

Relationships

The rosids and Saxifragales form a clade.^[1][8] This is one of 6 groups that compose the Pentapetalae (core eudicots minus Gunnerales),^[9] the others being Berberidopsidales, Caryophyllales, Dilleniales, Santalales, and the asterids. Almost nothing is known about the relationships between these groups.

Classification

The rosids consist of two groups: the order Vitales and the eurosids (true rosids). The eurosids, in turn are divided into seven groups: Fabidae, Geraniales, Myrtales, Crossosomatales, Picramniales,^[8] Malvidae,^[9] and the unplaced family Apodanthaceae.^[10] The Fabidae are often called the fabids, or eurosids I. Likewise, the Malvidae are often called the malvids, or eurosids II.

Orders

The rosids consist of 17 orders and 2 families that are placed incertae sedis (not in any order). In addition to Vitales, Geraniales, Myrtales, Crossosomatales, and Picramniales, there are 8 orders in Fabidae and 4 orders in Malvidae. In 2009, Hengchang Wang and co-authors proposed that Malvidae be expanded to include Geraniales, Myrtales, Crossosomatales, and Picramniales. This larger circumscription of Malvidae received strong statistical support (100% bootstrap percentage) in their analysis. Some of the orders have only recently been recognized.^[8] These are Vitales,^[11] Zygophyllales,^[12] Crossosomatales,^[13] Picramniales,^[14] and Huerteales.^[15]

Unplaced families

The families Apodanthaceae and Huaceae are included in the rosids, but not placed in any of its orders.

Apodanthaceae is an enigmatic family of achlorophyllous parasites. They have been provisionally placed in Cucurbitales by some,^[8] but their affinities remain obscure.^[10] The chloroplast genes that have been used to infer plant phylogeny do not provide much phylogenetic information for plants that lack chlorophyll, because in this case, these genes are nonfunctional pseudogenes.

The family Huaceae is a member of the COM (Celastrales, Oxalidales, Malpighiales) clade of Fabidae. The question about Huaceae is whether it should be included in one of the COM orders or in an order by itself as a 4th member of the COM clade. Two studies have indicated that it should be placed in Oxalidales,^[16][17] while one has indicated that it should not.^[1]

Phylogeny

The phylogeny shown below is adapted from Wang and co-authors (2009),^[1] with order names from the Angiosperm Phylogeny Website.^[8] Branches with less than 50% bootstrap support are collapsed. Other branches have 100% bootstrap support except where shown.

	Vitales
eurosids	Fabidae  Zygophyllales COM clade  Celastrales Oxalidales Malpighiales nitrogen‑fixing clade  Fabales Rosales Fagales Cucurbitales Malvidae sensu lato  65%  Geraniales Myrtales Crossosomatales Picramniales Malvidae sensu stricto  Sapindales Huerteales Brassicales Malvales

The nitrogen-fixing clade contains a high number of actinorhizal plants (which have root nodules containing nitrogen fixing bacteria, helping the plant grow in poor soils). Not all plants in this clade are actinorhizal, however.

References

1. ^ ^{a b c d} Hengchang Wang, Michael J. Moore, Pamela S. Soltis, Charles D. Bell, Samuel F. Brockington, Roolse Alexandre, Charles C. Davis, Maribeth Latvis, Steven R. Manchester, and Douglas E. Soltis (10Mar2009), "Rosid radiation and the rapid rise of angiosperm-dominated forests", Proceedings of the National Academy of Sciences 106 (10): 3853–3858, doi:10.1073/pnas.0813376106, PMC 2644257, PMID 19223592, http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2644257 
2. ^ Robert W. Scotland and Alexandra H. Wortley (2003), "How many species of seed plants are there?", Taxon 52 (1): 101–104, doi:10.2307/3647306, JSTOR 3647306 
3. ^ Douglas E. Soltis, Pamela S. Soltis, Peter K. Endress, and Mark W. Chase (2005), Phylogeny and Evolution of the Angiosperms, Sunderland, MA, USA: Sinauer, ISBN 978-0878938179 
4. ^ Davies, T.J., Barraclough, T.G., Chase, M.W., Soltis, P.S., Soltis, D.E., and Savolainen, V. (2004), "Darwin's abominable mystery: Insights from a supertree of the angiosperms", Proceedings of the National Academy of Sciences 101 (7): 1904–1909, Bibcode 2004PNAS..101.1904D, doi:10.1073/pnas.0308127100, PMC 357025, PMID 14766971, http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=357025 
5. ^ Susana Magallón and Amanda Castillo (2009), "Angiosperm diversification through time", American Journal of Botany 96 (1): 349–365, doi:10.3732/ajb.0800060, PMID 21628193 
6. ^ James L. Reveal (2008 onward), "A Checklist of Family and Suprafamilial Names for Extant Vascular Plants", Home page of James L. Reveal and C. Rose Broome, http://www.plantsystematics.org/reveal/pbio/fam/supgennames.html 
7. ^ J. Gordon Burleigh, Khidir W. Hilu, and Douglas E. Soltis (2009), File 7, "Inferring phylogenies with incomplete data sets: a 5-gene, 567-taxon analysis of angiosperms", BMC Evolutionary Biology 9: 61, doi:10.1186/1471-2148-9-61, PMC 2674047, PMID 19292928, http://www.biomedcentral.com/content/supplementary/1471-2148-9-61-S7.pdf 
8. ^ ^{a b c d e f} Peter F. Stevens (2001 onwards), Angiosperm Phylogeny Website, http://www.mobot.org/MOBOT/Research/APweb/welcome.html 
9. ^ ^{a b} Philip D. Cantino, James A. Doyle, Sean W. Graham, Walter S. Judd, Richard G. Olmstead, Douglas E. Soltis, Pamela S. Soltis, and Michael J. Donoghue (2007), "Towards a phylogenetic nomenclature of Tracheophyta", Taxon 56 (3): 822–846, doi:10.2307/25065865, http://www.phylodiversity.net/donoghue/publications/MJD_papers/2007/164_Cantino_Taxon07.pdf 
10. ^ ^{a b} Daniel L. Nickrent, "Apodanthaceae", The Parasitic Plant Connection, http://www.parasiticplants.siu.edu/Apodanthaceae/index.html 
11. ^ James L. Reveal. (1995). page 72 in Newly required suprageneric names in vascular plants. Phytologia 79(2):68-76
12. ^ Chalk, L. 1983. Wood structure. Pp. 1-51 [1-2 by C. R. Melcalfe], in Metcalfe, C. R., & Chalk, L., Anatomy of the Dicotyledons, Second Edition. Volume II. Wood Structure and Conclusion of the General Introduction. Clarendon Press, Oxford. ISBN 978-0198545590.
13. ^ Klaus Kubitzki (2007), "Introduction to Crossosomatales", in Klaus Kubitzki, The Families and Genera of Vascular Plants, vol.IX, Berlin,Heidelberg: Springer-Verlag 
14. ^ John Hutchinson The Families of Flowering Plants 3rd edition. 1973. Oxford University Press.
15. ^ Andreas Worberg, Mac H. Alford, Dietmar Quandt, and Thomas Borsch (2009), "Huerteales sister to Brassicales plus Malvales, and newly circumscribed to include Dipentodon, Gerrardina, Huertea, Perrottetia, and Tapiscia", Taxon 58 (2): 468–478 
16. ^ Douglas E. Soltis, Matthew A. Gitzendanner, and Pamela S. Soltis (2007), "A 567-taxon data set for angiosperms: The challenges posed by Bayesian analyses of large data sets", International Journal of Plant Sciences 168 (2): 137–157, doi:10.1086/509788 
17. ^ Li-Bing Zhang and Mark P. Simmons (2006), "Phylogeny and delimitation of the Celastrales inferred from nuclear and plastid genes", Systematic Botany 31 (1): 122–137, doi:10.1600/036364406775971778