Zurich Open Repository and Archive University of Zurich Main Library Strickhofstrasse 39 CH-8057 Zurich www.zora.uzh.ch Year: 2006 First steps towards a floral structural characterization of the major rosid subclades Endress, P K ; Matthews, M L Abstract: A survey of our own comparative studies on several larger clades of rosids and over 1400 original publications on rosid flowers shows that floral structural features support to various degrees the supraordinal relationships in rosids proposed by molecular phylogenetic studies. However, as many apparent relationships are not yet well resolved, the structural support also remains tentative. Some of the features that turned out to be of interest in the present study had not previously been considered in earlier supraordinal studies. The strongest floral structural support is for malvids (Brassicales, Malvales, Sapindales), which reflects the strong support of phylogenetic analyses. Somewhat less structurally supported are the COM (Celastrales, Oxalidales, Malpighiales) and the nitrogen-fixing (Cucurbitales, Fagales, Fabales, Rosales) clades of fabids, which are both also only weakly supported in phylogenetic analyses. The sister pairs, Cucurbitales plus Fagales, and Malvales plus Sapindales, are structurally only weakly supported, and for the entire fabids there is no clear support by the present floral structural data. However, an additional grouping, the COM clade plus malvids, shares some interesting features but does not appear as a clade in phylogenetic analyses. Thus it appears that the deepest split within eurosids- that between fabids and malvids - in molecular phylogenetic analyses (however weakly supported) is not matched by the present structural data. Features of ovules including thickness of integuments, thickness of nucellus, and degree of ovular curvature, appear to be especially interesting for higher level relationships and should be further explored. Although features of interest are not necessarily stable at the level of a large clade, they do show a considerable concentration in particular clades and are rare or lacking in others. This may be viewed as a special trend for this feature to evolve in this group or to be conserved as a synapomorphy (or a combination of both) DOI: https://doi.org/10.1007/s00606-006-0444-7 Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-155761 Journal Article Published Version Originally published at: Endress, P K; Matthews, M L (2006). First steps towards a floral structural characterization of the major rosid subclades. Plant Systematics and Evolution, 260(2-4):223-251. DOI: https://doi.org/10.1007/s00606-006-0444-7 Pl. Syst. Evol. 260: 223–251 (2006) DOI 10.1007/s00606-006-0444-7 First steps towards a floral structural characterization of the major rosid subclades P. K. Endress and M. L. Matthews Institute of Systematic Botany, University of Zurich, Switzerland Received November 3, 2005; accepted January 23, 2006 Published online: July 20, 2006 Ó Springer-Verlag 2006 Abstract. A survey of our own comparative studies integuments, thickness of nucellus, and degree of on several larger clades of rosids and over 1400 ovular curvature, appear to be especially interesting original publications on rosid flowers shows that for higher level relationships and should be further floral structural features support to various degrees explored. Although features of interest are not the supraordinal relationships in rosids proposed necessarily stable at the level of a large clade, they by molecular phylogenetic studies. However, as do show a considerable concentration in particular many apparent relationships are not yet well clades and are rare or lacking in others. This may resolved, the structural support also remains ten- be viewed as a special trend for this feature to tative. Some of the features that turned out to be of evolve in this group or to be conserved as a interest in the present study had not previously synapomorphy (or a combination of both). been considered in earlier supraordinal studies. The strongest floral structural support is for malvids Key words: Rosids, eurosids, fabids, malvids, (Brassicales, Malvales, Sapindales), which reflects nitrogen-fixing clade, supraordinal relationships, the strong support of phylogenetic analyses. Some- floral structure, ovules. what less structurally supported are the COM (Celastrales, Oxalidales, Malpighiales) and the nitrogen-fixing (Cucurbitales, Fagales, Fabales, Introduction Rosales) clades of fabids, which are both also only weakly supported in phylogenetic analyses. The In the past decade new results of molecular sister pairs, Cucurbitales plus Fagales, and Malva- phylogenetic studies have brought tremendous les plus Sapindales, are structurally only weakly progress in our perception of plant relation- supported, and for the entire fabids there is no clear ships at all hierarchical levels. In the frame- support by the present floral structural data. work of the eudicots, which were established in However, an additional grouping, the COM clade morphological cladistic studies (Donoghue plus malvids, shares some interesting features but and Doyle 1989, Doyle and Hotton 1991) does not appear as a clade in phylogenetic analyses. Thus it appears that the deepest split within slightly before the onset of the ground eurosids–that between fabids and malvids - in breaking molecular works, orders were newly molecular phylogenetic analyses (however weakly circumscribed, and some quite substantially. supported) is not matched by the present structural Also there are new assemblages of orders that data. Features of ovules including thickness of constitute formerly unrecognized large clades 224 P. K. Endress and M. L. Matthews: Floral structure of rosid subclades (outlined in APG 2003, Soltis et al. 2005). The two subclusters, which receive weaker support: content of the rosids (in the premolecular era the ‘‘nitrogen-fixing clade’’ (Cucurbitales, Fa- called Rosidae, Rosiflorae, or Rosanae, Dahl- gales, Fabales, Rosales) and the ‘‘COM’’ clade gren 1980, Cronquist 1981, Takhtajan 1987, (Celastrales, Oxalidales, and Malpighiales). Thorne 1992) has considerably changed. Within the ‘‘nitrogen-fixing clade’’, Cucurbi- In great contrast to the progress in molec- tales and Fagales appear as sisters. A small ular phylogenetic research, understanding of order, Zygophyllales (Zygophyllaceae and structural features, not only for these newly Krameriaceae) appears as sister to fabids in circumscribed large clades but also for lower some analyses but with less than 50% support levels, orders, families, and genera, has not (Soltis et al. 2005); therefore we leave it in an advanced to the same degree. New structural unresolved position in rosids in our figures. characters must be explored that have not been Within malvids, Malvales and Sapindales discussed before in macrosystematic studies, appear as sisters, both with weak support and likewise characters that were earlier used (APG 2003, Soltis et al. 2005). The difficulties should be probed for new large clades. that have been encountered when trying to Rosids are a very large clade including resolve the phylogenetic topology at various about 30% of all angiosperm species. The levels may have been caused by the probable clade contains 14 mainly large orders, most of rapid early diversification of rosids and some which are well supported by molecular phylo- of their subclades in the Cretaceous (e.g. Davis genetic studies (Soltis et al. 2000, 2005; APG et al. 2005, Soltis et al. 2005), and perhaps, in 2003; Judd and Olmstead 2004; Scho¨ nenberger addition, because of the large size of these and von Balthazar 2006). However, it is clades, which may need more extensive sam- unclear for most of these orders how they are pling. related to each other (Fig. 1). Thus, despite These apparent largest subclades of the impressive progress in some respects, the rosids are new and have never been considered process of phylogenetic elucidation is only at as clades before. Their sheer size makes their its beginning. structural characterization a massive task, and Two major clusters of orders appear in fact, a structural characterization has not moderately to well supported as clades in yet been performed (see also Stevens 2001 molecular studies: fabids (=eurosids I), and onwards). malvids (=eurosids II). Within fabids there are This study is an attempt to make a first step towards this goal. We concentrate on the highest levels within rosids: assemblages of orders (but also this at different levels), while considering all current orders for data collec- tion, including Saxifragales and Vitaceae as potential sister groups of rosids. Our study is based on two sources: (1) the studies on several orders of rosids that we carried out over the past five years (Matthews et al. 2001; Scho¨ - nenberger et al. 2001; Matthews and Endress 2002, 2004, 2005a, b, 2006, Endress 2005; Endress and Matthews 2006) plus our earlier studies in other rosids and putative sister Fig. 1. Cladogram of rosids plus potential sisters groups (Endress 1967, 1977, 1989; Endress et (Saxifragales and Vitaceae) (modified after APG 2003 al. 1983; Hufford and Endress 1989; Endress and Soltis et al. 2005, with jackknife values from and Stumpf 1990, 1991; Sutter and Endress Soltis et al. 2005) 1995; Merino Sutter and Endress 2003; Blarer P. K. Endress and M. L. Matthews: Floral structure of rosid subclades 225 et al. 2004; Merino Sutter et al. 2006) and (2) a following