Pl. Syst. Evol. 260: 83–85 (2006) DOI 10.1007/s00606-006-0438-5

Rosids - Reproductive structures, fossil and extant, and their bearing on deep relationships: Introduction

P. K. Endress1 and E. M. Friis2

1Institute of Systematic Botany, University of Zurich, Zurich, Switzerland 2Dept. of Palaeobotany, Swedish Museum of Natural History, Stockholm, Sweden

As a consequence of the rapid and successful developed on extant plants can also be used for progress of phylogenetics in the past decade, charcoalified fossil plants. These techniques there is an increasing imbalance between our allow not only anatomical and histological insight on phylogenetic relationships and the studies in fossils but also a morphological evolution of structure and biology of angio- reconstruction of the outer and inner surfaces sperms. However important a continuous of the organs in flowers (Scho¨nenberger improvement of resolution of the phylogenetic et al. 2001, Friis et al. 2003, Scho¨nenberger tree of angiosperms is, it remains of limited use 2005). if the structure and biology of the newly Rosids are one of the largest clades of the recognized clades are not studied concomi- flowering plants. Molecular systematics has tantly. identified a number of larger monophyletic In addition, despite the phylogenetic ad- components at the order level, some with the vances, the relationships between many large same circumscription as in traditional classifi- clades are still not well resolved. This is cations, others with new and unexpected asso- particularly true for the relationships between ciations of families or family clusters. Yet the the orders of rosids (Judd and Olmstead 2004, relationships between the orders, i.e. deep Soltis et al. 2005, Sytsma 2005). Thus straight- relationships, are not well resolved. Numerous forward comparative structural studies are fossil flowers, fruits and seeds recovered from hampered by such uncertainties. Nevertheless, Late Cretaceous floras over the past 25 years to avoid a vacuum we should not hesitate to are crucial for the recognition of deep rela- build on the available new fundament, even if tionships. Among Late Cretaceous rosids, taxa it is still shaky at some places. related to Saxifragales, Fagales, and Rosales In such comparative approaches the struc- are particularly common (e.g. Crane et al. ture of extant and fossil plants should be 2004, Crepet et al. 2004, Friis et al. 2005), but studied in an integrative way (Friis and Endress most of the enormous diversity of Late Creta- 1990, Endress and Friis 1994, Zimmer et al. ceous reproductive structures remains to be 2000, Scho¨nenberger et al. 2001, Doyle et al. studied. Based on our current knowledge it is 2003, Friis et al. 2006). Anatomical techniques clear that many extant lineages were well 84 P. K. Endress and E. M. Friis: Rosids - Reproductive structures, fossil and extant established in the Late Cretaceous floras co- structures. Hermsen et al. (2006) discuss the occurring with many extinct groups (e.g. Friis evolution of reproductive structures of Saxi- et al. 2006). Unusual structural features in fragales based on phylogenetic studies includ- flowers of larger clades may have shared ing fossil data. Von Balthazar et al. (2006) underlying patterns that are synapomorphies provide new aspects for floral development for these clades (e.g. the androecium in Mal- and evolution in extant Malvales, with a focus vales). However, such underlying patterns on the Malvatheca clade of Malvaceae s.l. often have not been worked out in detail and Matthews and Endress (2006) trace the distri- need critical comparative studies. Comparison bution of a new systematic feature in rosid of reproductive structures among extant flowers, specialized mucilage cells, and com- groups and fossils of rosids will also be an pare the characterization of new clades within important component in unravelling their four rosid orders by floral structural features. evolutionary history. Exceptional groups with Finally, Endress and Matthews (2006) make a rich fossil record but perhaps no direct extant first steps towards a floral structural charac- descendents need to be compared among terization of the new supraordinal clades of themselves and with the putative closest extant rosids as found recently in molecular phyloge- relatives (e.g. Normapolles pollen with floral netic studies by other authors. A symposium fossils and with extant Fagales). contribution by P. Herendeen who used the For the interpretation of fossil flowers fossil record of legumes to test evolutionary knowledge on the structure and biology of and biogeographic hypotheses is here not extant flowers is necessary. Vice versa, fossil included. flowers, if correctly interpreted, are not only We hope that this collection of publications crucial for calibration of evolutionary events, on structural features of rosids will catalyze as are fossils in general, but can reveal infor- new studies on the structural and evolutionary mation on the past diversity and evolution of understanding of rosids and their component extant reproductive structures. clades and also of other large angiosperm The following publications are essentially groups. the contributions to a Symposium on Rosids - Reproductive structures, fossil and extant, and their bearing on deep relationships, which was held at the XVII International Botanical Con- References gress, Vienna, in July 2005. The symposium von Balthazar M., Scho¨nenberger J., Alverson W. S., intended to include and, if possible, integrate Janka H., Bayer C., Baum D. A. (2006) Structure fossil and extant reproductive structures of and evolution of the androecium in the Malvat- rosids and to advance our knowledge on heca clade (Malvaceae s.l.) and implications for morphology and relationships and evolution Malvaceae and Malvales. Pl. Syst. Evol. 260: within larger clades of rosids. 171–197. Scho¨nenberger and von Balthazar (2006) Crane P. R., Herendeen P., Friis E. M. (2004) give an introduction and overview of the Fossils and plant phylogeny. Amer. J. Bot. 91: 1683–1699. current state of knowledge of extant and fossil Crepet W. L., Nixon K. C., Gandolfo M. A. (2004) rosid reproductive structures in the framework Fossil evidence and phylogeny: the age of major of phylogeny and evolution. Friis et al. (2006) angiosperm clades based on mesofossil and provide a review and new aspects on the macrofossil evidence from Cretaceous deposits. extinct Normapolles group (Fagales), which Amer. J. Bot. 91: 1666–1682. played an important role in the Late Creta- Doyle J. A., Eklund H., Herendeen P. S. (2003) ceous and Early Cainozoic flora and vegeta- Floral evolution in Chloranthaceae: implications tion of Europe, with special emphasis on the of a morphological phylogenetic analysis. Int. J. coordination of isolated pollen with floral Pl. Sci. 164 (5, Suppl.): S365–S382. P. K. Endress and E. M. Friis: Rosids - Reproductive structures, fossil and extant 85

Endress P. K., Friis E. M. (eds.) (1994) Early rosids, including a broad survey of floral muci- evolution of flowers. Pl. Syst. Evol. Suppl. 8: 1– lage cells. Pl. Syst. Evol. 260: 199–221. 229. Scho¨nenberger J. (2005) Rise from the ashes – Endress P. K., Matthews M. L. (2006) First steps reconstruction of charcoal fossil flowers. Trends towards a floral structural characterization of Pl. Sci. 10: 436–443. the major rosid subclades. Pl. Syst. Evol. 260: Scho¨nenberger J., von Balthazar M. (2006) Repro- 223–251. ductive structures and phylogenetic framework Friis E. M., Endress P. K. (1990) Origin and of the rosids – progress and prospects. Pl. Syst. evolution of angiosperm flowers. Adv. Bot. Res. Evol. 260: 87–106. 17: 99–162. Scho¨nenberger J., Friis E. M., Matthews M. L., Friis E. M., Pedersen K. R., Scho¨nenberger J. Endress P. K. (2001) Cunoniaceae in the Creta- (2003) Endressianthus, a new Normapolles- ceous of Europe: evidence from fossil flowers. producing plant genus of fagalean affinity from Ann. Bot. 88: 439–455. the Late Creataceous of Portugal. Int. J. Pl. Sci. Soltis D. E., Soltis P. S., Endress P. K., Chase M. W. 164 (Supplement), S201–S223. (2005) Phylogeny and evolution of angiosperms. Friis E. M., Pedersen K. R., Crane P. R. (2005) Sinauer, Sunderland, MA. When Earth started blooming: insights from the Sytsma K. J., Hall J. (2005) Rosid angiosperms: fossil record. Curr. Opin. Pl. Biol. 8: 5–12. circumscription, issues, and systematic advances. Friis E. M., Pedersen K. R., Crane P. R. (2006) XVII International Botanical Congress, Vienna. Cretaceous angiosperm flowers: innovation and Abstract 5.8.3., pp. 84–85. evolution in plant reproduction. Palaeogeogr., Zimmer E. A., Qiu Y.-L., Endress P. K., Friis E. M. Palaeoclimatol., Palaeoecol. 232: 251–293. (eds.) (2000) Current perspectives on basal Friis E. M., Pedersen K. R., Scho¨nenberger J. angiosperms. Int. J. Pl. Sci. 161 (Suppl. 6): S1– (2006) Normapolles plants: a prominent compo- S248. nent of the Cretaceous rosid diversification. Pl. Syst. Evol. 260: 107–140. Hermsen E. J., Nixon K. C., Crepet W. L. (2006) Addresses of the authors: Peter K. Endress Fossil reproductive structures of Saxifragales (e-mail: [email protected]), Institute of and saxifrage evolution. Pl. Syst. Evol. 260: 141– Systematic Botany, University of Zurich, Zolliker- 169. strasse 107, 8008 Zurich, Switzerland. Else Marie Judd W. S., Olmstead R. G. (2004) A survey of Friis, Dept. of Palaeobotany, Swedish Museum of tricolpate (eudicot) phylogenetic relationships. Natural History, Box 50007, 104 05 Stockholm, Amer. J. Bot. 91: 1627–1644. Sweden. Matthews M. L., Endress P. K. (2006) Floral structure and systematics in four orders of