Brigitte Marazzi

Postdoctoral researcher

Department of Ecology and Evolutionary Biology

University of Arizona

1041 E Lowell Street

Tucson, AZ 85721

Tel. (001)520-626-7860

Office BSE 125

bmarazzi at email.arizona.edu

RESEARCH INTERESTS

My research interests cover topics in botany and macroevolution, addressing questions like: How did morphological diversity of extant plants evolve? How is it characterized? Did species traits such as morphological novelties have influenced lineage diversification? This means to ultimately increase our understanding of why some taxonomic groups are remarkably more diverse than related groups, which is one of the central questions in evolutionary biology.

Specifically, my current research focuses on the large, widespread, and diverse genus Senna (Leguminosae, Caesalpinioideae, Cassiinae) to explore the evolution of plant morphological novelties and key innovations. I am also highly interested in character specialization and character complexes, especially at the floral morphological level.

Senna: An Ideal Study Organism

Senna Miller (formerly included in Cassia L.) is characterized by the presence of extrafloral nectaries in numerous species and a distinctive floral morphology, it displays a high diversity of habits (Fig. 1), and has successfully colonized a wide range of habitats in different climates and latitudes. Of the 300-350 species currently ascribed to the genus, 80% occur in the Americas [1]. Since long time, some species are used for their medicinal properties (especially as a purge) and are appreciated as ornamentals, owing to their showy yellow flowers [2, 3]. Due to the lack of a treatment of the genus worldwide, the ‘big picture’ of Senna is currently a timid approximation. Therefore, an accurate account and a new classification of Senna are part of my long-term goals.

Fig. 1 Diversity of habits in Senna. © B. Marazzi.

Current Projects

EFNs are secretory structures attracting ants and forming a protective opportunistic ant-plant interaction or mutualism [4] in some ferns and in over 90 angiosperm families, notably in the legume family [5, 6]. In Senna, EFNs are typically found on leaves (Fig. 2) and rarely also on pedicels. Species with EFNs form a large strongly supported clade within Senna, the ‘EFN clade’ (see Marazzi et al. 2006a), and EFNs seem thus to represent a morphological novelty in the genus, raising interesting questions on their evolutionary role:

Are EFNs a key innovation in plant defense strategies?

Key innovations are one of the most important triggers of large-scale diversifications and radiations in nature explaining unusual disparities between clades [7]. The observation of a conspicuous clade size difference between the ‘EFN clade’ and its sister clade lacking EFNs and the available ecological evidence of EFNs (and mutualism) to increase plant fitness, suggest that the EFNs have played a key role in the large-scale diversification of Senna (Marazzi et al. 2006a). It is the primary aim of my current project in Mike Sanderson’s Lab to test the hypotheses whether EFNs are a key innovation in Senna, in particular, and in angiosperms, in general. Read about the first results here.

Fig. 2 Examples of EFNs in Senna. © B. Marazzi.

**** 

LOOKING FOR AN UNDERGRAD RESEARCH PROJECT?

Several research subjects are available as part of my project on EFNs. They address fundamental questions on the ecological role, anatomy and morphology, and evolution of extrafloral nectaries in Senna. Some projects may include field work.  For questions and more information please email me.

****

Flowers of Senna are structurally highly diverse (Fig. 3), and have been the focus of my doctoral studies with Prof. Peter K. Endress (University of Zurich, Switzerland; co-advised by Prof. Elena Conti). They display an array of traits typically related to buzz pollination (i.e. bees vibrate the stamens to extract and collect the pollen [8]), such as poricidal anther dehiscence with unusual, long and tubular anther tips in some species, heteranthery with up to four different kinds of stamens and seven different kinds of heterantherous androecia, and point-tipped stigmas (Marazzi et al. 2007). This outstanding diversity makes the androecium of Senna an ideal example to illustrate the specializations that buzz flowers have undergone in conjunction with their pollination mode. Many species are further characterized by asymmetric, enantiostylous flowers, in which the entire carpel is deflected to the left or right (Fig. 3).

Asymmetric flowers are rare in angiosperms [9]. In Senna, floral asymmetry is complex: up to five floral organs out of three floral whorls (corolla, androecium, and gynoecium) directly affect the floral symmetry and form, in different combinations, up to five floral asymmetry patterns (Marazzi and Endress 2008). The presence of both species with monosymmetric and many diverse asymmetric flowers makes Senna an ideal group to study the evolution of floral asymmetry and character complexes.

Future work is aimed at reconstructing the evolution of floral structural specialization and floral asymmetry in Senna, testing also hypotheses of character state correlations to understand the multiple origins of highly asymmetric flowers.

Fig. 3 Diversity of flowers in Senna. © B. Marazzi.

Cassia s.str., Chamaecrista and Senna, which together currently comprise subtribe Cassiinae, were formerly known as Cassia s.l., previously one of the largest genera in Fabaceae, with ca. 700 species distributed worldwide. Up to five out of 30 Cassia species (spp.), 11 out of ca. 350 Chamaecrista spp., and 30 out of 300-350 Senna spp. are thought to occur in North America (NA; sensu Flora of North America, FNA).

This tentative assessment of species present in NA is the starting point for my ongoing taxonomic study for the FNA Vol 10-11, aimed at providing species descriptions, identification tools, and other information (e.g., distribution outside NA, particular uses, etc.) for species of these three genera. Most work for this project is carried out at the University of Arizona Herbarium (ARIZ).

Furthermore, a similar study will be done for the Legumes of Arizona Project, focusing on the species of Cassia s.str., Chamaecrista and Senna in the state of Arizona.

*** Literature cited is at the very end of the webpage ***

PUBLICATIONS

Research Publications (for PDFs of articles email me)

Marazzi, B., P. K. Endress (2008) Patterns and development of floral asymmetry in Senna (Leguminosae, Cassiinae). American Journal of Botany 95: 22-40. [abstract]

Marazzi, B., E. Conti, P. K. Endress (2007) Diversity of anthers and stigmas in the buzz-pollinated genus Senna (Leguminosae, Cassiinae). International Journal of Plant Science 168: 371-391. [abstract]

Marazzi, B., P. K. Endress, L. Paganucci de Queiroz, E. Conti (2006a) Phylogenetic relationships within Senna (Leguminosae, Cassiinae) based on three chloroplast regions: patterns in the evolution of floral symmetry and extrafloral nectaries. American Journal of Botany 93: 288-303. [abstract]

Marazzi, B., R. Fortunato, P. K. Endress, R. Spichiger (2006b) Senna (Cassiinae, Leguminosae) in Paraguay: synopsis, conservation, ecologic role and ethnobotany. Candollea 61: 315-329. [abstract]

Manuscripts in preparation

Marazzi, B., M. J. Sanderson. Large-scale patterns of diversification of Senna (Leguminosae) and the evolutionary role of extrafloral nectaries.

Marazzi, B. Cassia. For: Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 12+ vols. New York and Oxford. Vol. 10&11.

Marazzi, B. Chamaecrista. For: Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 12+ vols. New York and Oxford. Vol. 10&11.

Marazzi, B. Senna. For: Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 12+ vols. New York and Oxford. Vol. 10&11.

Abstracts

Marazzi, B. (2009) The legumes Cassia, Chamaecrista, and Senna in the Flora of North America. Botany 2009 Congress (Annual meeting of ABLS, AFS, ASPT and BSA), Snowbird - Salt Lake City, Utah, USA. Poster presentation abstract ID 1210. [see abstract here]

Marazzi, B., M.J. Sanderson (2009) Large-scale diversification patterns in the legume genus Senna and the evolutionary role of extrafloral nectaries. Botany 2009 Congress (Annual meeting of ABLS, AFS, ASPT and BSA), Snowbird - Salt Lake City, Utah, USA. Poster presentation abstract ID 1208. [see abstract here]

Marazzi, B., M.J. Sanderson (2008) Large-scale diversification of Senna (Leguminosae) in the American continent. Botany 2008 Congress (Annual meeting of ABLS, AFS, ASPT and BSA), Vancouver, Canada. Oral presentation abstract.

Marazzi, B., P. K. Endress (2007) Diversity, development and evolution of asymmetric flowers in Senna (Leguminosae). Botanikertagung 2007 (Annual meeting of the German Society of Botany), Hamburg, Germany. Poster abstract.

Marazzi, B., P. K. Endress (2007) Diversity, development and evolution of asymmetric flowers in Senna (Leguminosae). Abstract volume of the Botany 2007 Congress (Annual meeting of ABLS, AFS, ASPT and BSA), Chicago, Illinois, USA. Oral presentation abstract ID 999.

Marazzi, B., E. Conti, P. K. Endress (2006) Evolution of floral diversity in the buzz-pollinated genus Senna (Leguminosae, Cassiinae). Abstract volume of the Botany 2006 Congress (Annual meeting of ABLS, AFS, ASPT and BSA), Chico, California, USA. Oral presentation abstract ID119.

Marazzi, B., E. Conti, L. Paganucci de Queiroz, P. K. Endress (2005) Asymmetric flowers and phylogeny in Senna (Leguminosae, Cassiinae). Symposium of the Zurich-Basel Plant Science Center, Zurich, Switzerland. Poster abstract.

Marazzi, B., E. Conti, L. Paganucci de Queiroz, P. K. Endress (2005) Asymmetric flowers and phylogeny in Senna (Leguminosae, Cassiinae). Abstract volume of the XVII International Botanical Congress, Vienna, Austria. Poster abstract P0472, p. 314.

Marazzi, B., P. K. Endress, E. Conti (2004) Phylogeny and evolution of asymmetric flowers in Senna (Leguminosae, Cassiinae). Symposium “Challenges in Plant Science” in Zurich, Switzerland. Poster abstract. Winner of a poster award.

Marazzi, B., P. K. Endress, E. Conti (2004) Phylogeny and evolution of asymmetric flowers in Senna (Leguminosae, Cassiinae). Abstract volume of the Botany 2004 Congress (Annual meeting of ABLS, AFS, ASPT and BSA), Snowbird, Utah, USA. Poster Abstract ID207, p. 53.

CURRICULUM VITAE

NAP BOOK ON SCIENCE, EVOLUTION, AND CREATIONISM (2008)

Literature cited

[1] Irwin HS, RC Barneby 1982 Mem New York Bot Gard 35: 1-918.

[2] Colladon TF 1816 Histoire naturelle et médicale des casses[…]. Jean Martel, Montpellier.

[3] Luckow M 1996 Baileya 23: 195-241.

[4] Heil M, D McKey 2003 Annu Rev Ecol Evol Syst 34: 425-453.

[5] Koptur S 1992 Pages 81-129 in E Bernays (Ed.) Insect-plant interactions, volume IV. CRC Press, London.

[6] McKey D 1989 Pages 673–718 in CH Stirton, JL Zarucchi, eds. Advances in legume biology. Monogr Syst Bot Mo Bot Gard 29.

[7] Sanderson MJ, MJ Donoghue 1994 Science 264: 1590-1593.

[8] Buchmann SL 1983 Pages 73-113 in CE Jones, RJ Little, eds. Handbook of experimental pollination biology. Scientific and Academic Editions, New York.

[9] Endress PK 1999 Int J Plant Sci 160 (Suppl, 6):S3-S23.

[10] Lewis J, B Schrire, B Mackinder, M Lock 2005 Legumes of the world. Royal Botanic Garden, Kew.

Last updated: 02 Nov. 2009 - Copyright Brigitte Marazzi.