Valid proof of COVID-19 vaccination and ID is required for entry to indoor exhibition spaces and facilities, and all dining areas. Learn more.

Image of the Library Building

William Wayt Thomas

Curator Emeritus, Institute of Systematic Botany

Ph.D., University of Michigan
Ann Arbor, Michigan, 1982


Cyperaceae (Sedge family), Simaroubaceae (Tree of Heaven family, and Picramniaceae (Bitter-bush Family)
Flora and conservation of the Atlantic forest of northeastern Brazil


Systematics of Cyperaceae, Simaroubaceae, and Picramniaceae; flora of the Atlantic Coastal forests of Brazil

Research locations

Brazil (especially the Atlantic coastal forest), neotropics, worldwide


The focus of my research is plants of the American tropics, especially Brazil. I have three primary interests: the vegetation and conservation of the Atlantic coastal forests of northeastern Brazil; systematics of the Sedge family (Cyperaceae), especially the beaked-rushes (Rhynchospora); and the systematics of the Tree-of-Heaven family (Simaroubaceae and its segregate families, Picramniaceae and Surianaceae). I believe that systematic research provides a much-needed foundation for conservation of biodiversity. To that end, my work in northeastern Brazil is made available to local conservation organizations and has had a significant impact on conservation in the region.

Selected Publications

Sivadas, D. & W.W. Thomas. 2019. A reinvestigation on the taxonomic identity of Rhynchospora panduranganii (Cyperaceae). Phytotaxa 387 (3): 249-254. DOI: 10.11646/phytotaxa.387.3.5

Rozendaal, Danaë M.A., Frans Bongers, … Wayt Thomas, … Lourens Poorter. 2019. Biodiversity recovery of Neotropical secondary forests, Science Advances 5(3), eaau3114. DOI: 10.1126/sciadv.aau3114

Roalson, E. H., A. P. Prata, A. Mesterházy, M. W. Chase, D. A. Simpson, W. W. Thomas, and I. Larridon. 2019. A broader circumscription of Bulbostylis (Abildgaardieae: Cyperaceae). Phytotaxa 395 (3): 199-208. DOI: 10.11646/phytotaxa.395.3.4

Poorter, Lourens, Danaë M.A. Rozendaal, Frans Bongers, … William Wayt Thomas, … Mark Westoby. 2019. Wet and dry tropical forests show opposite successional pathways in wood density but converge over time. Nature Ecology & Evolution . DOI: 10.1038/s41559-019-0882-6.

Silva Filho, P. J. S., W. W. Thomas and I. I. Boldrini. 2019. Two new endemic species of Rhynchospora (Cyperaceae) section Tenues from Bahia, Brazil. Systematic Botany 44(3): 652-658. DOI: 10.1600/036364419X15620113920671

Nunes, C. S., P.J. S. Silva Filho, W. W. Thomas & A.S. B. Gil. 2019. Rhynchospora seccoi, a new species of Rhynchospora sect. Tenues (Cyperaceae) from the Brazilian Amazon (Serra dos Carajás, Pará State). Phytotaxa 405 (2): 91-100. DOI: 10.11646/phytotaxa.405.2.4

Soares Neto, R.L., W.W. Thomas, M. R. V. Barbosa, E. H. Roaslon. 2019. A well-known “mussambê” is a new species of Tarenaya (Cleomaceae) from South America. Systematic Botany 44(3): 686-691. DOI: 10.1600/036364419X15620113920743

Devecchi, M. F., W. W. Thomas and J. R. Pirani. 2018. Two new dwarf species of Homalolepis (Simaroubaceae) from the Brazilian Cerrado (Neotropical savanna). Phytotaxa 336(3): 252-262. DOI: 10.11646/phytotaxa.336.3.3
Costa, A.C.G., I.S. Albuquerque, W.W. Thomas, & I.C. Machado. 2018. Influence of environmental variation on the pollination of the ambophilous sedge Rhynchospora ciliata (Cyperaceae) Plant Ecology 219: 241-250.

Devecchi, M. F., W. W. Thomas, and J. R. Pirani. 2018. Disentangling the problematic Simaba ferruginea species complex (Simaroubaceae), with description of a new species from dry forests of northern South America. Systematic Botany 43: 557-570. DOI: 10.1600/036364418X697283

Soares Neto, R. L., W. W. Thomas, M. R.V. Barbosa & E. H. Roalson. 2018. New combinations and taxonomic notes in Tarenaya (Cleomaceae). Acta Botanica Brasilica 32(4), DOI: 10.1590/0102-33062017abb0417

Thomas, W.W. 2018. Trust and the power of global collaborative projects. Taxon 67(6): 1062-1063. DOI: 10.12705/676.3.

Silva Filho, P. J., W. W. Thomas & I. I. Boldrini. 2018. Two new species of Rhynchospora (Cyperaceae) from Southern Brazil. Phytotaxa 383(1). DOI: 10.11646/phytotaxa.383.1.8

Costa, A.C.G., W.W. Thomas and I.C. Machado. 2017. Comparative floral biology of Rhynchospora ciliata (Vahl) Kükenth. and R. pubera (Vahl) Boeckeler (Cyperaceae): the role of white involucral bracts in attracting pollinating insects. Plant Species Biology. DOI: 10.1111/1442-1984.12173

Buddenhagen, Christopher E., W. Wayt Thomas and Austin R. Mast. 2017. A First Look at Diversification of Beaksedges (Tribe Rhynchosporeae; Cyperaceae) in habitat, pollination, and photosynthetic features. In: Diversity and Phylogeny of the Monocotyledons, Contributions from Monocots V. Memoirs of the New York Botanical Garden 118: 113-126. DOI: 10.21135/893275341.002.

Ribeiro, T., C. Buddenhagen, W. Thomas, G. Souza and A. Pedrosa-Harand. 2017. Are holocentrics doomed to change? Limited chromosome number variation in Rhynchospora Vahl (Cyperaceae). Protoplasma 2017. DOI: 10.1007/s00709-017-1154-4

Thomas, W. W. and P. J. S. Silva Filho. 2017. Rhynchospora rheophytica (Cyperaceae), a new species of from western Bahia, Brazil. Brittonia 70: 60-64. DOI: 10.1007/s12228-017-9499-8

Devecchi, M. F., W. W. Thomas, G. M. Plunkett and J. R. Pirani. 2017. Testing the monophyly of Simaba (Simaroubaceae): Evidence from five molecular markers and morphology. Molecular Phylogenetics and Evolution 120: 63-82.

Saiter, F. Z., J. L Brown, W. W. Thomas, A. T. Oliveira-Filho and A. C. Carnaval,. 2016. Environmental correlates of floristic regions and plant turnover in the Atlantic Forest hotspot. Journal of Biogeography. 43: 2322–2331, DOI: 10.1111/jbi.12774

Thomas, W. W. 2016. 125 years of floristic research and collecting at The New York Botanical Garden. Brittonia 68: DOI: 10.1007/s12228-016-9413-9

Devecchi, M. F., W. W. Thomas and J. R. Pirani. 2016. Simaba arenaria (Simaroubaceae): a New Species from Sandy Coastal Plains in Northeastern Brazil, with Notes on Seedling Morphology. Systematic Botany 41(2): 401-407. DOI: 10.1600/036364416X691885

Bonet Mayedo, W. and W. W. Thomas. 2016. Two New Species of Scleria section Hypoporum (Cyperaceae) from Espírito Santo, Brazil. Phytotaxa 268 (4): 263–270. DOI: 10.11646/phytotaxa.268.4.4.

Ganzhorn, S.M., B. Perez-Sweeney, W.W. Thomas, F.A. Gaiotto, and J.D. Lewis. 2015. The effects of fragmentation on density and population genetics of a threatened tree species in a biodiversity hotspot. Endangered Species Research 01/2015; 26:189-199. DOI: 10.3354/esr00645.

Saiter, F. Z., P. V. Eisenlohr, M. R. V. Barbosa, W. W. Thomas, and A. T. Oliveira-Filho. 2015. From evergreen to deciduous tropical forests: how energy-water balance, temperature, and space influence the tree composition in a high diversity region. Plant Ecology and Biodiversity. DOI:10.1080/17550874.2015.1075623

Nusbaumer, L., M. R. V. Barbosa, W. W. Thomas, M. V. Alves, P.-A. Loizeau & R. Spichiger. 2015. Flora e vegetação da Reserva Biológica de Pedra Talhada. In: Studer, A., L. Nusbaumer & R. Spichiger (Eds.). Biodiversidade da Reserva Biológica de Pedra Talhada (Alagoas, Pernambuco – Brasil). Boissiera 68: 59-121.

Thomas, W. W. and M. Tulig. 2015. Hard Copy to Digital: Flora Neotropica and the World Flora Online. Rodriguésia 66(4): 983-987. DOI: 10.1590/2175-7860201566404.

Saiter, F., P. V. Eisenlohr, G. S. França, J. R. Stehmann, W. W. Thomas, and A. T. Oliveira-Filho. 2015. Floristic units and their predictors unveiled in part of the Atlantic Forest hotspot: implications for conservation planning. Anais da Academia Brasileira de Ciências. 87(4): 2031-2046. DOI: 10.1590/0001-3765201520140132

Ganzhorn, S.G., W.W. Thomas, F.A. Gaiotto, and J.D. Lewis. 2015. Spatial genetic structure of Manilkara maxima: A threatened tree species from the Brazilian Atlantic forest. Journal of Tropical Ecology 31 (5): 437-447. DOI: 10.1017/S0266467415000292.

Araújo, A. C., H. M. Longhi-Wagner and W. W. Thomas. 2012. A Synopsis of Rhynchospora sect. Pluriflorae (Cyperaceae). Brittonia 64: 381-393.

Thomas, W. W. 2011. Nothotalisia, a new genus of Picramniaceae from tropical America. Brittonia 63: 51-61. DOI: 10.1007/s12228-010-9130-8.

Alves, M., A. C. Araújo, A. P. Prata, F. Vitta, S. Hefler, R. Trevisan, A. S. Bragança Gil, S. Martins & W. Thomas. 2009 (2010). Diversity of Cyperaceae in Brazil. Rodriguésia 60(4): 771-782 and Appendix pp. 1-60, online.

Thomas, W. W., J. G. Jardim, P. Fiaschi, M. Mariano-Neto and A. M. Amorim. 2009. Composição Florística e Estrutura do Componente Arbóreo de uma Área Transicional de Floresta Atlântica no Sul da Bahia, Brasil. Revista Brasileira de Botânica 32 (1): 41-54.

Piotto, D., F. Montagnini, W. Thomas, M. Ashton and C. Oliver. 2009. Forest recovery after swidden cultivation across a 40-year chronosequence in the Atlantic forest of southern Bahia, Brazil. Plant Ecology 205: 261-272. DOI 10.1007/s11258-009-9615-2.

Thomas, W. W., Araújo, A. C., and M. Alves. 2009 (2008 online). A Preliminary Molecular Phylogeny of the Rhynchosporeae (Cyperaceae). In: W. W. Thomas, D. A. Simpson, A. A. Reznicek and J. R. Starr (eds.), Cyperaceae – Special Issue. Botanical Review 75: 22-29, DOI 10.1007/s12229-008-9023-7.

Thomas, W. W. (ed.). 2008. The Atlantic Coastal Forest of Northeastern Brazil. Memoirs New York Botanical Garden 100: 1-586.

Amorim, A. M., W. W. Thomas, A. M. de Carvalho and J. G. Jardim. 2008. Floristics of the Una Biological Reserve, Bahia, Brazil. In: W. Thomas (ed.), The Atlantic Coastal Forest of Northeastern Brazil. Memoirs of the New York Botanical Garden 100: 67-146.

Mattos Silva, L. A., J. G. Jardim, W. W. Thomas, and T. S. dos Santos. 2008. Common Names of Vascular Plants of the Atlantic Coastal Forest Region of Southern Bahia, Brazil. In: W. Thomas (ed.), The Atlantic Coastal Forest of Northeastern Brazil. Memoirs of the New York Botanical Garden 100: 245-318.

Thomas, W. W. and M. R. V. Barbosa. 2008. Natural Vegetation Types in the Brazilian Atlantic Coastal Forest North of the Rio Doce. In: W. Thomas (ed.), The Atlantic Coastal Forest of Northeastern Brazil. Memoirs of the New York Botanical Garden 100: 6-20.

Thomas, W. W., A. M. de Carvalho, A. M. A. Amorim, J. Garrison, T. S. dos Santos. 2008. Diversity of Woody Plants in the Atlantic Coastal Forest of Southern Bahia, Brazil. In: W. Thomas (ed.), The Atlantic Coastal Forest of Northeastern Brazil. Memoirs of the New York Botanical Garden 100: 21-66.

Simpson, D. A., A. M. Muasya, M. Alves, J. J. Bruhl, S. Dhooge, M. W. Chase, C. A. Furness, K. Ghamkhar, P. Goetghebeur, T. R. Hodkinson, A. D. Marchant, R. Nieuwborg, A. A. Reznicek, E. H. Roalson, E. Smets, J. R. Starr, W. W. Thomas, K. L. Wilson & X. Zhang. 2007 [2008]. Phylogeny of Cyperaceae based on DNA sequence data – a new rbcL analysis. In: J. T. Columbus, E.A. Friar, J.M. Porter, L.M. Prince, and M.G. Simpson (eds.), Monocots, Comparative Biology and Evolution (Poales). Aliso 23:72-83.

Thomas, W. W. 2002. Simaroubaceae. Pages . In: S. Mori, C. Gracie, J. Mitchell, J.-J. de Granville and G. Cremers (eds.), Guide to the Vascular Plants of Central French Guiana, Part 2. Dicotyledons. The New York Botanical Garden, New York.

Thomas, W. W. 1999. Conservation and monographic research on the flora of tropical America. Biodiversity and Conservation 8: 1007-1015.

Thomas, W. W. 1998. Rhynchospora (Cyperaceae). Pages 610-629, In: (J. A. Steyermark, P. E. Berry, and B. K. Holst, eds.) Flora of the Venezuelan Guayana, Volume 4, Caesalpiniaceae-Ericaceae. Missouri Botanical Garden Press, St. Louis.

Thomas, W. W., A. M. de Carvalho, A. M. Amorim, J. Garrison and A. L. Arbeláez. 1998. Plant endemism in two forests in southern Bahia, Brazil. Biodiversity and Conservation 7(3): 311-322.

Thomas, W. W. 1994. Rhynchospora, Cyperaceae. Pp. 404-422, In: G. Davidse, M. Sousa S. and A. O. Chater (general eds.), Flora Mesoamericana, Volumen 6, Alismataceae to Cyperaceae. Inst. de Biología, Univ. Nac. Autónoma de México, México.

Thomas, W. W. 1988. A conspectus of Mexican and Central American Picramnia (Simaroubaceae). Brittonia 40(1): 89-105.

Thomas, W. W. 1984. The systematics of Rhynchospora section Dichromena (Cyperaceae). Mem. New York Bot. Gard. 37: 1-116.