Advances in Legume Systematics 14. Classification of Caesalpinioideae. Part 2: Higher-level classification Author Bruneau, Anne https://orcid.org/0000-0001-5547-0796 Institut de recherche en biologie vegetale and Departement de Sciences biologiques, Universite de Montreal, 4101 Sherbrooke E., Montreal (QC) H 1 X 2 B 2, Canada anne.bruneau@umontreal.ca Author de Queiroz, Luciano Paganucci https://orcid.org/0000-0001-7436-0939 Universidade Estadual de Feira de Santana, Departamento de Ciencias Biologicas, Av. Transnordestina s / n, Campus, Novo Horizonte. 44036 - 900, Feira de Santana, BA, Brazil Author Ringelberg, Jens J. https://orcid.org/0000-0003-0567-5210 Department of Systematic and Evolutionary Botany, University of Zurich, Zollikerstrasse 107, 8008 Zurich, Switzerland & School of Geosciences, University of Edinburgh, Old College, South Bridge, Edinburgh EH 8 9 YL, UK Author Borges, Leonardo M. https://orcid.org/0000-0001-9269-7316 Universidade Federal de Sao Carlos, Departamento de Botanica, Rodovia Washington Luis, Km 235, 13565 - 905, Sao Carlos, SP, Brazil Author Bortoluzzi, Roseli Lopes da Costa https://orcid.org/0000-0002-7445-7244 Programa de Pos-graduacao em Producao Vegetal, Universidade do Estado de Santa Catarina, Centro de Ciencias Agroveterinarias, Avenida Luiz de Camoes 2090, 88520 - 000, Lages, Santa Catarina, Brazil Author Brown, Gillian K. https://orcid.org/0000-0002-7940-5435 Queensland Herbarium and Biodiversity Science, Department of Environment and Science, Toowong, Queensland, 4066, Australia Author Cardoso, Domingos B. O. S. https://orcid.org/0000-0001-7072-2656 Instituto de Pesquisas Jardim Botanico do Rio de Janeiro, Pacheco Leao 915, 22460 - 030, Rio de Janeiro, RJ, Brazil & Programa de Pos-Graduacao em Biodiversidade e Evolucao (PPGBioEvo), Instituto de Biologia, Universidade Federal de Bahia (UFBA), Rua Barao de Jeremoabo, s. n., Ondina, 40170 - 115, Salvador, BA, Brazil Author Clark, Ruth P. https://orcid.org/0000-0001-9974-2933 Accelerated Taxonomy Department, Royal Botanic Gardens, Kew, Richmond, TW 9 3 AE, UK Author Conceicao, Adilva de Souza https://orcid.org/0000-0002-8800-422X Programa de Pos-graduacao em Diversidade Vegetal, Universidade do Estado da Bahia, Herbario HUNEB, Campus VIII, Rua do Gangorra 503, 48608 - 240, Paulo Afonso, Bahia, Brazil Author Cota, Matheus Martins Teixeira https://orcid.org/0000-0003-0654-7501 Universidade Estadual de Feira de Santana, Departamento de Ciencias Biologicas, Av. Transnordestina s / n, Campus, Novo Horizonte. 44036 - 900, Feira de Santana, BA, Brazil Author Demeulenaere, Else https://orcid.org/0000-0002-1815-3051 Center for Island Sustainability and Sea Grant, University of Guam, UOG Station, Mangilao, 96923, Guam Author de Stefano, Rodrigo Duno https://orcid.org/0000-0003-1707-4121 Centro de Investigacion Cientifica de Yucatan, A. C. (CICY), Calle 43 No. 130 x 32 y 34, Chuburna de Hidalgo; CP 97205, Merida, Yucatan, Mexico Author Ebinger, John E. Eastern Illinois University, Charleston, IL 61920, USA Author Ferm, Julia https://orcid.org/0000-0002-8762-3942 Department of Ecology, Environment and Plant Sciences, 10691, Stockholm University, Stockholm, Sweden Author Fonseca-Cortes, Andres https://orcid.org/0000-0001-7207-9940 Universidade Estadual de Feira de Santana, Departamento de Ciencias Biologicas, Av. Transnordestina s / n, Campus, Novo Horizonte. 44036 - 900, Feira de Santana, BA, Brazil Author Gagnon, Edeline https://orcid.org/0000-0003-3212-9688 Department of Integrative Biology, University of Guelph, 50 Stone Road, Guelph (ON) N 1 G 2 W 1, Canada & Chair of Phytopathology, Technical University Munich, 85354 Freising, Germany & Royal Botanic Garden Edinburgh, 20 A Inverleith Row, Edinburgh, EH 3 5 LR, UK Author Grether, Rosaura https://orcid.org/0000-0003-2673-665X Departamento de Biologia, Universidad Autonoma Metropolitana-Iztapalapa, Apdo. Postal 55 - 535, 09340 Ciudad de Mexico, Mexico Author Guerra, Ethiene https://orcid.org/0000-0002-9495-1717 Universidade Federal do Rio Grande do Sul, Programa de Pos-Graduacao em Botanica, Av. Bento Goncalves 9500, Bloco IV - Predio 43433, Porto Alegre, RS, 91501 - 970, Brazil Author Haston, Elspeth https://orcid.org/0000-0001-9144-2848 Royal Botanic Garden Edinburgh, 20 A Inverleith Row, Edinburgh, EH 3 5 LR, UK Author Herendeen, Patrick S. https://orcid.org/0000-0003-2657-8671 Chicago Botanic Garden, 1000 Lake Cook Road, Glencoe, IL 60022, USA Author Hernandez, Hector M. https://orcid.org/0000-0002-1741-5515 Departamento de Botanica, Instituto de Biologia, Universidad Nacional Autonoma de Mexico, Cd. Universitaria, 04510 Ciudad de Mexico, Mexico Author Hopkins, Helen C. F. https://orcid.org/0000-0003-4984-8224 Accelerated Taxonomy Department, Royal Botanic Gardens, Kew, Richmond, TW 9 3 AE, UK Author Huamantupa-Chuquimaco, Isau https://orcid.org/0000-0002-4153-5875 Herbario Alwyn Gentry (HAG), Universidad Nacional Amazonica de Madre de Dios (UNAMAD), AV. Jorge Chavez N ° 1160, Madre de Dios, Peru Author Hughes, Colin E. https://orcid.org/0000-0002-9701-0699 Department of Systematic and Evolutionary Botany, University of Zurich, Zollikerstrasse 107, 8008 Zurich, Switzerland Author Ickert-Bond, Stefanie M. https://orcid.org/0000-0001-8198-8898 Department of Biology & Wildlife & Herbarium (ALA) at the University of Alaska Museum of the North, University of Alaska Fairbanks, P. O. Box 756960, Fairbanks AK 99775 - 6960, USA Author Iganci, Joao https://orcid.org/0000-0002-5740-3666 Universidade Federal do Rio Grande do Sul, Programa de Pos-Graduacao em Botanica, Av. Bento Goncalves 9500, Bloco IV - Predio 43433, Porto Alegre, RS, 91501 - 970, Brazil & Programa de Pos-Graduacao em Fisiologia Vegetal, Universidade Federal de Pelotas, Instituto de Biologia, Campus Universitario Capao do Leao, Passeio Andre Dreyfus, Departamento de Botanica, Predio 21, Pelotas, Rio Grande do Sul, 96010 - 900, Brazil Author Koenen, Erik J. M. https://orcid.org/0000-0002-4825-4339 Evolutionary Biology & Ecology, Universite Libre de Bruxelles, Faculte des Sciences, Campus du Solbosch - CP 160 / 12, Avenue F. D. Roosevelt, 50, 1050 Bruxelles, Belgium Author Lewis, Gwilym P. https://orcid.org/0000-0003-2599-4577 Accelerated Taxonomy Department, Royal Botanic Gardens, Kew, Richmond, TW 9 3 AE, UK Author de Lima, Haroldo Cavalcante https://orcid.org/0000-0003-2154-670X Instituto de Pesquisas Jardim Botanico do Rio de Janeiro, Pacheco Leao 915, 22460 - 030, Rio de Janeiro, RJ, Brazil & Instituto Nacional da Mata Atlantica / INMA-MCTI, Av. Jose Ruschi, 4, Centro, 29650 - 000, Santa Teresa, Espirito Santo, Brazil Author de Lima, Alexandre Gibau https://orcid.org/0000-0002-9168-2507 Instituto de Pesquisas Jardim Botanico do Rio de Janeiro, Pacheco Leao 915, 22460 - 030, Rio de Janeiro, RJ, Brazil & Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, Sweden Author Luckow, Melissa https://orcid.org/0009-0007-2543-0516 School of Integrative Plant Science, Plant Biology Section, Cornell University, 215 Garden Avenue, Roberts Hall 260, Ithaca, NY 14853, USA Author Marazzi, Brigitte https://orcid.org/0000-0003-3252-5816 Natural History Museum of Canton Ticino, Viale C. Cattaneo 4, 6900 Lugano, Switzerland Author Maslin, Bruce R. https://orcid.org/0000-0002-3039-0973 Western Australian Herbarium, Department of Biodiversity, Conservation and Attractions, Locked Bag 104, Bentley Delivery Centre, Western Australia, 6983, Australia & Singapore Herbarium, 1 Cluny Road, Singapore, Singapore Author Morales, Matias https://orcid.org/0000-0001-5540-9725 Instituto de Recursos Biologicos, CIRN-CNIA, INTA. N. Repetto & Los Reseros s. n., Hurlingham, Buenos Aires, Argentina & Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Godoy Cruz 2290 (C 1425 FQB), Ciudad Autonoma de Buenos Aires, Argentina Author Morim, Marli Pires https://orcid.org/0000-0003-0872-8429 Instituto de Pesquisas Jardim Botanico do Rio de Janeiro, Pacheco Leao 915, 22460 - 030, Rio de Janeiro, RJ, Brazil Author Murphy, Daniel J. https://orcid.org/0000-0002-8358-363X Royal Botanic Gardens Victoria, Melbourne, Victoria, 3004, Australia Author O'Donnell, Shawn A. https://orcid.org/0000-0003-0731-7425 Geography and Environmental Sciences, Northumbria University, Ellison Place, Newcastle upon Tyne, NE 1 8 ST, UK Author Oliveira, Filipe Gomes https://orcid.org/0000-0003-0244-3262 Universidade Estadual de Feira de Santana, Departamento de Ciencias Biologicas, Av. Transnordestina s / n, Campus, Novo Horizonte. 44036 - 900, Feira de Santana, BA, Brazil Author Oliveira, Ana Carla da Silva https://orcid.org/0000-0001-7042-5360 Universidade Estadual de Feira de Santana, Departamento de Ciencias Biologicas, Av. Transnordestina s / n, Campus, Novo Horizonte. 44036 - 900, Feira de Santana, BA, Brazil Author Rando, Juliana Gastaldello https://orcid.org/0000-0002-3714-8231 Programa de Pos-graduacao em Ciencias Ambientais, Universidade Federal do Oeste da Bahia, Rua Professor Jose Seabra Lemos 316, 47800 - 021, Barreiras, Bahia, Brazil Author Ribeiro, Petala Gomes https://orcid.org/0000-0002-0070-9971 Universidade Estadual de Feira de Santana, Departamento de Ciencias Biologicas, Av. Transnordestina s / n, Campus, Novo Horizonte. 44036 - 900, Feira de Santana, BA, Brazil Author Ribeiro, Carolina Lima https://orcid.org/0000-0001-9508-2894 Universidade Estadual de Feira de Santana, Departamento de Ciencias Biologicas, Av. Transnordestina s / n, Campus, Novo Horizonte. 44036 - 900, Feira de Santana, BA, Brazil Author Santos, Felipe da Silva https://orcid.org/0000-0002-1068-0578 Universidade Estadual de Feira de Santana, Departamento de Ciencias Biologicas, Av. Transnordestina s / n, Campus, Novo Horizonte. 44036 - 900, Feira de Santana, BA, Brazil Author Seigler, David S. https://orcid.org/0009-0003-5177-5893 Department of Plant Biology, University of Illinois, Urbana, IL 61801, USA Author da Silva, Guilherme Sousa https://orcid.org/0000-0002-4250-0017 Instituto de Biologia, Universidade Estadual de Campinas, Campinas, 13083 - 876, Sao Paulo / SP, Brazil Author Simon, Marcelo F. https://orcid.org/0000-0002-5732-1716 Empresa Brasileira de Pesquisa Agropecuaria (Embrapa) Recursos Geneticos e Biotecnologia, Parque Estacao Biologica, Caixa Postal 02372, 70770 - 917, Brasilia / DF, Brazil Author Soares, Marcos Vinicius Batista https://orcid.org/0000-0003-2660-1771 Universidade Federal do Rio Grande do Sul, Programa de Pos-Graduacao em Botanica, Av. Bento Goncalves 9500, Bloco IV - Predio 43433, Porto Alegre, RS, 91501 - 970, Brazil Author Terra, Vanessa https://orcid.org/0000-0001-5669-1304 Instituto de Biologia, Universidade Federal de Santa Maria, 97105 - 900, Santa Maria / RS, Brazil text PhytoKeys 2024 2024-04-03 240 1 552 http://dx.doi.org/10.3897/phytokeys.240.101716 journal article http://dx.doi.org/10.3897/phytokeys.240.101716 1314-2003-240-1 B699D9DE2B435B1093DE3C38C703D430 Senna Mill., Gard. Dict. Abr. (ed. 4). 1754. Figs 22 , 32 , 33 Chamaecassia Link, Handbuch 2: 139. 1831. Type: Chamaecassia laevigata (Willd.) Link [≡ Cassia laevigata Willd. (= Senna septemtrionalis (Viv.) H.S. Irwin & Barneby)] Chamaefistula (DC. ex Collad.) G. Don, Gen. Hist. 2: 106. 1832. Type: Chamaefistula corymbosa (Lam.) G. Don [≡ Cassia corymbosa Lam. (≡ Senna corymbosa (Lam.) H.S. Irwin & Barneby)] Adipera Raf., Sylva Tellur.: 129. 1838. Type: Adipera herbertiana (Lindl.) Raf. [= Senna x floribunda (Cav.) H.S. Irwin & Barneby] Diallobus Raf., Sylva Tellur.: 128. 1838. Type: Diallobus tora (L.) Raf. [≡ Cassia tora L. (≡ Senna tora (L.) Roxb.)] Ditremexa Raf., Sylva Tellur.: 127. 1838. Lectotype (designated by Britton and Wilson 1924): Ditremexa occidentalis (L.) Britton & Rose [≡ Cassia occidentalis L. (≡ Senna occidentalis (L.) Link)] Emelista Raf., Sylva Tellur.: 127. 1838. Type: Emelista obtusifolia (L.) Raf. [≡ Cassia obtusifolia L. (≡ Senna obtusifolia (L.) H.S. Irwin & Barneby)] Herpetica Raf., Sylva Tellur.: 123. 1838. Type: Herpetica alata (L.) Raf. [≡ Cassia alata L. (≡ Senna alata (L.) Roxb.)] Isandrina Raf., Sylva Tellur.: 126. 1838. Type: Isandrina arborescens Raf. [= Senna atomaria (L.) H.S. Irwin & Barneby] Panisia Raf., Sylva Tellur.: 128. 1838. Type: Panisia biflora (L.) Raf. [≡ Cassia Panisia biflora L., but typus not established, probably either = Senna pallida (Vahl) H.S. Irwin & Barneby sensu lato or S. angustisiliqua (Lam.) H.S. Irwin & Barneby] Peiranisia Raf., Sylva Tellur.: 127. 1838. Type: Peiranisia aversiflora (Herb.) Raf. [≡ Cassia aversiflora Herb. (≡ Senna aversiflora (Herb.) H.S. Irwin & Barneby)] Scolodia Raf., Sylva Tellur.: 128. 1838. Type: Scolodia viminea (L.) Raf. [≡ Cassia viminea L. (≡ Senna viminea (L.) H.S. Irwin & Barneby)] Cassia subg. Senna (Mill.) Benth., Fl. Bras. 15(2): 83, 96. 1870. Type not cited, but inferred as Senna alexandrina Mill. Chamaesenna Raf. ex Pittier, Arb. Arbus. Orden Legum.: 130. 1928. Lectotype (designated by Britton and Rose 1930 ): Chamaesenna reticulata (Willd.) Pittier [≡ Cassia reticulata Willd. (≡ Senna reticulata (Willd.) H.S. Irwin & Barneby)] Cowellocassia Britton, N. Amer. Fl. 23: 251. 1930. Type: Cowellocassia scleroxyla (Britton) Britton [≡ Cassia scleroxyla Britton (= Senna domingensis (Spreng.) H.S. Irwin & Barneby)] Earleocassia Britton, N. Amer. Fl. 23: 247. 1930. Type: Earleocassia roemeriana (Scheele) Britton [≡ Cassia roemeriana Scheele (≡ Senna roemeriana (Scheele) H.S. Irwin & Barneby)] Echinocassia Britton & Rose, N. Amer. Fl. 23: 251. 1930. Type: Echinocassia aculeata (Pohl ex Benth.) Britton & Rose [≡ Cassia aculeata Pohl ex Benth. (≡ Senna aculeata (Pohl ex Benth.) H.S. Irwin & Barneby)] Desmodiocassia Britton & Rose, N. Amer. Fl. 23: 244. 1930. Type: Desmodiocassia villosa (Mill.) Britton & Rose [≡ Cassia villosa Mill. (≡ Senna villosa (Mill.) H.S. Irwin & Barneby] Gaumerocassia Britton, N. Amer. Fl. 23: 252. 1930. Type: Gaumerocassia peralteana (Kunth) Britton [≡ Cassia peralteana Kunth (≡ Senna peralteana (Kunth) H.S. Irwin & Barneby)] Leonocassia Britton, N. Amer. Fl. 23: 268. 1930. Type: Leonocassia stenophylla (Benth.) Britton [≡ Cassia stenophylla Benth. (≡ Senna stenophylla (Benth.) H.S. Irwin & Barneby)] Palmerocassia Britton, N. Amer. Fl. 23: 253. 1930. Type: Palmerocassia wislizeni (A. Gray) Britton [≡ Cassia wislizeni A. Gray (≡ Senna wislizeni (A. Gray) H.S. Irwin & Barneby)] Phragmocassia Britton & Rose, N. Amer. Fl. 23: 245. 1930. Type: Phragmocassia skinneri (Benth.) Britton & Rose [≡ Cassia skinneri Benth. (≡ Senna skinneri (Benth.) H.S. Irwin & Barneby)] Pseudocassia Britton & Rose, N. Amer. Fl. 23: 230. 1930. Lectotype (designated by Irwin and Barneby 1982 ): Pseudocassia spectabilis (DC.) Britton & Rose [≡ Cassia spectabilis DC. (≡ Senna spectabilis (DC.) H.S. Irwin & Barneby)] Pterocassia Britton & Rose, N. Amer. Fl. 23: 243. 1930. Type: Pterocassia galeottiana (M. Martens) Britton & Rose [≡ Cassia galeottiana M. Martens (≡ Senna galeottiana (M. Martens) H.S. Irwin & Barneby)] Tharpia Britton & Rose, N. Amer. Fl. 23: 246. 1930. Type: Tharpia pumilio (A. Gray) Britton & Rose [≡ Cassia pumilio A. Gray (≡ Senna pumilio (A. Gray) H.S. Irwin & Barneby)] Vogelocassia Britton, N. Amer. Fl. 23: 258. 1930. Type: Vogelocassia leiophylla (Vogel) Britton [≡ Cassia leiophylla Vogel (≡ Senna leiophylla (Vogel) H.S. Irwin & Barneby)] Xerocassia Britton & Rose, N. Amer. Fl. 23: 246. 1930. Type: Xerocassia armata (S. Watson) Britton & Rose [≡ Cassia armata S.Watson (≡ Senna armata (S. Watson) H.S. Irwin & Barneby)] Type . Senna alexandrina Mill. Description. Trees, treelets, erect or scandent shrubs, subshrubs, vines, rarely aphyllous shrubs with cladode-like branches, unarmed or rarely with spines or prickles. Stipules diverse, caducous or persistent, rarely with embedded extrafloral nectary tissue. Leaves distichous or spiral, bifoliolate or paripinnate, rarely absent or reduced to a petiolar phyllode; extrafloral nectaries when present, on the petiole and/or on the leaf rachis, sessile or stipitate, the secretory surface convex; leaflets 1-many pairs, opposite. Inflorescences racemes or panicles; bract 1, persistent or caducous, bracteoles absent. Flowers hypogynous, bilaterally symmetrical or asymmetrical; hypanthium absent; sepals 5, free; petals 5, free, yellow; androecium comprising 3 adaxial staminodes and (4) 6-7 heteromorphic stamens, grouped in 2 sets of 4 median and (0) 2-3 abaxial stamens, rarely all 10 stamens fertile and homomorphic, filaments glabrous, anthers apically poricidal; pollen prolate-spheroidal to prolate, not syncopate; ovary stipitate. Fruit an indehiscent legume, a follicle or a legume dehiscing through both margins, linear or oblong, cylindrical, laterally compressed or tetragonal, fleshy or dry. Seeds variable in shape and colour. Chromosome number. Haploid chromosome numbers n = 11, 12, 13, 14 and 28 ( Goldblatt and Johnson 1979 -), but n = 14 is the most frequent. A single accession of S. rugosa (G.Don) H.S. Irwin & Barneby was found to be tetraploid with n = 28 ( Biondo et al. 2005b ), in contrast to Coleman and Demenezes (1980) who reported n = 14 for this species. Included species and geographic distribution. 287 species ( LPWG 2022 ), most species distributed on the American continent, occurring in tropical, subtropical and (few) temperate areas ( Irwin and Barneby 1982 ; Marazzi et al. 2006 ). Some species also distributed in Africa, Oceania and Asia ( Lock 1988 ; Du Puy 1995; Randell 1988 ; Randell and Barlow 1998 ; Fig. 33 ). Figure 32. Examples of Senna diversity A Senna macranthera (DC. ex Collad.) H.S. Irwin & Barneby flowering branch ( Lima et al. 422 ) B Senna alata (L.) Roxb. flowering branch C Senna corifolia (Benth.) H.S. Irwin & Barneby flowering branch ( Rando et al. 936 ) D Senna angulata (Vogel) H.S. Irwin & Barneby fruits E Senna multijuga (Rich.) H.S. Irwin & Barneby mature individual ( Lima 408 ) F Senna pendula (Humb.& Bonpl. ex Willd.) H.S. Irwin & Barneby flower ( Lima et al. 435 ) G Senna spectabilis (DC.) H.S. Irwin & Barneby flower (unvouchered) H Senna rugosa (G. Don) H.S. Irwin & Barneby leaf with extrafloral nectaries between leaflets ( Lima et al. 538 ). Photo credits A, B, E, F, H A Lima C JG Rando D F Logan G RT Queiroz https://rubens-plantasdobrasil.blogspot.com/. Figure 33. Distribution of Senna based on quality-controlled digitised herbarium records. See Suppl. material 1 for the source of occurrence data. Ecology. Senna occurs in a wide range of habitats, including wet forests, seasonally deciduous forests, seasonally semi-deciduous forests, savannas, deserts and also anthropised areas ( Irwin and Barneby 1982 ). Human uses. Species of Senna are used in traditional and conventional medicine, as bee forage for honey, ornamentals and for timber. Seeds are roasted and ground as a coffee substitute ( Miller 1754 ; Lewis 2005a ). Etymology. The name Senna derives from the Arabic "sana" or "sanna" which refers to plants with cathartic properties ( Miller 1754 ; Lewis 2005a ). Notes. Senna is morphologically characterised by the paripinnate leaves, extrafloral nectaries present in many species (on leaves, stipules, bracts, and sepals; leaf nectaries with convex secretory surface, the others are embedded and externally not clearly visible), yellow petals, heteromorphic androecium usually with 6-7 fertile stamens (Fig. 22 ), indehiscent or dehiscent fruits, and valves not twisted after dehiscence. Irwin and Barneby (1982) recognised an infrageneric classification with six sections and 35 series within Senna . In the following years, new taxonomic revisions of Senna for Australia ( Randell 1988 , 1989 , 1990 ) and Asia ( Singh 2001 ) recognised new taxa, including three new series, totalling 38 series within Senna . Phylogenetic studies based on morphological and molecular data corroborated the monophyly of Senna ( Bruneau et al. 2001 ; Herendeen et al. 2003a ; Marazzi et al. 2006 ) although five of the six sections and part of the 38 series were not resolved as monophyletic ( Marazzi et al. 2006 ). The only monophyletic section, Senna sect. Psilorhegma (Vogel) H.S. Irwin & Barneby, comprises species characterised by having all stamens fertile (i.e., a synapomorphy of this clade). Phylogenies have consistently retrieved seven strongly supported clades supported by floral morphological features and presence or absence of extrafloral nectaries ( Marazzi et al. 2006 ; Marazzi and Sanderson 2010 ). Species of the clade sister to the rest of the genus are characterised by symmetrically bilateral flowers, as also found in one of the more derived clades, in which monosymmetry evolved secondarily, with all other clades characterised by variably weakly or strongly asymmetric (enantiostylous) flowers ( Marazzi and Endress 2008 ). Senna is outstanding within legumes with respect to its specialisation in pollination mode. This specialisation is expressed especially in the androecium in which the diversity pertains to patterns of heteranthery and anther elaborations, including dehiscence patterns, pointing direction of the pores, and extension of the lateral furrow ( Marazzi et al. 2007 ). Indeed, it can be regarded as the genus with the greatest androecial diversity among Cassieae . Although extrafloral nectaries are absent in two clades of the tribe, recently described stipular nectaries with the secretory tissue embedded within the tissue are a synapomorphy for another clade ( Marazzi et al. 2013 ), and all other species, which are grouped together in a clade, have the well-known specialised leaf nectaries. Molecular dating analyses ( Marazzi and Sanderson 2010 ) indicate that Senna originated in the early Eocene and the lineages with specialised extrafloral nectaries evolved in the late Eocene, after the main radiation of ants. These extrafloral nectaries represent a relatively old key innovation in Senna , in which the association with ants provides protection to the plants, and may have promoted the colonisation of new habitats appearing with the early uplift of the Andes ( Marazzi et al. 2006 , 2013 ; Marazzi and Sanderson 2010 ). Taxonomic references. Bortoluzzi et al. (2020) ; Du Puy 1995; Irwin and Barneby (1982) ; Lima et al. (2023) ; Lock (1988) ; Miller (1754) ; Queiroz (2009) ; Randell (1988 , 1989 , 1990 ); Randell and Barlow (1998) ; Singh (2001) .