Senna Mill., Gard. Dict. Abr. (ed. 4). 1754.

Bruneau, Anne, de Queiroz, Luciano Paganucci, Ringelberg, Jens J., Borges, Leonardo M., Bortoluzzi, Roseli Lopes da Costa, Brown, Gillian K., Cardoso, Domingos B. O. S., Clark, Ruth P., Conceicao, Adilva de Souza, Cota, Matheus Martins Teixeira, Demeulenaere, Else, de Stefano, Rodrigo Duno, Ebinger, John E., Ferm, Julia, Fonseca-Cortes, Andres, Gagnon, Edeline, Grether, Rosaura, Guerra, Ethiene, Haston, Elspeth, Herendeen, Patrick S., Hernandez, Hector M., Hopkins, Helen C. F., Huamantupa-Chuquimaco, Isau, Hughes, Colin E., Ickert-Bond, Stefanie M., Iganci, Joao, Koenen, Erik J. M., Lewis, Gwilym P., de Lima, Haroldo Cavalcante, de Lima, Alexandre Gibau, Luckow, Melissa, Marazzi, Brigitte, Maslin, Bruce R., Morales, Matias, Morim, Marli Pires, Murphy, Daniel J., O'Donnell, Shawn A., Oliveira, Filipe Gomes, Oliveira, Ana Carla da Silva, Rando, Juliana Gastaldello, Ribeiro, Petala Gomes, Ribeiro, Carolina Lima, Santos, Felipe da Silva, Seigler, David S., da Silva, Guilherme Sousa, Simon, Marcelo F., Soares, Marcos Vinicius Batista & Terra, Vanessa, 2024, Advances in Legume Systematics 14. Classification of Caesalpinioideae. Part 2: Higher-level classification, PhytoKeys 240, pp. 1-552 : 1

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 ).

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).

Figures

Figure 22. Examples of variation in stamens and pistil among Cassieae genera A Cassia moschata Kunth (Rando et al. 1184) B Senna macranthera (DC. ex Collad.) H. S. Irwin & Barneby (Rando et al. 272) C Chamaecrista bahiae (H. S. Irwin) H. S. Irwin & Barneby (Rando et al. 1214) D Melanoxylum brauna Schott (Cardoso et al. 2439) E Recordoxylon speciosum (Benoist) Gazel ex Barneby (Pereira-Silva et al. 15631) F Vouacapoua americana Aubl (Nascimento 245). G Batesia floribunda Spruce ex Benth (based on photographs of Projeto Flora Reserva Ducke, INPA / DFID, comm. Mike Hopkins). Scale: 1 cm. Drawn by Najla M. B. Scheidegger / @ ilustre. nt.

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.