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SAJB-00958; No of Pages 9 South African Journal of Botany xxx (2013) xxx–xxx Contents lists available at SciVerse ScienceDirect South African Journal of Botany journal homepage: www.elsevier.com/locate/sajb Flower development in Abrus precatorius (Leguminosae: Papilionoideae: Abreae) and a review of androecial characters in Papilionoideae G. Prenner ⁎ Royal Botanic Gardens, Kew, Jodrell Laboratory, Richmond, Kew, TW9 3DS, UK article info abstract Available online xxxx The jequirity bean (Abrus precatorius) is well known because of its shiny black and red coloured seeds and be- cause of the poison (abrin) it contains. The genus Abrus is placed in a monogeneric tribe Abreae which is placed Edited by B-E Van Wyk in a relatively isolated systematic position at the base of Millettieae. To contribute to a better understanding of this taxon, a detailed ontogenetic and morphologic analysis of its flowers is presented. Floral primordia are Keywords: subtended by an abaxial bract and preceded by two lateral bracteoles which are formed in short succession. Abreae Sepal formation is unidirectional starting abaxially. All petals are formed simultaneously. The carpel is formed Abrus precatorius Androecium concomitantly with the outer (antesepalous) stamen whorl, which arises unidirectionally, starting in an abaxial fi Flower position. In the inner, antepetalous stamen whorl two abaxial stamens are formed rst, followed by two lateral Leguminosae stamen primordia. The adaxial, antepetalous position remains organ free (i.e. this stamen is lost). Later in devel- Ontogeny opment the nine stamen filaments fuse to form an adaxially open sheath. The filament bases of the two adaxial outer-whorl stamens grow inwards, possibly to provide stability and to compensate for the lost stamen. In the mature flower a basal outgrowth can be found in the position of the lost stamen. However this is more likely to be an outgrowth of the filament sheath rather than a remnant of the lost stamen. These ontogenetic patterns match in parts those found in other Millettieae (unidirectional formation of sepals and stamens, simul- taneous petal formation). In contrast, the complete loss of a stamen is rather unusual and supports the isolated position of Abreae and probably justifies (among other characters) its tribal status. A review of androecial char- acters shows that androecial merosity is on the one hand extremely variable among Leguminosae, varying from asinglestamenperflower to more than 500. On the other hand it is noteworthy that the number of stamens becomes stabilised in more derived Papilionoideae such as the large non-protein-amino-acid-accumulating clade (NPAAA clade). This indicates that the androecium has played an important role in the success of a major part of Leguminosae. © 2013 SAAB. Published by Elsevier B.V. All rights reserved. 1. Introduction tract due to their hard shell (see also Van Wyk et al., 2002; Botha and Penrith, 2008). The genus Abrus Adans. consists of ca 17 species found in Africa, For a long time the systematic position of the genus Abrus was Madagascar, India and Indo-China (Schrire, 2005). Among them, uncertain and its tribal placement problematic (see Polhill, 1981). In the jequirity bean (Abrus precatorius L.) is probably the best and more recent molecular studies the genus is consistently placed near widest known species. It is a weed found throughout the tropics and the base of a clade comprising the core Millettieae sensu Hu et al. neotropics. Some of its many common names such as Bead Vine, (2000, 2002) and various elements excluded from Phaseoleae sensu Black-Eyed Susan or Coral Bead Plant point to the use of its hard, lato (see Wojciechowski et al., 2004; Schrire, 2005). Schrire (2005) ar- shiny black and red seeds for stringing into necklaces and rosaries in gues for the maintenance of the monogeneric tribe Abreae because of India and other tropical countries. The seeds are also well known be- its basal branching position together with the unusual combination of cause of their highly poisonous protein abrin, a plant lectin, related to paripinnate leaves, nine stamens and a chemical profile of tryptophan- ricin, which inhibits cellular protein synthesis (Nelson et al., 2007). derived and pyridine-based alkaloids. Jang et al. (2010) report that even though abrin has an estimated fatal The androecium and the inflorescence are among the most inter- dose of 0.1–1 μg/kg, most cases of Abrus seed ingestions are without esting morpho-anatomical features of the genus. The androecium con- clinical findings, because the seeds pass through the gastrointestinal sists of only nine stamens whereas in most other papilionoid legumes, ten stamens in two whorls of five are found. In legumes both organ sup- ⁎ Tel.: +44 20 8332 5316; fax: +44 20 8332 5310. pression and organ loss occur (e.g. Tucker, 1988a, 1990; Prenner, 2004a; E-mail address: [email protected]. Prenner and Klitgaard, 2008). Therefore it is important to determine 0254-6299/$ – see front matter © 2013 SAAB. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.sajb.2013.06.008 Please cite this article as: Prenner, G., Flower development in Abrus precatorius (Leguminosae: Papilionoideae: Abreae) and a review of androecial characters in Papilionoideae, South African Journal of Botany (2013), http://dx.doi.org/10.1016/j.sajb.2013.06.008 2 G. Prenner / South African Journal of Botany xxx (2013) xxx–xxx whether the tenth stamen is completely lost (i.e. a stamen primordium by the two lateral primordia (Fig. 1J–K). The adaxial stamen position is no longer formed) or whether it is initiated but then suppressed early. remains organ free (Figs. 1L, 2A–C). The Abrus inflorescence is another remarkable feature which was briefly described by Tucker (1987b). It was recently studied in more 3.2. Later floral development (Figs. 2–4) detail by Prenner (in press) who showed that the axis of partial inflo- rescences of A. precatorius is reduced to a nodose structure. Further- While sepal growth is quick (see above), petal development is dis- more the meristem of partial inflorescences is relocated towards tinctly delayed and the antesepalous stamens and the carpel in the the main inflorescence axis and individual flowers are formed in a centre of the flower soon become bigger than the petals (Fig. 1L). peculiar pendulum pattern. Each flower is subtended by a bract and The petals remain smaller than the antesepalous stamens and the all flowers are formed in a basipetal continuum. Because of this, carpel until later in development (Fig. 2A, B, E). The characteristic Prenner (in press) argued that the inflorescence in A. precatorius is a papilionoid corolla which consists of an adaxial vexillum (or standard compound raceme rather than a pseudoraceme sensu Tucker (1987b). petal), two lateral wing petals and two abaxial keel petals differenti- Based on a detailed analysis of the floral development the present ates only very late in ontogeny (Fig. 3A, C). study aims to answer the following questions: (1) What is the gener- The inner, antepetalous stamen whorl also lags behind the outer al pattern of organ formation in A. precatorius? (2) Is the adaxial stamen whorl (Fig. 2B) and the stamens in this whorl are still small antepetalous (i.e. inner whorl) stamen reduced (i.e. initiated but and undifferentiated when anther formation is already well advanced not further developed) or is it completely lost (i.e. no initial in the outer whorl (Fig. 2B). Eventually anthers are also formed in the formed)? (3) How do the present findings relate to existing ontoge- inner whorl and the filaments of both whorls fuse to form an adaxially netic data in Millettieae (Teixeira et al., 2009; Naghiloo and Dadpour, open filament sheath (Figs. 2G, 3D). Early in development the filament 2010) and in other papilionoid legumes? (4) How do the results bases of the two adaxial antesepalous stamens begin to grow inwards relate to recent molecular phylogenetic hypotheses? Taking the in- towards the position of the tenth stamen which is missing (Fig. 2C–G). teresting structure of the androecium of A. precatorius as a starting The carpel develops quickly and its growth rate is about the same point, I finally present a brief review of androecial characters in or somewhat faster than that of the outer stamen whorl (Fig. 2A). The Papilionoideae. adaxial carpel cleft soon closes and hairs are starting to form on the abaxial side. Formation of the stigma sets in fairly early when the carpel 2. Material and methods begins to bend in the adaxial direction (Fig. 2D–E). Later on, the carpel is covered with a dense indumentum (Figs. 2D–H, 3A, D) and within the Inflorescences of various sizes and ages of A. precatorius were carpel four ovules are formed (Fig. 2H–I). In the androecium the adaxial collected at the Botanic Garden Graz (Teppner H., s.n., Karl Franzens position remains organ-free (Fig. 2A–G) and only in mature flowers can University Graz, Austria) and immediately fixed in 70% ethanol. For a meristematic outgrowth be found in this position (Fig. 3A, B, D–H). scanning electron microscopy (SEM) the material was dissected in Mature anthers are monomorphic and basifixed with stomata on 70% ethanol, dehydrated to 100% ethanol and critical point dried their connectives (Fig. 4A–B). The papillate stigma is surrounded by using an Autosamdri-815B critical-point dryer. The dried material hairs (Fig. 4C). Pollen is tricolporate with a coarsely reticulate tectum was mounted onto aluminium stubs with clear nail polish and coated which becomes finer towards the poles and towards the margins of with platinum in an Emitech K550a sputter coater. SEM images were the colpi (Fig. 4D–F). taken with a Hitachi S-4700-II cold field emission SEM.

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