Floral ontogeny in Dipterygeae (Fabaceae) reveals new insights into one of the earliest branching tribes in papilionoid legumes

Abstract

Flowers of Dipterygeae (Fabaceae, Papilionoideae) exhibit an unusual petaloid calyx. The two adaxial sepals are large and petaloid, and the three abaxial sepals form a three-toothed lobe. The goal of this study was to elucidate the ontogenetic pathways of this peculiar calyx in light of the floral development of the three genera that comprise the tribe. Floral buds of Dipteryx alata, Pterodon pubescens and Taralea oppositifolia were analysed using scanning electron microscopy and light microscopy. The order of bracteole and sepal initiation varies among the species. The androecium is asymmetric. The carpel cleft is positioned to the right or to the left, and is opposite the adaxial antepetalous stamen. The peculiarity of the calyx becomes noticeable in the intermediate stages of floral development. It results from the differential growth of the sepal primordia, in which the abaxial and lateral primordia remain diminutive during floral development, compared with the adaxial ones that enlarge and elongate. Bracteoles, abaxial sepals, petals and anthers are appendiculate, except in T. oppositifolia, in which the appendices were not found in bracteoles or anthers. These appendices comprise secretory canals or cavities. Considering that the ontogenetic pathway for the formation of the petaloid calyx is similar and exclusive for Dipterygeae, it might be a potential synapomorphy for the group, with the presence of secretory canals in the appendices of abaxial and lateral sepals and petals.

Beyond pollination: diversity of secretory structures during flower development in different legume lineages

“…The structure of the secretory floral cavity of Hymenaea courbaril is similar to that observed in other Leguminosae (see Teixeira & Rocha 2009;Rodrigues et al 2011a, b;Leite et al 2014) and is characterized by the presence of a uniseriate secretory epithelium surrounded by a parenchyma sheath. The shape of the epithelium cells can vary from rectangular to papillose or trabeculate cells in legume species.…”

“…The shape of the epithelium cells can vary from rectangular to papillose or trabeculate cells in legume species. The rectangular and papillose epithelial cells are the most commonly found (present study, Teixeira & Rocha 2009;Rodrigues et al 2011a, b;Leite et al 2014) whereas the trabeculate epithelial cells seems to be restricted to the Papilionoideae clade (see Turner 1986;Teixeira et al 2000;Teixeira & Rocha 2009). No functions have been associated to the shape of epithelial cells until now.…”

“…2) which contain species of the traditional subfamily Caesalpinioideae, such as Hymenaea courbaril (present study), H. stigonocarpa (Paiva & Machado 2004;Paiva & Oliveira 2004), Copaifera langsdorfii (Pedersoli et al 2010;Rodrigues et al 2011a, b) and C. trapezifolia (Milani et al 2012). There are many such reports also in the Papilionoideae clade, as in the Dipterygeae (Leite et al 2014), Amorpheae and Psoraleeae (Turner 1986) tribes, and in the genera Lonchocarpus (Teixeira et al 2000), Dalhstedtia (Teixeira & Rocha 2009), Myrocarpus, Myroxylon, Myrospermum (Sartori & Tozzi 2002 and Poiretia (Müller 1984). However, few reports are available about the cavities and/or ducts in the flowers of the family.…”

“…However, few reports are available about the cavities and/or ducts in the flowers of the family. In addition to H. courbaril, these structures have been described in the perianth of two species of Dahlstedtia (Teixeira & Rocha 2009;, and in the perianth of Copaifera langsdorfii (Pedersoli et al 2010), Pterodon pubescens, Dipteryx alata and Taralea oppositifolia (Papilionoideae clade) (Leite et al 2014), and in the ovary of Hymenaea stigonocarpa (Paiva & Oliveira 2004).…”

“…Studies of this nature are concentrated on nectaries (Bernadello 2007) and osmophores (Mansano & Teixeira 2008;Marinho et al 2014), secretory structures related to pollination, while other types such as secretory trichomes, idioblasts, cavities and ducts have been less explored in this family comprising such a wealth of species. The few examples available include studies of secretory trichomes in the floral parts of Bauhinia (Tucker 1984, Marinho et al 2016 and Chamaecrista dentata (Meira et al 2014), in the perianth of Indigofera (Kumar et al 1986, Marquiafável et al 2009, in the sepals of Dahlstedtia , in the ovary of Glycine (Healy et al 2009), and in the bracteoles of Mimosa (Leelavathi et al 1984); studies of the colleters in the bracts of Holocalyx balansae and Zollernia ilicifolia (Mansano & Teixeira 2008) and Hymenaea stignocarpa (Paiva & Machado 2006); of the secretory idioblasts in the perianth of Caesalpinia echinata (Teixeira & Machado 2007) and in the ovary of Swartzia langsdorffii (Colpas & Oliveira 2002); and studies of the secretory cavities in the perianth of Dahlstedtia (Teixeira & Rocha 2009, in the ovary of Hymenaea stigonocarpa (Paiva & Oliveira 2004), and of the secretory ducts and cavities in the petals and sepals of Pterodon pubescens, Dipteryx alata and Taralea oppositifolia (Leite et al 2014).…”