Elucidating the unusual floral features ofSwartzia dipetala(Fabaceae)

Abstract

In this study, we evaluated the floral ontogeny of Swartzia dipetala, which has peculiar floral features compared with other legumes, such as an entire calyx in the floral bud, a corolla with one or two petals, a dimorphic and polyandrous androecium and a bicarpellate gynoecium. We provide new information on the function of pollen in both stamen morphs and whether both carpels of a flower are able to form fruit. Floral buds, flowers and fruits were processed for observation under light, scanning and transmission electron microscopy and for quantitative analyses. The entire calyx results from the initiation, elongation and fusion of three sepal primordia. A unique petal primordium (or rarely two) is produced on the adaxial side of a ring meristem, which is formed after the initiation of the calyx. The polyandrous and dimorphic androecium also originates from the activity of the ring meristem. It produces three larger stamen primordia on the abaxial side and numerous smaller stamen primordia on the adaxial side. These two types of stamens bear morphologically similar ripening pollen grains. However, prior to the dehiscence of thecae and presentation of pollen in the anther, only the pollen grains of the larger stamens contain amyloplasts. Two carpel primordia are initiated as distinct protuberances, alternating with the larger stamens, in a slightly inner position in the floral meristem, constituting the bicarpellate gynoecium. Both carpels are able to form fruit, although only one fruit is generally produced in a flower. The increase in gynoecium merism probably results in an increase in the surface deposition of pollen grains and consequently in the chance of pollination. This is the first study to thoroughly investigate organogenesis and the ability of the carpel to form fruit in a bicarpellate flower from a member of Fabaceae, in addition to the pollen ultrastructure in the heteromorphic stamens associated with the 'division of labour' sensu Darwin.

Bicarpellate gynoecium in two species of Senna (Fabaceae, Caesalpinioidae, Cassiinae)

“…micans reinforces the hypothesis that variation in plant reproduction may be the result of selective pressures favoring reproductive success. These data corroborate the study of Paulino et al (2013), which recorded double fruit in the bicarpellate Swartzia dipetala Willd. ex Vogel.…”

“…Patterns of enantiostyly vary, and seem to enhance reproductive ability (Almeida et al 2013). Although enantiostylous fl owers with a pluricarpellate gynoecium are not common within Fabaceae, their occurrence is interpreted as a strategy to maximize pollen capture by the stigma, thereby increasing reproductive success (Prenner 2004;Endress & Doyle 2009;Paulino et al 2013).…”

Terata of two legume species with radialized corolla: some correlations in floral symmetry

“…Even in some species with normally polymerous gynoecium (e.g., some of Swartzia species), all carpels are oriented in the same way, i.e., with their clefts towards the adaxial petal (Paulino et al 2013;Sinjushin 2014). Only mimosoid flowers with whorled polymerous gynoecium can be called truly polysymmetric in all floral whorls.…”

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

“…The beauty, diversity and highly interesting construction of their flowers have been the target of many anatomy and ontogeny studies (eg. Tucker 1994;Pedersoli et al 2010;Paulino et al 2013;2014;Pedersoli & Teixeira 2016). Thus, many reports about the floral secretory structures of this family would be expected to be available, whereas this is not the case.…”