Towards unlocking the deep nodes of Leguminosae: Floral development and morphology of the enigmatic Duparquetia orchidacea (Leguminosae, Caesalpinioideae)

Abstract

Duparquetia orchidacea (Caesalpinioideae-Cassieae-Duparquetiinae) is a monotypic liana from tropical West Africa. Its highly unusual, zygomorphic flowers, the unique pollen morphology, and the lack of vestured pits in the wood correspond with previous phylogenetic studies that resolved the position of the species to an isolated position among the early-branching Leguminosae. Here we present a detailed analysis of floral morphology and development to clarify open questions of its floral organization. We provide new data that can be useful in clarifying phylogenetic relationships among early branching Leguminosae and improve our understanding of floral evolution in this large and important plant family. For comparison, we also present developmental data for other Fabales. Our analysis reveals some unusual and in parts unique developmental patterns, such as strict acropetal organ formation, loss and suppression of floral organs, and early petal enlargement. We interpret alternating left-right symmetries in floral development as clues to a spiral organ formation in ancestral taxa. Early asymmetry of the young carpel helps to interpret enantiostyly of other Leguminosae as an example of imprinted shape. Finally, we show that cochlear-descending petal aestivation in Duparquetia and in Papilionoideae is based on different ontogenetic patterns and therefore is most probably nonhomologous.

Flower development ofGoniorrhachis marginatareveals new insights into the evolution of the florally diverse detarioid legumes

“…A strikingly similar pattern was found in the early-branching Duparquetia orchidacea, which also forms only four sepals and in which the first two sepals enlarge considerably and sepals 3 and 4 are formed in short succession in transverse position (Prenner and Klitgaard, 2008). Here too, Prenner and Klitgaard (2008) concluded that there was not enough meristem left for the formation of a fifth sepal primordium.…”

“…Here too, Prenner and Klitgaard (2008) concluded that there was not enough meristem left for the formation of a fifth sepal primordium. In contrast to this similarity in the sepal whorl, petal and stamen formation varies considerably among the two species (in Duparquetia petal formation is almost simultaneous, petal aestivation is cochlear descending and there are only four stamens formed, as shown by Prenner and Klitgaard, 2008).…”

“…Here too, Prenner and Klitgaard (2008) concluded that there was not enough meristem left for the formation of a fifth sepal primordium. In contrast to this similarity in the sepal whorl, petal and stamen formation varies considerably among the two species (in Duparquetia petal formation is almost simultaneous, petal aestivation is cochlear descending and there are only four stamens formed, as shown by Prenner and Klitgaard, 2008). This shows on the one hand that there are ontogenetic patterns such as the complete loss of an organ in taxa that are not closely related, based on similar ontogenetic patterns, and on the other hand that organ formation among different organ whorls is controlled independently in the two species (i.e.…”

“…Deviations from ascending cochlear aestivation are rare in Caesalpinioideae s.l. In Duparquetia orchidacea petal aestivation is cochlear descending (Prenner and Klitgaard, 2008), which is the common pattern in Papilionoideae. However, in Papilionoideae there is some variation in petal aestivation among early-branching taxa (e.g.…”

“…remarkable new insights into the evolution of extrafloral nectaries (Marazzi et al, 2012), the polycarpellate gynoecium (Paulino et al, 2014) and the high persistence of legume-rhizobia symbiosis (Werner et al, 2015). The wealth of floral ontogenetic data available for legumes (Tucker, 1987(Tucker, , 1988a(Tucker, , b, 2003cPrenner, 2004a, b;Marazzi and Endress, 2008), including recent results for phylogenetically enigmatic lineages that branch off at deep nodes (Prenner and Klitgaard, 2008;Prenner et al, 2015), are likewise extremely useful for large-scale comparison and as sources for potential synapomorphic characters of still obscure relationships. The caesalpinioid Detarieae lineage is an example of such a highly morphologically heterogeneous collection of genera marked by an exceptional lability in floral evolution (Bruneau et al, 2014).…”