Finding the elusive floral synapomorphies for the disparate, yet closely related, families Actinidiaceae, Roridulaceae, and Sarraceniaceae (Ericales)

Stefan Löfstrand, Jürg Schönenberger

The sarracenioid clade (Actinidiaceae, Roridulaceae, Sarraceniaceae), together with the ericoid clade (Clethraceae, Cyrillaceae, Ericaceae), form the so-called core Ericales, a clade that has been well supported by various molecular phylogenetic studies. In pre-molecular classifications the sarracenioid families were often neither affiliated with other ericalean taxa, nor considered closely related with each other. The reason for this is that they differ conspicuously in their habit, way of nutrient uptake and/or superficial floral structure. At a glance, the members of the sarracenioid clade indeed share few features: Actinidiaceae are trees and lianas with extensive plasticity in sexual system, flower size, and number of floral organs; Roridulaceae are small protocarnivorous shrubs with simple, pentamerous flowers; and Sarraceniaceae are insectivorous herbs with highly specialized flowers in two genera, whereas the third genus has apparently simpler flowers with an equivocal origin of the perianth organs. We conducted a detailed comparative study of floral morphology, anatomy, and histology and in order to infer the ancestral states of key floral morphological features in the sarracenioids, we reconstructed the evolution of selected floral traits based on a molecular phylogeny. Special attention is given to patterns and processes of anther inversion among the sarracenoid families. We also discuss two Cretaceous floral fossils that have earlier been assigned to Actinidiaceae. The sarracenioids share a series of general and – at the level of the Ericales – apparently plesiomorphic floral features including pentamery, actinomorphy and hypogyny; other, more specialised features such as the number of stamens, petal union, and integument number are homoplasious within the clade. An interesting floral feature shared by the sarracenioids is late anther inversion, which in Ericales is restricted to the ericoids and sarracenioids. Potential floral synapomorphies for the sarracenioids include proximally thick petals and ovules with a nucellar hypostase. For the subclade of Actinidiaceae and Roridulaceae, potential synapomorphies include the presence of raphides and mucilage cells in floral tissue, a secretory inner surface in the gynoecium and the absence of synlateral vasculature in the ovary. In core Ericales, there is a strong correlation between structurally ventrifixed anthers and inversion from extrorse to introrse anther orientation during flower development.

Department für Botanik und Biodiversitätsforschung
ÖFOS 2012
106042 Systematische Botanik, 106008 Botanik, 106012 Evolutionsforschung
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