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Abstract
The family Rapateaceae represents an early-divergent lineage of Poales with biotically pollinated showy flowers. We investigate developmental morphology and anatomy in all three subfamilies and five tribes of Rapateaceae to distinguish between contrasting hypotheses on spikelet morphology and to address questions on the presence of nectaries and gynoecium structure. We support an interpretation of the partial inflorescence (commonly termed spikelet), as a uniaxial system composed of a terminal flower and numerous empty phyllomes. A terminal flower in an inflorescence unit is an autapomorphic feature of Rapateaceae. The gynoecium consists of synascidiate, symplicate, and usually asymplicate zones, with gynoecium formation encompassing congenital and often also postgenital fusions between carpels. Species of Rapateaceae differ in the relative lengths of the gynoecial zones, the presence or absence of postgenital fusion between the carpels and placentation in the ascidiate or plicate carpel zones. In contrast with previous reports, septal nectaries are lacking in all species. The bird-pollinated tribe Schoenocephalieae is characterized by congenital syncarpy; it displays an unusual type of gynoecial (non-septal) nectary represented by a secretory epidermis at the gynoecium base.
Highlights
Molecular phylogenetic analyses have resulted in expansion of the order Poales to include more than a third of all monocot species (Bouchenak-Khelladi et al, 2014; Hochbach et al, 2018)
We report some aspects of floral development for Rapatea paludosa and Spathanthus unilateralis (Rapateoideae), Monotrema aemulans and Potarophytum riparium (Monotremoideae), and Stegolepis cardonae (Saxofridericioideae–Stegolepideae)
The occurrence of a terminal flower in an inflorescence unit is an autapomorphic feature of Rapateaceae
Summary
Molecular phylogenetic analyses have resulted in expansion of the order Poales to include more than a third of all monocot species (Bouchenak-Khelladi et al, 2014; Hochbach et al, 2018). Despite phylogenetic data on Poales from multiple sources, including different genomic markers, transcriptomes, and plastomes (e.g., Bouchenak-Khelladi et al, 2014; Barrett et al, 2016; McKain et al, 2016; Givnish et al, 2018; Hochbach et al, 2018), the precise relationships of some families that lie on very short branches remain problematic. The most detailed sampling to date involved ndhF sequence data (Givnish et al, 2000, 2004), underlining the need for more analyses with greater taxon sampling
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