Abstract
The anatomy of leaves and inflorescence axes of Spathanthus (2 spp.), Rapatea (2 spp.), Cephalostemon (1 sp.), and Duckea (1 sp.) (Rapateoideae, Rapateaceae) was studied to identify useful characters for taxonomy. The cross-section shape of inflorescence axis differentiates the genera, while the cross-section shape and structure of leaf midrib has a specific value. The following characteristics are exclusive of Spathanthus: silica cells randomly distributed in the leaf epidermis; plicate chlorenchyma in the leaf blade; presence of fiber bundles in the mesophyll and in the inflorescence axis parenchyma. Spathanthus is also distinguished by the number, type and distribution of vascular bundles in the inflorescence axis. The genus Rapatea is characterized by the presence of stomata and silica cells only on the abaxial epidermis of the leaves and chlorenchyma composed of arm cells in the leaf blade. Characteristics with diagnostic value for Cephalostemon riedelianus are: leaf epidermal cells with straight to slightly sinuous walls in frontal view, inflorescence axes presenting a defined cortex, fiber bundles facing the larger vascular bundles and a fistulous pith. The anatomical characteristics of the leaves and inflorescence axes thus proved to be of taxonomic value in generic and specific levels. They are also useful to differentiate Rapateoideae from other subfamilies of Rapateaceae.
Highlights
Rapateaceae comprise approximately 100 species in 16-17 genera (Stevenson et al 1998, Givnish et al 2004) and are a basal family in Poales along with Bromeliaceae and Typhaceae (Linder and Rudall 2005, Givnish et al 2010)
Given the importance of identifying anatomical characteristics with taxonomic value, this paper aimed to describe the anatomy of leaves and inflorescence axes of Spathanthus bicolor, S. unilateralis, Rapatea paludosa, R. ulei, Cephalostemon riedelianus, and Duckea squarrosa (Rapateoideae) to characterize the subfamily and the genera, contributing to the understanding of infrafamiliar relationships
The leaves of the studied species can be characterized by the presence of a single-layered epidermis with silica cells; tetracytic stomata; a regular, plicate, or arm chlorenchyma in the mesophyll; and collateral, double-sheathed vascular bundles
Summary
Rapateaceae comprise approximately 100 species in 16-17 genera (Stevenson et al 1998, Givnish et al 2004) and are a basal family in Poales along with Bromeliaceae and Typhaceae (Linder and Rudall 2005, Givnish et al 2010). In Brazil, approximately 39 species and nine genera are found, growing primarily in the Amazon region (Monteiro 2014). They are perennial herbs with a short stem from which distichous or spirodistichous leaves and inflorescence axes (scapes) originate (Maguire 1958, Stevenson et al 1998). Spathanthus is the sister group of Rapatea and Cephalostemon (Givnish et al 2004) These three genera were the first to diverge and are remarkable for presenting dispersion ranges that extend out of the Guayana Shield to the Amazon Basin (Givnish et al 2000)
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