Paepalanthus sect. Diphyomene comprises 18 species with a convoluted
taxonomic history. Aiming to correlate anatomical structures with the systematics of
this group and its relatives, we studied the anatomy of scapes, reproductive axis
bracts, and leaves of 20 Paepalanthus species. Bracts and leaves show differences in
epidermal cell thickening; mesophyll width; vascular bundle arrangement; presence or
absence of a hypodermis; types of cells in the vascular bundle sheath extensions;
margin shape and composition; and presence or absence of aquiferous parenchyma.
Scapes differ in contour, rib number, and pith size. Some diagnostic characters found
are presence of aquiferous parenchyma and absence of vascular bundle sheath extensions
in leaves of P. urbanianus; vascular bundles decreasing in size towards the margin
of leaves and bracts, and scapes with a triangular contour in P. flaccidus; scapes
with nine ribs in P. acanthophyllus and ten in P. macer. All anatomical features
are summarized in tables. These results aid in the identification and characterization of
the species of P. sect. Diphyomene. They also support the current section circumscription,
reinforcing the relevance of the anatomical characters in order to define natural
groups.