I. Perianthomega clade

TAXONOMIC INFORMATION. — This clade contains a single genus, Perianthomega, with four phloem arcs in transversal section (Fig. 3D). The genus was placed previously in Tecomeae s.l. (Gentry 1992; Fischer et al. 2004; Table 1), but subsequently transferred into Bignonieae (Lohmann & Taylor 2014).

TOTAL NUMBER OF SPECIES IN THIS CLADE. — One species (Lohmann & Taylor 2014).

STUDIED SPECIES. — One species, Perianthomega vellozoi Bureau.

Regular phloem

Thin to thick fiber bands (Fig. 7A), without assemblages.

Variant phloem

General configuration. Non-fibrous, stratified, with approximately 12-18 rows of sieve tubes and phloem parenchyma cells between fiber bands (Fig. 7B). A tendency to a storied structure is evident in the cambial zone (Fig. 7D) and secondary xylem, less so in the secondary phloem (Fig. 7E).

Sieve tube elements. As seen in transverse section, each sieve element is associated with one companion cell (Fig. 7C), sometimes two, one at each opposite corner of the sieve element. Sieve tubes are solitary or radial and composed of 2-3 cells (Fig. 7B, C). As seen in longitudinal section, the sieve elements are short (<500 µm) (Fig. 7E) and their end walls are transverse to slightly inclined (Fig. 7D, E), bearing simple sieve plates (Fig. 7E).

Axial parenchyma. The phloem parenchyma forms a matrix where sieve elements and fiber bands are embedded (Fig. 7B, C). Long radial rows of phloem parenchyma, sometimes with more than 10 cells, are present. Furthermore, a crystalliferous parenchyma is found surrounding the fiber bands (Fig. 7C).

Fibers. The fiber bands are composed of 4-6 rows of cells (Fig. 7B).

Rays. Limiting rays are not present in Perianthomega . The rays are non-lignified, not even when crossing the fiber bands (Fig. 7B).

Crystals. Acicular crystals are present and more abundant in the crystalliferous parenchyma, although also found in all other cells of the phloem and ray parenchyma (Fig. 7C).

Periderm

Only one periderm is formed (Fig. 7F). The phellem is composed of evenly thin-walled cells. The phelloderm is thin, with less than three layers of cells (Fig. 7F).