II. Stizophyllum clade

TAXONOMIC INFORMATION. — This clade contains a single genus, Stizophyllum, with four phloem wedges in transversal section (Fig. 4A).

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

STUDIED SPECIES. — Three species, Stizophyllum inaequilaterum Bureau & K.Schum., S. perforatum (Cham.) Miers, and S. riparium (Kunth) Sandwith.

Regular phloem

Thick fiber bands (Fig. 8B), assemblages present (Fig. 8C).

Variant phloem

General configuration. Fibrous phloem (Fig. 8A, D), with some non-fibrous, parenchyma bands in alternation (Fig. 8A, D). Axial elements with either a tangential (Fig. 8A) or a radial arrangement (Fig. 8D).

Sieve tube elements. As seen in transverse section, each sieve element is associated with 1-3 companion cells (Fig. 8E), lying on the same corner of the sieve tube (Fig. 8E). The sieve elements are generally arranged in multiples of 2-3 in a radial or tangential disposition, sometimes in clusters (Fig. 8E). Sieve tubes of narrower radial diameter can be found associated with a parenchyma band (Fig. 8D). Such sieve tubes are found in radial multiples of 2-4 cells. As seen in longitudinal section, the sieve elements are thinner than 1 mm, with end walls inclined, bearing sieve plates with 6-10 sieve areas (Fig. 8F). Ray sieve-tube elements are common (Fig. 8F).

Axial parenchyma. The phloem parenchyma is sieve-tube-centric incomplete (Fig. 8D, E), not surrounding the entire sieve tube or sieve tube group, and commonly lignified (Fig. 8E). A parenchyma band of 3-4 rows of cells is present (Fig. 8A, D) associated with narrower sieve elements. In addition, radial rows of axial parenchyma cells are present in some places, sometimes entirely lignified

Fibers. Fibers form a matrix where all other cells can be found (Fig. 8A, D, E).

Rays. The limiting rays are lignified to both xylem and phloem sides, with a radial row of non-lignified cells between them (Fig. 8A). The wedge rays have randomly alternating portions that can be lignified or non-lignified (Fig. 8D, E).

Crystals. Acicular crystals are present in most of the phloem and ray parenchyma cells.

Periderm

Only one periderm is present. The phellem is stratified, composed of thin and thick-walled cells disposed in alternation. The phelloderm is thick, with more than three layers of cells, non-stratified (Table 2).