XIII. Amphilophium clade

TAXONOMIC INFORMATION. — This clade contains a single genus, Amphilophium, with multiples of four phloem wedges in transversal section. Amphilophium currently includes species from six previously recognized genera (see Fischer et al. 2004; Table 1), Amphilophium, Distictella Kuntze, Distictis Mart. ex Meisn, Glaziova Bureau, Haplolophium Cham., and Pithecoctenium Mart. ex Meisn.

TOTAL NUMBER OF SPECIES IN THIS CLADE. — 47 species (Lohmann & Taylor 2014).

STUDIED SPECIES. — Seven species, Amphilophium bracteatum (Cham.) L.G.Lohmann, A. crucigerum (L.) L.G.Lohmann, A. dolichoides (Cham.) L.G. Lohmann, A. elongatum (Vahl.) L.G. Lohmann, A. magnoliifolium (Kunth) L.G. Lohmann, A. paniculatum (L.) Kunth, and A. pulverulentum (Sandwith) L.G. Lohmann.

Regular phloem

Thin to thick fiber bands (Fig. 15D), assemblages absent.

Variant phloem

General configuration. Non-fibrous(Fig.15C),with 20-30 rows of sieve tubes and phloem parenchyma cells between fiber bands (Fig. 15C). The axial elements tend to be diffuse, sometimes forming short radial and tangential groups (Fig.15C, F).As seen in tangential section, the axial parenchyma is storied (Fig.15G).

Sieve-tube elements. As seen in transverse section, each sieve element is associated with one companion cell (Fig. 15F). The sieve tubes are generally solitary or in multiples of two, showing no distinct arrangement (Fig. 15F), often scattered among the phloem parenchyma cells or forming radial or tangential rows of two or three cells (Fig. 15F). In A. crucigerum and A. elongatum sieve tubes of two distinct diameters are present (Fig.15F). In A. crucigerum the large and narrow sieve elements occur adjacent to one another in the phloem (Fig.15F), while in A. elongatum they are organized radially from wide (70 µm in average) to narrow (35 µm in average), gradually decreasing in diameter. As seen in longitudinal section, the sieve elements are rather short (<1 mm) and their end walls are transverse to inclined, with most sieve elements bearing simple sieve plates(Fig.15E). Compound sieve plates with 2-3 sieve areas are sometimes encountered.

Axial parenchyma. The phloem parenchyma tends to intermingle all the cells (Fig. 15F), although at some portions they can be recognized as forming radial rows of 3-4 cells (Fig.15F).Crystalliferous parenchyma surrounds the fiber bands (Fig.15E), except for A. magnoliifolium and A. pulverulentum where parenchyma cells surround the fiber bands, but crystals are lacking.

Fibers. Fiber bands occur at considerable distances (more than 20 cells) from one another in Amphilophium (Fig. 15C), the Bignonieae genus with the most distant fiber bands. The fiber bands possess 2-3 rows of cells and are discontinuous between two limiting rays, i.e., they never occupy the entire space between two rays (Fig. 15C).

Rays. The limiting rays are only lignified to the xylem face (Fig. 15C). The wedge rays are non-lignified, not even when crossing the fiber bands.

Crystals. The crystalliferous parenchyma bears styloid crystals in Amphilophium elongatum, prismatic crystals in A. crucigerum (Fig. 15E), and A. paniculatum; crystals are lacking in A. magnoliifolium . Most, if not all of the axial and ray parenchyma cells contain acicular and navicular crystals.

Periderm

A single periderm is formed (Fig. 15A). The phellem is non-stratified, with evenly thin-walled cells in Amphilophium elongatum, A. magnoliifolium, and A. paniculatum; stratified, with alternating thin and thick-walled cells in A. crucigerum (Fig. 15A, B). Prismatic crystals are found in the phellem of Amphilophium crucigerum (Fig. 15B). The phelloderm is thin in Amphilophium elongatum and thick in A. crucigerum and A. magnoliifolium, with more than three cell layers (Table 1). Stratified lenticels are found in Amphilophium crucigerum .