Perianthomega

Pace, Marcelo R., Marcati, Carmen R., Lohmann, Lúcia G. & Angyalossy, Veronica, 2023, Bark anatomy of lianescent Bignoniaceae: a generic synopsis, Adansonia (3) 45 (12), pp. 167-210 : 179

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 ).

Figures

FIG. 3. — Stem cross-sections illustrating the diversity of stem architectures in Bignoniaceae lianas:A, Campsis radicans, transverse section (TS). Phloem wedges absent. Intraxylary secondary phloem and xylem present, note center of the pith totally occupied in the insert, giving a dumbbell shape to the pith; B, Pandorea jasminoides, TS, irregular, wavy cambium, forming irregular shallow arcs; C, Podranea ricasoliana, TS, irregular, wavy cambium. Insert: narrow waves of the cambium; D, Perianthomega vellozoi, TS, Type 1, four wide phloem arcs;E, Tynanthus cognatus, TS, Type 2, four phloem wedges;F, Adenocalymma nodosum, TS, Type 3, four phloem arcs, variant cambium without anticlinal divisions; G, Mansoa onohualcoides, TS, Type 4, multiple of four phloem wedges; H, Dolichandra unguis­cati, TS, Type 5, multiple dissected phloem wedges; I, Amphilophium crucigerum, TS, Type 6, included phloem wedges. Scale bars: 0.5 cm. Scale bars in inserts: 2 mm.

FIG. 7. — Secondary phloem of Perianthomega vellozoi: A, regular phloem, transverse section (TS). Stratified phloem, with thin to thick fiber bands, interrupted only by rays, and alternating with axial parenchyma and sieve tubes. Rays not lignified, not even when crossing the fiber bands; B, Variant phloem, TS, nonfibrous, stratified phloem, with mostly thick fiber bands, interrupted only by rays, and alternating with axial parenchyma and sieve tubes. Rays not lignified, not even when crossing the fiber bands; C, detail of the secondary phloem,TS, Sieve tubes solitary or in multiples of two-three, with one companion cell lying on the corner. Crystalliferous parenchyma with acicular crystals around the fibers. Acicular crystals also present in other axial and ray parenchyma cells. When sieve tubes touch a ray,their companion cells stay next to the ray;D, portion of the cambium showing a storying tendency for the fusiform initials,longitudinal tangential section (LS). Part of the developing xylem showing two maturing sieve tube elements (*), and the developing xylem, with some cells with pits already;E, secondary phloem, LS, sieve tubes smaller than 500 μm (arrows). P-protein accumulated in their sieve plates. Rays very tall, higher than 1 mm. Storied tendency not lost; F, periderm, TS, phellogen (arrow) produces a thin phelloderm and evenly thin walled phellem cells. Abbreviations: se, sieve element; cp, crystalliferous parenchyma; cz, cambial zone; dp, developing phloem; dx, developing xylem; p, axial parenchyma; pd, periderm; pl, phellem; r, rays. Scale bars: A, B, E, 200 μm; C, 50 μm; D, 150 μm; F, 100 μm.