Tanaecium

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 : 189-190

X. Tanaecium clade

TAXONOMIC INFORMATION. — This clade contains a single genus, Tanaecium , with four phloem wedges in transversal section and a single species, Tanaecium tetramerum (A.H.Gentry) Zuntini & L.G.Lohmann , that lacks phloem wedges and only shows a regular phloem. Tanaecium currently includes species from seven previously recognized genera ( Table 1 ), Arrabidaea , Ceratophytum Pittier , Pseudocatalpa A.H.Gentry , Spathicalyx J.C.Gomes, Sphingiphila A.H.Gentry , Paragonia Bureau , and Periarrabidaea A.Samp.

TOTAL NUMBER OF SPECIES IN THIS CLADE. — 21 species ( Frazão & Lohmann 2019).

STUDIED SPECIES. — Three species, Tanaecium bilabiatum (Sprague) L.G.Lohmann , T. pyramidatum (Rich.) L.G.Lohmann , and T. tetramerum (A.H. Gentry) Zuntini & L.G.Lohmann.

Regular phloem

Thin to thick fiber bands, assemblages generally present ( Fig. 13A ), but absent in T. tetramerum . Exclusively thin fiber bands occur in Tanaecium bilabiatum and T. tetramerum ( Fig. 13D ).

Variant phloem

General configuration. Semi-fibrous ( Fig. 13B, C ) to fibrous, with semi-fibrous species ( Tanaecium pyramidatum ) exhibiting fiber bands alternating with 4-8 rows of sieve elements and phloem parenchyma ( Fig. 13B, C ), and fibrous species ( Tanaecium bilabiatum ) showing a matrix of fibers that intermingle all other cells. The axial elements exhibit a diffuse to tangential arrangement ( Fig. 13B, C ).

Sieve-tube elements. As seen in transversal section, each sieve element is associated with 1-2 companion cells ( Fig. 13C ). The sieve elements are generally solitary or in multiples of 2-3 cells ( Fig. 13C ). As seen in tangential section, the sieve elements are short (<1 mm) and their end walls are inclined, bearing compound sieve plates with 16-18 sieve areas.

Axial parenchyma. The phloem parenchyma is sieve-tube-centric incomplete. In Tanaecium pyramidatum , the phloem parenchyma is much more abundant, also forming radial rows ( Fig. 13B, C ) that may be lignified in some portions ( Fig. 13B, C ), completely lignified in the nonconducting phloem. In T. bilabiatum , incomplete tangential rows may be found near the sieve elements.

Fibers. In T. pyramidatum the fiber band has 1-2 rows of cells ( Fig. 13B, C ), while in T. bilabiatum the fibers form a matrix that intermingle all other cells.

Rays. The limiting rays are lignified to both xylem and phloem faces, with a radial row non-lignified between them. The wedge rays have randomly alternating portions lignified and non-lignified ( Fig. 13B ).

Crystals. Absent.

Periderm

A single periderm is formed. The phellem is stratified in Tanaecium pyramidatum and T. tetramerum , non-stratified and thin-walled in T. bilabiatum ( Table 2 ). The phelloderm is thick, with over three layers of cells, non-stratified. Lenticels were only observed in T. pyramidatum , non-stratified, with lignified filling cells ( Table 2 ).

Figures

FIG. 13. — Secondary phloem of Tanaecium and Callichlamys: A-E, transverse sections: A-C, Tanaecium pyramidatum; A, regular phloem. Tiny sieve tubes (arrows) mostly in assemblages with parenchyma cells. Thin fiber band of up to 3 cells; B, variant phloem to the same scale as the previous photo. Semi-fibrous phloem. Note sieve tubes (arrows) much wider. Rays lignified or not in random portions; C, detail of the variant phloem. Sieve tubes (*) with one to two companion cells (yellow arrows) lying in the same corner of the sieve tube. Sieve-tube-centric axial parenchyma; D, Tanaecium tetramerum, thin fiber bands. Sieve tubes with one companion cell each (insert); E, F, Callichlamys latifolia; E, variant phloem. Sieve tubes (arrows) solitary or in short multiples. Non-fibrous phloem. Fiber bands thin; F, longitudinal tangential section. Sieve tubes (arrows) with inclined, compound sieve plates. Rays uni- to biseriate. Scale bars: A-C 100 μm; D-F, 200 μm; insert, 25 μm.