Pleonotoma
Creators: name: Pace, Marcelo R.
name: Marcati, Carmen R.
name: Lohmann, Lúcia G.
name: Angyalossy, Veronica
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Lamiales
Bignoniaceae
Pleonotoma

description: IV. Pleonotoma clade
TAXONOMIC INFORMATION. — This clade contains a single genus, Pleonotoma, with four phloem wedges in transversal section.
TOTAL NUMBER OF SPECIES IN THIS CLADE. — 16 species (Lohmann & Taylor 2014; Gomes et al. 2020).
STUDIED SPECIES. — Five species, Pleonotoma dendrotricha Sandwith, P. melioides (S.Moore) A.H.Gentry, P. orientalis Sandwith, P. tetraquetra (Cham.) Bureau, and P. stichadenia K.Schum.
Regular phloem
Fibers are absent, with sclereids found otherwise (Fig. 9A). Sclereids are arranged in clusters, differentiating close to the cambial zone (Fig. 9A, C). Because these sclereids have tapering ends, they are considered fibersclereids (Fig. 9C). Assemblages present (Fig. 9B arrowhead).
Variant phloem
General configuration. Fibrous (Fig. 9D) to semi-fibrous (Fig. 9E), typically with one tangential row of sieve tubes surrounded by phloem parenchyma and fibers (Fig. 9E), presenting, therefore, a tangential arrangement (Fig. 9E).
Sieve-tube elements. As seen in transverse section, each sieve element is associated with 1-3 companion cells (Fig. 9E, F). The sieve elements are generally in multiples of two, ranging from solitary to multiples of 4-5 in a tangential arrangement (Fig. 9E), sometimes in clusters. Sieve elements of two distinct diameters can be found adjacent to each other (Fig. 9E). Sieve elements of narrower radial diameter can be, moreover, found associated with a parenchyma band.As seen in longitudinal section, the sieve elements are long (> 1 mm) and their end walls are inclined, bearing sieve plates with more than 30 sieve areas.
Axial parenchyma. The phloem parenchyma is sieve-tube-centric to sieve-tube-centric incomplete (Fig. 9E, F). A parenchyma band of 3-4 rows of cells is associated with narrower sieve elements.In addition, radial rows of phloem parenchyma cells are often present, sometimes lignified (Fig. 9E).
Fibers. Present as either fiber bands of 2-3 rows of cells (Fig. 9E) or as the fibers constituting the ground tissue where all other cells are embedded (Fig. 9D).
Rays. The limiting rays are lignified only to the xylem face (Fig. 9E). The wedge rays are non-lignified, even when crossing the fiber bands (Fig. 9E, F).
Crystals. Prismatic crystals are abundant, both in the phloem and ray parenchyma (Fig. 9F), and even more common in the ray cells. The number of crystals per cells is variable, ranging from a single crystal per cell that occupies almost the entire cell lumen, to many (c. eight), but much smaller crystals per cell (Fig. 9F).
Periderm
A single periderm formed. The phellem is stratified, composed of thin and thick-walled cells in alternation. The phelloderm is thick, with over three cell layers, non-stratified (Table 2).
description: Published as part of Pace, Marcelo R., Marcati, Carmen R., Lohmann, Lúcia G. & Angyalossy, Veronica, 2023, Bark anatomy of lianescent Bignoniaceae: a generic synopsis, pp. 167-210 in Adansonia (3) (3) 45 (12) on page 182, DOI: 10.5252/adansonia2023v45a12, http://zenodo.org/record/8006364