Characteristics of the xylem

Annual rings are absent. Characteristic is the presence of successive cambia. The more-or-less circular arranged xylem/phloem zones are separated by parenchymatic zones (conjunctive tissue) (Figs. 1-4). Perforations are simple and inter-vessel pits are small and round (Fig. 5). Fibres are thin- to thick-walled. The axial parenchyma is absent or paratracheal (Fig. 4). Rays can be fairly large with often irregularly formed cells, 1-3-seriate or absent (Figs. 2, 4 and 6). Ray cell walls are mostly thin and un-lignified (Fig. 1). Short rhaphides (20 pm) are bundled in a few idioblasts in the inter-vascular bundle zone (Fig. 3). Crystals are absent in Aizoon canariensis.

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Fig. 1. Stem with successive cambia. Irregular bands of xylem, phloem and adjacent parenchymatic cells, connected with large rays. Root collar of a 15 cm-high plant with succulent leaves, ruderal site, thermophile zone, subtropical climate. Gran Canaria, Canary Islands. Aizoon canariense, transverse section.

Fig. 3. Stem with successive cambia. Irregular bands of xylem, phloem and parenchyma bands. Grey filled cells represent id-ioblasts with bundles of rhaphides. Stem of a several-meter-long chamaephyte with succulent leaves, garden on the coast, Mediterranean zone, Algarve, Portugal. Carpobrotus acinaciformis, transverse section.

Fig. 2. Stem with successive cambia. Tangential bands of xylem, phloem and adjacent parenchymatic conjunctive tissue. Rays are absent. Root collar of a long hanging plant with succulent leaves, thermo-phile zone, subtropical climate, Gomera, Canary Islands. Aptenia cordifolia, transverse section.

Fig. 3. Stem with successive cambia. Irregular bands of xylem, phloem and parenchyma bands. Grey filled cells represent id-ioblasts with bundles of rhaphides. Stem of a several-meter-long chamaephyte with succulent leaves, garden on the coast, Mediterranean zone, Algarve, Portugal. Carpobrotus acinaciformis, transverse section.

Fig. 2. Stem with successive cambia. Tangential bands of xylem, phloem and adjacent parenchymatic conjunctive tissue. Rays are absent. Root collar of a long hanging plant with succulent leaves, thermo-phile zone, subtropical climate, Gomera, Canary Islands. Aptenia cordifolia, transverse section.

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Fig. 4. Stem with successive cambia. Tangential bands of xylem and phloem, in formation process in mid February. Phloem with small, radially oriented cells, adjacent parenchyma with large cells. Rays mostly unlignified, 1-3-seriate. Root collar of succulent, 10 cm-high plant, ruderal site, ther-mophile zone, subtropical climate, Tenerife, Canary Islands. Mesembryanthemum cristallinum, transverse section.

Fig. 5. Vessels with simple perforations and small round inter-vessel pits. Root collar of a 15 cm-high annual plant with succulent leaves, ruderal site, thermophile zone, subtropical climate, Gran Canaria, Canary Islands. Aizoon canariense, radial section.

Fig. 6. Rays 3 to 6-seriate. Cell size and form is variable. Root collar of a 15 cm-high annual plant with succulent leaves, ruderal site, thermophile zone, subtropical climate, Gran Canaria, Canary Islands. Aizoon canariense, tangential section.

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