Characteristics of the phloem and the cortex

Clade Saxífraga

The bark is not well structured. Sieve tubes and parenchyma cells normally cannot be distinguished (Fig. 14). Many species have a well-developed phellem with often square to rectangular, thick-walled cork cells. The phellem is extraordinarily thick on individuals with exposed stems, e.g. Saxifraga oppositifolia (Fig. 15). Crystals and sclerenchyma are absent.

Clade Heuchera

The phloem is not well structured (Fig. 16). In contrast to the clade Saxifraga all species contain crystal druses (Fig. 17). The phellem is never extremely thick.

Clade Bergenia

In the radial oriented strands of parenchyma cells distinct groups of small sieve tubes occur (Fig. 18). Bergenia species contain crystal druses in the large rays.

phe phe

Fig. 16. Sightly differentiated phloem. Parenchyma cells are often slightly larger than sieve tubes. The large cortex cells contain crystal druses. Rhizome of a 15 cm-high plant, moist conifer forest, hill zone, Coeur d'Alene, Idaho, USA. Tiarella unifoliata, transverse section.

Fig. 17. Crystal druses in the cortex. Rhizome of a 15 cm-high plant, garden, hill zone, Botanical Garden Zürich, Switzerland. Tiarella cordifolia, transverse section.

Left Fig. 14. Phloem and cortex with a uniform anatomy. Parenchyma and sieve tubes cannot be distinguished. Most cells contain nuclei and are therefore living. A phellogen produces a thick phellem. Rhizome of a 5 cm-high herb, meadow, alpine zone, Alps, Switzerland. Saxifraga moschata, transverse section.

Right Fig. 15. Exposed stem with an extremely thick phellem. Rhizome of a 5 cm-high herb, meadow, subalpine zone, Alps, Switzerland. Saxifraga oppositifolia, transverse section.

cry cry

100 Mm

Fig. 18. The living phlosem consists on gruops of small sieve tubes and larger parenchyma cells. Sieve cells in the older phloem are collapsed. Rhizome of a 15 cm-high succulent plant, Botanical Garden Halle, Germany. Bergenia ciliata, transverse

100 Mm

Fig. 18. The living phlosem consists on gruops of small sieve tubes and larger parenchyma cells. Sieve cells in the older phloem are collapsed. Rhizome of a 15 cm-high succulent plant, Botanical Garden Halle, Germany. Bergenia ciliata, transverse

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