Characteristics of the xylem

Annual rings occur in the present material in all Armeria species of the temperate zone (Figs. 1 and 2). Rings are often absent or indistinct in species growing in the Mediterranean and subtropical climate (Dyerophytum, Limonium and Plumbago; Fig. 3). Ring boundaries of the four Armeria species are defined by semi-ring porosity (Fig. 1). Diffuse porosity is characteristic for all other species (Fig. 3). Vessels of the genera Armeria, Limonium and Limoniastrum are predominantly solitary (Figs. 1 and 3). Radial multiples are characteritic of Dyerophytum in-dicum (Fig. 9) and Plumbago zeylanica (Fig. 14). Vessel diameter is <20 pm in all Armeria species (Fig. 1) and Limonium pectinatum. Vessel density varies mostly between 300-500/ mm2. Vessels of most species are thick-walled (Figs. 1 and 3), except in Dyerophytum indicum and Plumbago zeylanica. Vessels contain exclusively simple perforations. Inter-vessel pits are predominantly scalariform and pseudoscalariform in Armeria (Fig. 4), and small and round in all other species (Fig. 5). Spiral thickenings are absent from the present material. Dark-staining substances were observed in few cells of Limonium pectinatum.

The radial walls of fibers are perforated by very small (<2 pm) slit-like or round pits in all species. Septate fibers occur only in Dyerophytum indicum (Fig. 6). Fibers are either thin- or thin-to thick-walled in Armeria, Dyerophytum and Limoniastum monopetalum. They are thick-walled in Limoniastrum guyonia-num and both Limonium species (Fig. 7). Fibers are absent from Armeria alpina and A. arenaria (Fig. 1). Living, thick-walled fibers with nuclei are found in Limonium pectinatum (Fig. 8). Paratracheal parenchyma occurs in all species (Fig. 9) except Armeria, where parenchyma is pervasive (Figs. 1 and 2). Marginal parenchyma bands are distinct in Limonium pectinatum. Storied structures tend to be absent or indistinct. Rays are absent from pa pa pa pa

Left Fig. 1. Semi-ring-porous xylem with a distinct annual ring boundary. The thick-walled solitary vessels are surrounded by a pervasive parenchyma. Fibers are absent. Root collar of a 15 cm-high chamaephyte, meadow, subalpine zone, Pyrenees, Spain. Armeria alpina, transverse section.

Right Fig. 2. Slightly semi-ring-porous xylem. The thick-walled fiber groups (red) are surrounded by a pervasive parenchyma. Root collar of a 15 cm-high chamaephyte, meadow, coastal zone, Devon, Great Britain. Armeria maritima, transverse section.

Left Fig. 3. Diffuse-porous xylem with an indistinct ring boundary. Thick-walled vessels are solitary or in small groups and are surrounded by vasicentric, paratracheal parenchyma. Stem of a 50 cm-high dwarf shrub, sand dune, Mediterranean, coastal zone, Cadiz, Spain. Limoniastrum mono-petalum, transverse section.

Right Fig. 4. Imperforate and scalariform vessel pitting. Root collar of a 15 cm-high chamaephyte, dry meadow, mountain zone, France. Armeria arenaria, radial section.

Armeria maritima (Fig. 2). A few large rays divide rayless parts in the other Armeria species (Fig. 12). All other species have 3-6-seriate rays (Fig. 11). Ray cells are thin-walled and unligni-fied in Limonium pectinatum and primarely square or upright. Successive cambia occur in Dyerophytum indicum (Fig. 13) and in Plumbago zeylanica (Fig. 14), but are absent from all other species analyzed. Crystals are very rare. Prismatic crystals occur only in Limoniastrum guyonianum.

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