E.L. Kotina

Bark anatomy of Adansonia digitata L. (Malvaceae)

ABSTRACT The bark structure of Adansonia digitata L. is described in detail. Characters of the bark that are shared with other Malvaceae include the presence of strongly dilating rays, mucilage cells and cavities, druses of calcium oxalate in the cells of cortical parenchyma and phloem rays, a storied arrangement of sieve tube members and axial parenchyma strands, the presence of secondary phloem fibers and their arrangement into tangential bands. The secondary phloem fibers are longer (2.8–8.6 mm) and more abundant than the libriform fibers (1.7–2.2 mm) in the wood of this species. The abundance of parenchyma in both axial and radial parts of the secondary phloem and in the pseudocortex is a noteworthy feature. Due to the complementarity of fibrous and parenchymatous tissues, the secondary phloem can provide substantial mechanical benefits and apparently play an important role in the biomechanical stability of the trunk. The meristematic capacity of dilated phloem rays and the pseudocortex allow for substantial bark dilatation with very limited abscission of the outer portions of the secondary phloem. Subsequent phellogen initiation in the outer part of the secondary phloem was not observed, not even in mature bark. Hence no rhytidome is present. The thin translucent phellem, formed by continuous phellogen arising in the subepidermal layer, allows for photosynthesis to potentially occur within the chloroplast-containing cells of phelloderm and pseudocortex, even when the plants are leafless, thus probably assisting them to survive harsh climatic conditions. The formation of sieve tube members by transverse anticlinal divisions from fusiform cambial initials in A. digitata is a first report for the Malvaceae sensu lato.

“Hairy” bark in Lannea schweinfurthii (Anacardiaceae): hyperhydric-like tissue formed under arid conditions

ABSTRACTA remarkable, almost fur-like “indumentum” of velvety “hairs” (sometimes referred to as “fungi”) occurs on the roots (and to a lesser extent also on the trunk) of Lannea schweinfurthii var. stuhlmannii and is known as vhulivhadza in the Venda language (Tshivenḓa). The hairs are traditionally used by the Venda people (Vhavenḓa) of the Limpopo Province of South Africa, for various biocultural purposes. A detailed anatomical study of the origin, structure and development of these unusual “hairs” showed that they are of peridermal origin and develop from dense clusters of phelloid cells which are scattered within the stratified phellem. These cells are capable of considerable radial elongation thus forming hair-like radial files of elongated phelloid cells. The “hairy” patches on the bark may also develop from lenticels which become hypertrophied. These clusters of phelloid cells resemble the hyperhydric tissue which is reportedly formed in periderm of stems exposed to a water-saturated environment in some plant species. The formation of hyperhydric-like tissue in roots and stems of L. schweinfurthii var. stuhlmannii occurs, however, under relatively arid conditions. Since this tissue contains large intercellular spaces, it may also be regarded as a specialized type of aerenchymatous phellem. The adaptive significance, if any, of the phelloid “hairs” remains unknown.

Bark and wood anatomy of Leucosidea and Cliffortia (Sanguisorbeae, Rosaceae)

The wood and bark structure of Leucosidea sericea and two species of Cliffortia, the South African members of the tribe Sanguisorbeae (Rosaceae) are described. These two genera share few anatomical traits (the presence of schizo-rhexigenous intercellular spaces in the cortex, almost exclusively simple perforation plates, small alternate intervessel pits, etc.) with other Rosaceae. However, Leucosidea shows a distinct storied structure of the secondary phloem and wood as well as stratification of the secondary phloem, with conductive elements and nonsclerified crystalliferous axial parenchyma arranged into alternating bands. These conditions are recorded for the first time for the family Rosaceae. In contrast to Leucosidea, two species of Cliffortia show neither storied structure of secondary phloem and xylem, nor stratification of secondary phloem.