Irmgard von Teichman

A re-evaluation of the structure of the mango ovule in comparison with those of a few other Anacardiaceae species

The mango ovule has been described by some authors as unitegmic and by others as bitegmic, but in the latter case with integuments fusing quite early. The results of this investigation suggest that it is a pachychalazal ovule in that the greater part of the ovular envelope consists of chalazal tissue and that only the micropyle is formed by one massive integument. The pachychalazal ovule could possibly be a characteristic of the tribe Anacardieae. Bitegmic ovules in which the outer integument is continuous with two labellate outgrowths of the massive funicle (‘raphe-chalazal ovules’) are apparently characteristic of the tribes Spondieae and Rhoideae. All previously investigated species as well as Sclerocarya birrea (A. Rich.) Hochst. subsp. caffra (Sond.) Kokwaro and Lannea discolor (Sond.) Engl. were found to be chalazogamous.

Reinterpretation of the pericarp of Rhus lancea (Anacardiaceae)

The limits of the exo- and endocarp s.str. and s.l. are defined. In Rhus lancea L.f. (tribe Rhoideae) the sclerenchymatous endocarp s.l. includes not only the inner stratified, but also the outer ridged part. The exo-, meso- and endocarp of R. lancea are briefly compared with homologous parts of the pericarp in five species of the tribe Spondieae. In the Anacardiaceae pericarp structure is of considerable taxonomic significance, particularly at the generic level. There is a need for more ontogenetic studies in this family to enable the comparison of homologous structures in the various taxa.

Pericarp and seed coat structure in Tapirira guianensis (Spondiadeae: Anacardiaceae)

Tapirira guianensis Aubl., a member of the Anacardiaceae from tropical South America, is characterized by a fleshy drupe with a relatively large, partially pachychalazal, exalbuminous seed. A distinctive feature of the exocarp sensu lato is the hypodermis with thickened secondary cell walls, whereas the mesocarp is a typical sarcocarp. The relatively weakly developed endocarp sensu lato , which does not differentiate any opercula, differs significantly from the massive, operculate endocarp reported for other members of the Spondiadeae. Structurally the seed coat of T. guianensis resembles that of related genera. The seed coat is of dual origin as it develops from the integument and the chalaza. It is undifferentiated in the sense that it lacks a definite mechanical layer. Species-specific differences in the Spondiadeae include the cell wall components of the hypostase, namely specific polysaccharides, phenolic compounds and callose. These unique features of the exocarp and seed coat of T. guianensis may possibly constitute an alternative evolutionary strategy within the Spondiadeae towards the protection of the embryo.

A preliminary study on the germination of Sclerocarya birrea subsp. caffra

Seeds of Sclerocarya birrea (A. Rich.) Hochst. subsp. caffra (Sond.) Kokwaro, commonly known as marula, occur in locules within a hard lignified endocarp. The endocarp appears to restrict germination mainly by offering mechanical resistance. It may also restrict the leaching of germination inhibitors and possibly serve as a barrier to oxygen diffusion. The endocarp does not restrict water uptake. High germination counts were only obtained by removing opercula. Leaching slightly improved germination of seeds in intact endocarps. The optimum germination temperature of opercula-removed seeds was between 27° and 37°C. Storage improved rate of germination.

Taxonomic position of Rhus problematodes (Anacardiaceae): Evidence from fruit and seed structure

This is the first report on the structure of the pericarp and seed coat of Rhus problematodes Merxm. & Roessl., a curious microphyllous shrublet of very limited distribution in the southern desert region of Namibia. Mainly on the basis of macromorphology, it was hitherto considered to stand somewhat apart from other African members of Rhus L. (sect. Gerontogeae Engl.). R. problematodes clearly agrees with other species of Rhus in its basic pericarp and seed-coat characteristics, including a single-seeded unilocular drupaceous fruit, parenchymatous mesocarp with secretory ducts, ridged outer endocarp, inner endocarp composed of three discrete layers, and an endotegmic, partially pachychalazal seed coat. The scarcity of stomata and heavy deposition of cutin in the exocarp possibly reflect adaptations to its arid habitat. Evidence from fruit and seed structure, combined with that from other sources, reconfirms the view that it is a highly specialized species of Rhus showing several xeromorphic, mainly macromorphological, reductions. The shared presence of glandular stellate hairs and reduced foliage leaves suggests that it might be closely allied to R. horrida Eckl. & Zeyh., a species from Namaqualand.

Fruit polymorphism in ephemeral species of Namaqualand. I. Anatomical differences between polymorphic diaspores of two Dimorphotheca species

Differences in germination behaviour between different diaspore types of Dimorphotheca sinuata DC. and Dimorphotheca polyptera DC. induced the morphological study of the above-mentioned species. The study reveals that the difference between the diaspore types lies in the structure of the pericarp. Pericarp characteristics such as presence of mucilage, tanniniferous substances and cuticles as well as extensive sclerenchymatous zones, are associated with those diaspore types with the poorest germination. Fruit polymorphism represents a survival strategy in these species from the arid Namaqualand.

The structure of the seed of Mangifera indica L. and notes on seed characters of the tribe Mangifereae (Anacardiaceae)

The anatropous, unitegmic and pachychalazal mango ovule develops into the campylotropous, pachychalazal seed. The undifferentiated seed coat is of dual origin, developing from the integument as well as from the pachychalaza. The term ‘peritesta’ is suggested for the peripheral, band-like integumentary part of the seed coat. The major saddle-shaped chalazal part is associated with a tanniniferous hypostase. The discussion includes the anatomy and histochemistry of the seed. The pachychalazal seed with undifferentiated seed coat probably characterizes the tribe Mangifereae. After consideration inter alia of seed characters, it is concluded that, according to generally accepted criteria, the Anacardiaceae is phylogenetically one of the more advanced forest families.

Fruit polymorphism in ephemeral species of Namaqualand. II. Anatomical differences between polymorphic diaspores of Arctotis fastuosa and Ursinia cakilefolia

The different colour diaspore types of Arctotis fastuosa Jacq. and Ursinia cakilefolia DC. were examined. Pericarp and seed coat anatomy revealed only minor differences between fruit morphs. Diaspores of A . fastuosa are characterized, amongst others, by a lens-shaped pericarp operculum and bubble-shaped, air-filled cells in the outer epidermis of the seed coat. The latter may represent a mechanism to protect the embryo against excessive heat.

Contributions to the floral morphology and embryology of Pavetta gardeniifolia A. Rich. Part 2. The ovule and megasporogenesis

In Pavetta gardeniifolia the ovule is hemitropous, unitegmic with a rudimentary nucellus and a monosporic, Polygonum -type embryo sac. The base of the ovule is encircled by an aril-like tissue with papillate cells secreting a mucilage in which the seed-borne leaf-nodulating bacteria are harboured. The ultrastructure of these cells as well as their relation to a true aril is discussed. Fertilization is porogamous. Endosperm development is nuclear and in the mature seed it is proteinaceous.

Contributions to the floral morphology and embryology of Pavetta gardeniifolia A. Rich. Part 1. The inflorescence and flower

The inflorescence of Pavetta gardeniifolia is a thyrse. The entire inflorescence as well as each unit develops in stipular cavities lined by dendroid colleters associated with leaf nodulating bacteria. Excepting the bicarpellate ovary, the epigynous flowers are tetramerous, gamopetalous with epipetalous stamens. The vascularization of the flower is discussed in detail.