Parsimony analysis of matK sequence data for representatives of Myrtaceae s.1. provides evidence of its potential in phylogenetic inference in this family. Psiloxylon and Heteropyxis comprise a robust clade, basal to representatives of Myrtaceae s. str., and strongly clustered with it. In a limited sample of Myitaceae s. str., several strongly supported groups are identified: the myrtoid genera (excluding Syzygium), representatives of the Chamelaucium alliance, and the Chamelaucium plus Leptospennum alliances.
The pollen morphology of 28 species from the subtribe Metrosiderinae (s.Bentham) is described and compared in the light of several recent taxonomic revisions of this subtribe. All species have the same basic Myrtaceous pollen type, but there is intra and interspecific variability seen in a number of the pollen characters. Intraspecific variability is related either to changes in volume and size of the pollen grain or to the occurrence of polar islands. It is concluded that the character of syncolpy or parasyncolpy as relating to the presence or absence of polar islands may not be taxonomically reliable at the species level. Interspecific variation. and thus those characters most useful in assessing the taxonomy, relate to the structure of the angle of the amb, the exine structure and sculpture and the definition, form and type of colpi and apocolpia. One species shows a difference in polarity from the rest. Three basic exine sculpture types were defined, but it was necessary to examine them under the scanning electron microscope (SEM) because their patterns could not be resolved under the light microscope. Acetolysis enhanced the definition of the smaller basic sculptures under the SEM. Generally, the pollen morphology of these species was found to support the recent taxonomic revisions of this subtribe.
The morphology and development of the circular bordered pits on the transfusion tracheids in the leaves of Callitris muelleri are described from light microscopy of semithin sections and SEM studies of cut surfaces. Two parallel bars of thickening develop on the pit border either side of the aperture, and trabecula-like outgrowths develop into the cell lumen from the centre of each bar. These outgrowths are often contorted and may anastomose with the wall or each other. Development is arrested at the barred stage in occasional pits, and both 'barred' and 'trabeculate' pits may occur in the one cell. 'Trabeculate-pitting' occurs in all species of Callitris and Actinostrobus, and was also observed in species of Cupressus and Juniperus. Previous reports of outgrowths on pits in several species of the last two genera suggest that the trabeculate pit is characteristic of both. 'Barred pits' occur in Widdringtonia cupressoides and Catocedrus decurrens. Unadorned circular bordered pits are characteristic of Diselma archeri, and have previously been reported in a range of genera in the family. These three types of pit are considered to represent an evolutionary transformation series in which the last type is plesiomorphic. The occurrence of the apomorphic conditions in both northern and southern hemi- sphere genera does not fit well with the present taxonomy of the family. The probable adaptive significance of the trabeculate pit is discussed.
Exine ultrastructure has been determined by transmission electron microscopy analysis of the grains of a number of species of Myrtaceae, chosen to represent some of the diversity of sculpture and structure that can be observed using light microscopy and scanning electron microscopy. The species all show a typical angiosperm exine differentiation consisting of two chemically different layers, an electron-dense ektexine and a less dense endexine divided by a very thin electron-transparent lamella. They all differ, however, from the typical angiosperm architecture by the presence of a somewhat unstructured, granulate infratectal layer and a granular/alveolate endexinous layer around the pores. Species differences relate to the granulate coiumellate organization of the infractectal layer, the extent or density of tectal perforations and the presence and thickness of a foot layer around the grain.
Aluminium chloride-induced fluorescence was used to localize biflavonoids in fresh leaf sections of Agathis robusta. This method indicates that the biflavonoids are confined to the outer periclinal wall and anticlinal walls of the epidermal cells. This was confirmed by extraction and chromatographic analysis of epidermal peels, cuticular scrapings and middle leaf tissue fractions.A survey of representatives of the Psilotales, and of all orders of the gymnosperms using aluminium chloride-induced fluorescence, indicates that localization of biflavones in the cuticle is a general feature of biflavonoid-containing plants. Members of the Pinaceae and Gnetales, in which biflavonoids have not been found, show no such fluorescence in the cuticle. The possible functional roles of biflavonoid accumulation are discussed. It is postulated that biflavones serve a protective role against invasion of the leaf by microorganisms and/or attack by leaf-eating insects.Leaves of Agathis robusta were particularly suitable material in which to localize the biflavonoid fraction. Previous studies o n the leaves of this and several other species of the genus Agathis (Khan et al. 1972;Varshney et al. 1973) indicated that biflavonoids constitute by far the major proportion of the flavonoid fraction. Furthermore, unlike the scale-leaves of many conifers, the broad dorsiventral leaves of Agathis species are relatively easily separable into epidermal and mesophyll fractions, allowing confirmation of observations by t.1.c. analysis of extracts from these fractions. For these reasons the study concentrates o n Agathis robusta. However, a brief survey of the aluminium chlorideinduced fluorescence i n representatives of all orders of gymnosperms, as well as the Psilotales, is also included. Materials and MethodsUnless otherwise stated, all studies were carried out on mature leaves of specimens cultivated in the grounds of the University of New South Wales: voucher specimens have been lodged with UNSW.
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