Epidermal and morphological studies in the Asteraceae.
Morphological and epidermal features of fifteen members representing five tribes of the family Asteraceae (Compositae) were studied. The leaves varied in size, colour, shape, margin and texture, with Emilia being the most divergent owing to its variable leaf shape, obtuse apex, winged base, yellowish green colouration and glabrous surface. The small florets organized into homogamous or heterogamous capitula, different size and shape classes of leaves, complex patterns of venation and annual or perennial herbaceous habit highlight the advanced condition of the family. The size of the stomatal complex, type of stomata and the number of subsidiary cells varied considerably. Irregular epidermal cells with undulating walls, abnormal stomata with single or degenerating guard cells and contiguous stomata were observed. Elephantopus possessed up to five different types of trichomes. The Hierarchical Cluster Analysis reveals that Helianthus is very distinct from all the other members, followed by Elephantopus and Emilia, which form separate groups. Hence it is suggested that Helianthus may be separated from the tribe Heliantheae and included under a new tribe recent observation of knotted 1-like genes in the active stage in the leaves, stems, and inflorescences of Helianthus by Tioni et al. (2003) based on Northern blot experiments. The placement of Emilia in a separate tribe Senecioneae is justified in the present analysis. Separation of the sub-tribe Elephantopus from Vernoniiae based on clustered heads and reduced or modified pappus (Robinson, 1999) gains support in this study.