Domatia in seedlings

In recent years considerable interest has been taken in the characteristics of seeds and seedlings, especially those of rainforest species. The rapid destruction of the world’s rainforests is the cause of great concern to many. Efforts at rehabilitation and reafforestation can be assisted considerably if seedlings can be readily recognised and their ecological requirements ascertained. Many botanists such as Duke (1965, 1969) and Burger (1972) are endeavouring to add information on this aspect of rainforest ecology. Systematic botanists also find characters of seedling morphology and anatomy useful as evidence of relationships at various levels of taxonomy, and also in some cases, Bailey (1956), as evidence in phylogenetic studies. One character which occurs in many rainforest species is the presence of domatia — small structures occurring on the lower surface of the leaf blade in or very close to the vein axils. They may be in the form of a pit in the leaf tissue, a pocket formed by a connection of tissue across a vein axil, a tuft of hairs or a dome of tissue elevated above the leaf surface with an opening in or near the centre. These four — pit, pocket, hair-tuft and dome — are, following Jacobs (1966a), the basic elemental types. In some cases, a domatium may have a structure in which elements are combined. Domatia occur only in woody dicotyledons, trees, shrubs or vines, and in the majority of cases, those species are of humid forest origin. Often they are quite distinctive and their presence has been used as a supporting character in systematic studies of tropical and subtropical floras. To date they have not been recorded in seedlings.