Portal de Periódicos da CAPES

Leaf surface and anatomy in Boraginaceae tribe Boragineae with respect to ecology and taxonomy

2001; Elsevier BV; Volume: 196; Issue: 4 Linguagem: Inglês

10.1016/s0367-2530(17)30056-7

1618-0585

Federico Selvi, Massimo Bigazzi,

Botany, Ecology, and Taxonomy Studies

The main anatomical and surface characters of the leaves of 54 specific and subspecific taxa belonging to 14 Boraginaceae genera of tribe Boragineae were analysed and compared by means of light and scanning electron microscopy. Characters concerning the vascular system appeared essentially uniform, while stomata size and density, structure of individual trichomes, type of indumentum, leaf and epidermis thickness and palisade arrangement were variable in the examined taxa. This variation was discussed in relation to the morphological and ecological diversification exhibited by the members of the tribe. Most species had typical dorsiventral leaves, but some showed an incipient isobilateral symmetry with a layer of abaxial palisade tissue. Thickness of the lamina and of the outer wall of the adaxial epidermal cells were higher in the xerophytic taxa, especially in the psammophytic species of Anchusa. The mesophytic genera Brunnera, Pentaglottis, Trachystemon and, partly, Symphytum had typical hypostomatous leaves, while the xerophytic and psammophytic species were characterized by increased stomatal density on the adaxial surface. This was higher in the taxa with thicker leaves. Abaxial stomatal density and size were inversely correlated. Mesophytic species had more densely spaced and smaller stomata than the xerophytic species. Finally, size of the abaxial stomata was higher in the taxa showing a thicker outer wall of the adaxial epidermal cells. Seven types of trichomes were recognized, five of which were eglandular and two glandular. Some of these types were systematically useful (exclusive to one or two genera) e.g., the hooked hairs of Symphytum and the lithocysts of Trachystemon and Brunnera. Energy dispersive X-ray microanalysis (EDX) showed that silica and calcium are the most abundant elements in the mineral deposits of the trichome cells. No strict correlation occurred between surface elements, trichome structure, edaphic requirements and systematic position of the 14 examined taxa, although the presence of small amounts of sulphur and phosphorus in Nonea and a remarkable abundance of Potassium in Nonea pulla and Pulmonaria picta could have systematic relevance.