Epidermal patterning in seedling roots of eudicotyledons

Three types of epidermal patterning occur in roots of angiosperms: in Type 1, all the epidermal cells can potentially produce root hairs (hair cells); in Type 2. asymmetric cell divisions produce short cells that develop into hair cells and larger cells that do not (non-hair cells); and in Type 3. hair cells occur in files separated by one to three files of non-hair cells. In the present study we examined the epidermal patternings of seedling roots of 77 eudicotyledonous species from 43 families. We found that Type I patterning was the most common and no species had Type 2 patterning. Previously, Type 3 epidermal patterning had been described only in the family Brassicaceae. In addition to the Brassicaceae (including the Capparaceae), we found Type 3 patterning in the Brassicales families Limnanthaceae and Resedaceae, whereas the other Brassicales families we examined, Caricaceae and Tropaeolaceae: had Type 1 patterning. We also found Type 3 patterning in six families of the Caryophyllales sensu late: Amaranthaceae, Basellaceae, Caryophyllaceae, Plumbaginaceae, Polygonaceae and Portulacaceae. However, the family Cactaceae, which is also in this order, had Type 1 patterning. Only one other species, Nemophila maculata (Boraginaceae), had Type 3 patterning; the other two species that we examined in this family had Type I patterning. Type 3 patterning thus occurs more widely in the eudicotyledons than was previously thought. (C) 2001 Annals of Botany Company.