root cortex of the nymphaeaceae, cabombaceae, and nelumbonaceae1, The

Journal of the Torrey Botanical Society, Jan-Mar 2002 by Seago, James L Jr

All water lilies and lotuses studied have aerenchyma. The Nymphaeaceae are characterized by having many SRH cells of the hexagonal aerenchyma modified into astrosclereids (termed idioblasts by Conard, 1905; see Seago et al., 2000b) and by transverse diaphragms (Conard, 1905; Seago et al., 2000b). No sclereids or transverse diaphragms occur in the Cabombaceae or Nelumbonaceae. Like their leaves (Rao and Bannerjee, 1979), the roots of the Nymphaeaceae are characterized by abundant astrosclereids at maturity (see also Conard, 1905; Schneider and Carlquist, 1995a, 1995b, for Euryale, Victoria and Barclaya; Seago et al., 2000b, for Nymphaea odorata), thus differing distinctly from the Cabombaceae and Nelumbonaceae. The lack of sclereids in mature roots parallels the situation described by Rao and Banerjee (1979) in the leaves of Cahomba and Brasenia (see also Williamson and Schneider, 1993) and in Nelumbo (see also Goleniewska-Furmanowa, 1970) where there are no sclereids. However, it should not be surprising that I could not find sclereids in Victoria in the few young roots that I observed, because the young roots of the other genera and species of Nymphaeaceae also lacked sclereids. The possibility of contractile roots, as reported by Conard (1905), crystals, or other inclusions was not considered in this study.

The hexagonal pattern of lacunae in the aerenchyma, characteristic of all Nymphaeaeceae, Nelumbonaceae, and Brasenia but not Cabomba also reflects the pattern of apical meristem organization and the normal pattern of cell derivation in the ground meristem (see Clowes, 1994, 2000; Seago et al., 2000b); that is, most files of cells are present near the apex, even when closed meristems are present in Nelumbo and Brasenia. In open meristems like Nymphaea the cortical files arise as distinct files abutting the layer of initials (Clowes, 1994, 2000; Seago et al., 2000b). This pattern, whereby radial files of cells across the cortex with cubic packing are not produced, appears to be necessary to produce such hexagonal packing of aerenchyma (Seago et al., 2000b). The closed meristem of Cabomba as characterized by Clowes (1994, 2000), is condusive to regular, radial cell files in the ground meristem that would produce cubic packing and radial lacunae in the cortex (Seago and Marsh, 1989). The apparent presence of closed meristems and the addition of cell files in the middle ground meristems of Barclaya, Nuphar and Nelumbo (Clowes, 1994, 2000), however, illustrate the need for further study of cortical development in these genera.

The hypodermis of the Nymphaeaceae and the Cabombaceae has a uniseriate exodermis of Casparian bands and suberin lamellae; in the Nymphaeaceae, the exodermis in N. odorata may have secondary cellulose walls in mature roots (Seago et al., 2000b). The inner layers of non-exodermal hypodermis are usually not modified. The Nelumbonaceae has a complex hypodermis with a uniseriate exodermis with Casparian bands, suberin lamellae, and secondarily lignified walls, and there are either full or partial inner two layers of non-exodermal hypodermis that have lignified walls.