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

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

CABOMBACEAE. The adventitious roots of Brasenia schreberi and Cabomba caroliniana are small with very small steles and little lignified, mature primary xylem (Fig. 15); often in C. caroliniana roots there is no mature xylem (Fig. 16). The endodermis in each species has Casparian bands (Fig. 17, 18) and suberin lamellae (Fig. 16, 19), but in both Brasenia and Cabomba the suberin lamellae are more prominent on the outer tangential walls than elsewhere in the cells (e.g., Fig. 16). The aerenchyma lacunae are hexagonal in Brasenia (Fig. 17) and mostly radial in Cabomba (Fig. 18), and there are no sclereids. The hypodermis is composed of a uniseriate exodermis which has Casparian bands (Fig. 15, 18) and suberin lamellae (Fig. 16, 19). Usually, in Brasenia and Cabomba there is only one Casparian band per exodermis cell, but two may be present (Fig. 18). The suberin lamellae may be more prominent on the inner walls of the exodermis (Fig. 16). Acid digestion reveals the wavy Casparian bands of the small endodermis cells and larger exodermis cells (Fig. 20). These roots are usually enclosed by an epidermis.

NELUMBONACEAE. Nelumbo lutea and N. nucifera roots have a stele usually with a distinctive pith of sclerenchyma cells within 7-9 primary xylem strands (Fig. 21); some roots have metaxylem embedded near the center of the sclerenchyma (Fig. 22). In the mature root, the Casparian bands (Fig. 21) of the endodermis are always overlain by suberin lamellae (Fig. 23) and secondarily lignified cell walls (Fig. 22, 24). The hypodermis is multilayered, and its outermost layer of cells is a uniseriate exodermis with Casparian bands (Fig. 21) and suberin lamellae (Fig. 23). The adjacent layers of hypodermis are not exodermal, although they have distinctive patterns of lignified cell walls in somewhat regularly spaced lignified cells in N. nucifera (Fig. 21) and in one-two layers of lignified cells in N. lutea (Fig. 22). Acid digestion reveals that endodermal and exodermal Casparian bands are similar in size and waviness, although the cells with lignified walls make the hypodermis thicker (Fig. 25). There are no cortical sclereids (e.g., Fig. 21), and the aerenchyma has hexagonalshaped lacunae (Fig. 21). An epidermis is usually present.

Discussion. While little is known about the characteristics of the roots of the Nymphaeaceae, Cabombaceae, and Nelumbonaceae (see Schneider and Williamson, 1993; Williamson and Schneider 1993a, 1993b; Metcalfe and Chalk 1950), except for certain xylem characteristics (see Schneider and Carlquist 1995a, 1995b1, 1996a, 1996b; Schneider et al., 1995), my study shows that there are distinguishable differences among their root cortices.

In mature roots, the endodermis cell wall of the Nymphaeaceae, with two minor exceptions where there are faint suberin lamellae in old roots, is made only of Casparian bands, whereas in the Cabombaceae, even with smaller roots, the endodermis has Casparian bands and suberin lamellae. In the Nelumbonaceae, there are secondarily lignified walls overlying the suberin lamellae and Casparian bands.