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

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

SEAGO, JR., J. L. (Department of Biology, State University of New York, College at Oswego, New York 13126) The Root Cortex of the Nymphaeaceae, Cabombaceae, and Nelumbonaceae. J. Torrey Bot. Soc. 129: 1-9. 2002.-The roots of selected water lilies, Nymphaeaceae and Cabombaceae, and water lotuses, Nelumbonaceae, were examined using epifluorescence, brightfield, and modified darkfield microscopy to determine the characteristics of root cortical structure. The members of the Nymphaeaceae have an endodermis usually with Casparian bands only, many astrosclereids and some transverse diaphragms scattered throughout the aerenchyma, and a hypodermis with a uniseriate exodermis with Casparian bands and suberin lamellae, although there may be some secondary, cellulosic thickening. The Cabombaceae are characterized by small roots with an endodermis with Casparian bands and uneven suberin lamellae, aerenchyma without sclereids or diaphragms, and an exodermis with Casparian bands and distinctive suberin lamellae. The Nelumbonaceae are distinctly different: Nelumbo has an endodermis of Casparian bands, suberin lamellae, and secondarily lignified walls, an aerenchyma without sclereids or diaphragms, and a multiseriate hypodermis with a uniseriate exodermis of Casparian bands and suberin lamellae, and an inner hypodermis with distinctly lignified walls.

Key words: aerenchyma, Cabombaceae, endodermis, exodermis, hypodermis, Nelumbonaceae, Nymphaeaceae, root cortex, sclereids, water lilies, water lotuses.

The water lilies, Nymphaeaceae and their Cabombaceae relatives, and the water lotuses, Nelumbonaceae, are spectacular, horticulturally valuable plants whose flowers and leaves have been studied much over the decades (Schneider and Williamson, 1993; Williamson and Schneider 1993a, 1993b), but whose roots have been sparingly studied, probably because they are unseen. The monograph of Conard (1905) is the seminal work on the structure and development of water lily plants in the genus Nymphaea including the roots, and the Schneider and Carlquist studies (Schneider and Carlquist 1995a, 1995b, 1996a, 1996b; Schneider et al., 1996) have provided information about the nature of the xylem in the roots of these groups. Some information on the root apical meristems has also been provided by the studies of Voronkina (1974) and Clowes (1994, 2000), and Seago et al. (2000b) have recently provided analyses of Nymphaea odorata root cortical development and structure. The relative status of our knowledge about the roots of the various water lilies and lotuses is summarized best by Schneider and Carlquist (see above), Schneider and Williamson (1993), and Williamson and Schneider (1993a, 1993b). More recent information on the phylogeny of these families, i.e., removing the Nelumbonaceae from the Nymphaeaceae (Les et al., 1997; Soltis et al., 1999; Qiu et al., 1999), has made the present study timely.

I have been pursuing a long-term study of the root cortex of flowering plants to characterize the various patterns of aerenchyma, endodermis, and hypodermis development and structure found in the roots of wetland plants (Seago and Marsh, 1989; Seago et al., 1999a, 1999b; Seago, et al., 2000a). The water lily root cortex, even with seemingly very distinctive structural features, has been studied very little since Conard (1905), except for the Seago et al. (2000b) study which included Nymphaea odorata.

My objectives in this paper are to illustrate the variations in root cortex structure for representative genera and species of the Nymphaeaceae, Cabombaceae, and Nelumbonaceae and to determine if root traits reflect the recent phylogenetic analyses.

Materials and Methods. Root specimens from the bases of adventitious roots of several genera and species were obtained from plants growing either in wetlands (Black Creek Marsh, Cayuga County, NY; Silver Lake, LaPorte County, IN) or from cultivated pools at botanical gardens (Longwood Gardens, Kennett Square, PA) or at commercial growers (Lilypons Water Gardens, Buckeystown, MD; Country Herbs and Flowers, Fulton, NY: Landmasters Group, North Syracuse, NY; Crystal Palace Perennials, St. John, IN); for some species only a few young roots were obtained from plants in botanical gardens, usually in late summer. Specimens from Longwood Gardens and Lilypons Water Gardens were collected by their professional staff in my presence, and photographs had to be used as vouchers. The plants examined were members of the Nymphaeaceae (Euryale ferox Salisb., Nuphar luteum (L.) Sm., Nymphaea x ampla (Salisbury) de Candolle 'Wood's Blue Goddess' John Wood [hereafter, Nymphaea 'Wood's Blue Goddess'], Nymphaea mexicana Zuccarini, Nymphaea odorata Ait., Nymphaea x odorata Alton 'Caroliniana Nivea' J.B.L. Marliac [hereafter, Nymphaea 'Caroliniana Nivea'], Nymphaea tetragona Georgi, Nymphaea tuberosa Paine, Victoria cruziana d'Orbigny x V. amazonica (Poeppig) Sowerby 'Longwood Hybrid' Patrick Nutt [hereafter, Victoria]), Cabombaceae (Brasenia schreberi Gmel., Cabomba caroliniana Gray), and Nelumbonaceae (Nelumbo lutea (Willd.) Pers., N. nucifera Gaertn.). As soon as the roots were obtained, they were sectioned with a razor blade and placed on labeled microscope slides in 80% glycerine. The sections were examined either without staining under brightfield or under epifluorescence in UV light (Seago et al., 1999b), or they were rinsed in dH2O, followed by various kinds of staining or treatments (berberine hemisulfate counter-stained in aniline blue or toluidine blue O, Fluorol yellow, Sudan red 7B, phloroglucinol-HCl, toluidine blue O, or sulfuric acid) to reveal different cell wall structures (Casparian bands, suberin lamellae, secondary cell walls) and wall chemicals (cellulose, lignin, and suberin); the staining procedures of Seago et al. (1999b, 2000b) were followed. Specimens were observed and photographed with a Zeiss Axiophot epifluorescence microscope under UV light (excitation filter UV-G, chromatic beam splitter FT 395 nm, barrier filter LP 420 nm), a Nikon Labophot brightneld microscope, or a Swift phase contrast microscope modified for darkfield in order to observe specimens digested with sulfuric acid to reveal Casparian bands.