1. Nuphar advena (Aiton) W.T. Aiton

N. lutea (L.) Sm. ssp. advena (Aiton) Kartesz & Gandhi

Pl. 460 b, c; Map 2089

Plants mostly emergent aquatics (sometimes floating-leaved or submerged), sometimes stranded on mud. Rhizomes relatively stout, sometimes somewhat flattened, light yellow, not producing tubers. Leaves submerged or more commonly floating or emergent; the submerged (overwintering and juvenile) leaves membranous (the margins appearing moderately to strongly undulate or crisped), short-petiolate; the floating and emergent leaves leathery and mostly long-petiolate (shorter in plants stranded on mud). Leaf blades 6–40 cm long and wide, nearly circular to ovate or broadly elliptic-ovate, rounded at the tip, attached in the sinus of a V-shaped, deeply cordate base, the lobes rounded at the tip, mostly bright green (often olive green to yellowish green in submerged leaves), the upper surface (except in submerged leaves) usually shiny, the undersurface glabrous or occasionally sparsely short-hairy, the venation mostly pinnate. Flowers emergent or appearing floating, 1.8–4.5 cm in diameter when open, hypogynous, the stalk relatively stout, not coiling as the fruits mature, glabrous or occasionally sparsely hairy. Sepals 6(–9), 1.0–2.3 cm long, elliptic to oblong-elliptic, broadly ovate or nearly circular, rounded to truncate or very shallowly notched at the tip, strongly concave, ascending to somewhat spreading and remaining cupped around the pistil at flowering, the outer 3 or 4 sepals smaller, green or reddish-tinged on one or both surfaces, the inner 3–5 sepals larger, green (occasionally reddish-tinged) toward the base and on the outer surface, yellow or sometimes reddish-tinged above the often green basal portion on the inner surface, more or less persistent at fruiting. Petals numerous, inconspicuous, reduced to relatively thick, oblong, scalelike organs positioned below and similar in size and shape to the stamens, shorter than the sepals. Stamens 3–9 mm long, mostly truncate at the tip. Ovary superior, the perianth and stamens attached at its base. Stigmatic disc 6–28 mm in diameter, circular, unlobed, with 8–24, raised, linear to narrowly oblong or narrowly lanceolate, stigmatic regions. Fruits capsular, 1.5–5.5 cm long, globose to ovoid, somewhat ribbed longitudinally, green or reddish-tinged, irregularly dehiscent around the basal portion with age. Seeds obovoid, 3–6 mm long, the surface smooth, green to brown, lacking an aril. 2n=34. May–October.

Scattered in the Ozark, Ozark Border, and Unglaciated Plains Divisions, north locally to Lincoln County and southeast locally to Dunklin County (eastern U.S. west to Wisconsin and Texas; Mexico, Caribbean Islands). Ponds, lakes, slow-moving to stagnant portions of streams, rivers, and spring branches, sloughs, and fens.

C. R. Robertson (1889a) observed Illinois plants of N. advena and suggested that pollination was mainly by bees and flies, with beetles consuming floral tissues but not effective pollinators. In contrast, Schneider and Moore (1977) studied Texas plants and concluded that beetles were the dominant pollinator, with flies and bees also contributing to pollination. Lippok et al. (2000) studied pollination and insect visitation in N. advena, including a population of ssp. ozarkana in Butler County. They documented visitation by a number of bees, flies, and beetles, all of which served as pollinators. These authors concluded that the relative abundance of local pollinators was a more important factor than the types of insect in determining which insects accounted for the most pollination. Flowers of Nuphar open only slightly to uncover the stigma during their first day and are then functionally pistillate. They close in the evening, often trapping beetles in the flower overnight. The second day, the flowers open more fully and are functionally staminate. Flowers continue to open for one to three subsequent days and presumably continue to shed pollen until the point when the ovary begins to swell and the perianth begins to decompose (Schneider and Moore, 1977).

Until recently, species limits in the N. lutea complex were controversial, with some authors preferring to consider the North American and Eurasian populations part of the same species under the name N. lutea (L.) Sm. (Beal, 1956). Padgett et al. (1999) and Padgett (2007) provided convincing evidence from morphological and molecular analyses that the New World plants are not as closely related to those in the Old World as previously thought and that they should be treated as two separate species. A number of infraspecific taxa also have been accepted over time; for example, Beal (1956) recognized seven subspecies as occurring in North America, some of which subsequently have been considered full species. Most recently, Padgett (2007) restricted N. advena to only four subspecies, the widespread ssp. advena and three regional endemics, one of which occurs in Missouri. The other two subspecies, ssp. orbiculata and ssp. ulvacea, are endemic to northern Florida and adjacent portions of Alabama and Georgia. The former has nearly circular, deeply notched leaf blades that are densely hairy beneath and relatively large flowers; the latter has more or less lanceolate, shallowly notched leaf blades that are glabrous beneath and relatively small flowers.