Pygmy water-lily, small white water-lily

Castalia leibergii Morong; Nymphaea tetragona Georgi subsp. leibergii (Morong) A. E. Porsild

Rhizomes unbranched, erect, cylindric; stolons absent. Leaves: petiole glabrous. Leaf blade abaxially green to deep purple, adaxially green, ovate to elliptic, 3-19 × 2-15 cm, margins entire; venation radiate centrally, without weblike pattern, principal veins 7-13; surfaces glabrous. Flowers floating, 3-7.5 cm diam., opening and closing diurnally, only sepals and outermost (occasionally innermost) petals in distinct whorls of 4; sepals uniformly green, obscurely veined, lines of insertion on receptacle not prominent; petals 8-15, white; stamens 20-40, yellow, connective appendage projecting less than 0.2 mm beyond anther; filaments widest above middle, much longer than anthers; pistil 5-12-locular, appendages at margin of stigmatic disk tapered or slightly boat-shaped, 0.6-1.5 × 0.8-1.4 mm. Seeds ovoid, ca. 2-3 × 1.5-2 mm, ca. 1.3-1.5 times as long as broad, lacking papillae on surface.

Flowering summer. Ponds, lakes, and quiet streams; 0-1000 m; Alta., B.C., Man., Ont., Que., Sask.; Idaho, Maine, Mich., Minn., Mont.

Although widely distributed in northern North America, Nymphaea leibergii is apparently not common in much of its range. It is closely related to N . tetragona (see also), with which it has been confused; it differs in a number of floral and foliar characteristics. Although the two species are sympatric over central and western Canada, the distinctions are maintained. Coexistent populations are unknown at this time; such populations would provide useful study opportunities and should be sought in the area of overlap, especially in southeastern and central Manitoba and east-central British Columbia where nearby populations exist.

A presumed natural hybrid between Nymphaea leibergii and N . odorata subsp. odorata has recently been found by Hellquist in northern Maine. It is intermediate in morphology between the two parental species and appears to be sterile.