Flower:

A single flower 1 to 2 inches across on a stout stalk floating on or rising above the water. Flowers are globular with 5 or 6 round bright yellow sepals that may be green on the outer surface near the base and may be dark red on the inside near the base. In the center are numerous yellow petals with dozens of similarly shaped stamens spirally arranged around a yellow central column. At the tip of the column is a red disk that typically has 8 to 15 rays, the edges of the disk straight to shallowly indented between the rays.

Leaves and stems:

Leaves are oval-oblong, 4 to 10 inches long, about 1½ times as long as wide, with a rounded tip and deep cleft at the base, the lobes at the base rounded and about half as long as blade's midrib. The basal lobes may be slightly separated, the gap between them (sinus) forming a narrow “V”, or the lobes may overlap.

Leaf stalks are flat and ribbon-like. Leaves are flat and float on the surface, occasionally submersed. The lower surface is often purplish on new leaves, the upper surface green to purplish.

Fruit:

Fruit, when formed, is a round to oval capsule ½ to 1 inch long, strongly ribbed and usually purplish brown, the red disk persisting at the tip and the capsule constricted just below it, the constriction up to 3/8 inch (10mm) in diameter.

Notes:

Intermediate or Red-disk Pond-lily is a natural hybrid between Yellow Pond-lily (Nuphar variegata) and Small Pond-lily (Nuphar microphylla), long suspected but recent DNA testing supports the lineage. It may be fertile or sterile and has characteristics intermediate between the parents:

• Flower 1 inch or more diameter, where N. variegata is up to 2½ inches and N. microphylla is ¾ inch or less.
• Leaf size 4 to 10 inches, the narrow sinus half as long as the midrib, similar to N. variegata where N. microphylla leaves are 4 inches or less with a wider sinus 2/3 as long as the midrib.
• Leaf stalk flat and ribbon-like, similar to N. varietata where N. microphylla stalks are flat to round in cross-section.
• Red disk at the tip of the flower's central column usually with 8 to 15 rays, similar to N. microphylla except 6 to 11 rays and more deeply scalloped edges, where N. variegata has a yellow to greenish disk with up to 28 rays.

The red disk is the more obvious difference between N. ×rubrodisca and N. variegata. The differences with N. microphylla flowers are more subtle but the leaf and flower sizes should be the more obvious distinctions.