This is the fertile version of the much coveted ruffled sterile 'Crispum' forms of the Hart's-tongue fern. The best forms of 'Undulatum' pull the edges of the undulating blade into a spiral as if the fronds were whirligigs in motion creating a wonderful effect like a ruffled seaweed.  I have seen several rather poor forms being labeled as this which are merely typical of the normal range of variation within the species with slightly wavy edges that simply don't deliver the same impressive habit.

Frond Condition:  Evergreen
Mature Height:  6-12"
Origin: English cultivar
Cultural Requirements:  Partly Shaded, Full Shade, Evenly Moist, Slightly Moist, Calcium
USDA Zones:  6, 7, 8, 9