The intergeneric hybrid genus Hippeastralia was formed when someone first crossed a Hippeastrum in the striatum group with Sprekelia formosissima (Pradhan, 1970). Both are in the Amaryllis Family (Amaryllidaceae) and in the New World tribe, HIPPEASTREAE.

I was very surprised to learn that the hybrid plants are very fertile, setting seed with pollen from a variety of related genera and species. They apparently set seeds with pollen from Hippeastrum, Sprekelia, Habranthus, and Zephyranthes.

Other Sources of Information

"An Apparent Sprekelia-Amaryllis Cross" by Udai Chandra Pradhan, in PLANT LIFE (HERBERTIA), vol. 26, p. 117 (1970).
Bulbous Plants of Southern Africa, by Neil du Plessis and Graham Duncan, Tafelberg Pub. Ltd., Cape Town (1989).
Bulbs for Warm Climates, by Thad M. Howard, University of Texas Press, Austin (2001).
Bulbs, Revised Edition, by John E. Bryan, Timber Press, Portland (2002).
Cape Bulbs, by Richard L. Doutt, Timber Press (1994).
RHS Manual of Bulbs, John Bryan and Mark Griffiths, Eds., Timber Press (1995).
Garden Bulbs for the South, Scott Ogden, Taylor Publishing Co., Dallas, TX (1994).
Bulbs of North America, Jane McGary, editor, Timber Press and North American Rock Garden Society (2001).
Bulbs for Summer Bloom, John Philip Baumgardt, Hawthorn Books Inc., New York (1970).