Summer–long golden panicles of flowers spring forth from thyrallis, the new Texas Superstar®. Thryallis, Galphimia glauca, grows to be a handsome 4' to 6', rarely 9', tall evergreen shrub in USDA zones 9 to 11. It can function as a dieback shrub or herbaceous perennial in warmer parts of zone 8b. The foliage either remains evergreen, or on the margins of its cold tolerance limits may turn a rich red–bronze color during winter. Further north the stems and foliage may be killed. Thyrallis will serve in a wide range of functions appropriate for evergreen shrubs in the southern half of the state. In colder portions of Texas, thryallis serves as a good patio container plant or seasonal summer in–ground accent.
Thyrallis produces a dense attractive rounded canopy of bluish green foliage topped by showy spire–like inflorescences. The foliage is a great foil for the 2" to 4" long terminal panicles of ½" to ¾" diameter individual five–petal bright yellow flowers which are held above the foliage to good advantage. The flower show begins in late spring and continues until frost. This profusion of yellow flowers is the source of the numerous common names referencing yellow or gold, such as Rain–Of–Gold, Shower–Of–Gold, Spray–Of–Gold, or Yellow Plumbago.
Thyrallis can be grown on a range of soil types with good drainage and an acidic to slightly alkaline pH. Flowering is best in full sun, but plants will remain reasonably dense and have some flowers in partial shade. Heat tolerance in thyrallis is outstanding and plants are moderately drought tolerant once established. Spider mites and caterpillars can be occasional pests, but seldom require control measures. Softwood to semi–hard wood cuttings can readily be rooted during warm weather. Rooting appears to be a bit trickier in cooler weather.
The genus name Galphimia is an anagram of the closely related genus Malpighia (which contains Malpighia glabra or the Barbados Cherry). There is some confusion over the correct taxonomic classification of this species, once listed as Thyrallis glauca (this is where the common name of thyrallis derives), it has since been determined that the valid scientific name is Galphimia glauca. Still others contend that many of the plants in the U.S. nursery trade are really Galphimia gracilis, however since G. gracilis may be a synonym of G. glauca, it may be a moot point. Regardless of the taxonomic argument among academics, the fact remains that this promising species has a bright future for Texas gardens! Thyrallis is an excellent addition to the Texas SuperStar® family and our regional plant palette.
Prepared by Michael A. Arnold, 4/24/08