Great year for large-flowered foxglove in the oak savannas

Large-flowered false foxglove (Aureolaria grandiflora) is one of the great members of the oak savanna flora. Its savanna dependence derives from its absolute requirement for parasitism on roots of members of the white oak group (white and bur oak). It is generally fairly showy but this year populations are especially lush. In Unit 10, where the oaks are primarily burs, there are large populations.

We first established this species at Pleasant Valley Conservancy about 10 years ago, planting seeds under the drip lines of the oaks. Within two-three years small populations of flowering plants had developed, and they have gradually spread across the savanna areas.

This species is a member of the Orobanchaceae family (formerly Scrophulariaceae), a group with a number of hemiparasitic species. In addition to Aureolaria, genera in our area that are hemiparasitic include Agalinis and Castilleja (Indian paintbrush).

According to research done by Musselman (American Midland Naturalist, Vol. 82, July 1969), seeds of Aureolaria germinate normally and start to form seedlings, but unless they parasitize an oak rootlet they seldom get past the cotyledon stage before dying. 

Although Aureolaria grandiflora is an obligate parasite on oaks, it does not do any harm to the tree. It primarily "infects" the tiny roots that are present under the drip line of the canopy. 

The especially prolific growth this year is probably linked with the unusual summer weather we have been having (fairly cool and good rainfall).