Tom's Blog

Saturday, August 7, 2010

Large-flowered false foxglove doing very well in the savannas

Large-flowered false foxglove (Aureolaria grandiflora) is a savanna specialist with an interesting life history. This year it is doing particularly well at Pleasant Valley Conservancy, probably because of the very good moisture levels.

This species is called a hemiparasite, which means that it grows only in association with another species, not killing it, but getting important nutrients from it. In contrast to a true parasite, it has chlorophyll and carries out photosynthesis. However, its roots must set up an infection with another plant in order to survive. In the case of A. grandiflora, the required host is an oak, specifically a member of the white oak group (bur, white, swamp white).

If you plant seeds of this species in potting soil and try to cultivate the plant in a greenhouse, the seeds germinate and make tiny plants, but unless they set up an association with an oak, they do not develop. Eventually they die. Note that this is an "obligate" parasitism. There is no evidence that the foxglove benefits the oak.

When we started oak savanna restoration at Pleasant Valley Conservancy, this species was not present, but Rich Henderson kindly gave us some seed. "Plant them under the drip line of the oaks," Rich told us, and this is what we did. We walked around the savanna with the bag of seed, looking up at the canopy for a large oak. Then we walked around the periphery of the tree, throwing out seeds. Within a couple of years, we had our first plants, and they have spread greatly on their own.

Whenever I see a population of this foxglove, I always look to see if there is an oak nearby. Sometimes the only tree nearby is a small oak grub, but the population in the photos here was growing with a nice large white oak. As the photo at the top shows, this population is very healthy.

The flowers are quite substantial and this species would make an excellent garden plant, provided you had an oak nearby.

This genus is in the Snapdragon family (Scrophulariaceae), and it turns out that quite a few members of this family are hemiparasites. For instance, wood betony and lousewort (Pedicularis canadensis and P. lanceolata) are also snapdragons and are well known hemiparasites. Indian paintbrush is another.

I did a literature search and could find no research dealing with the details of Aureolaria hemiparasitism, although there has been work with paintbrush.


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