Tom's Blog

Thursday, July 28, 2011

Giant false foxglove, a hemiparasite, now starting to bloom

One of the more fascinating savanna forbs is Giant False Foxglove (Aureolaria grandiflora), a member of the Snapdragon (Scrophulariaceae) family that lives hemiparastically on oak roots. The photo here, taken by Kathie, is of the earliest flower seen this year.

There are quite a few members of the Snapdragon family that grow hemiparastically on other species, including wood betany, lousewort, and Indian paintbrush. These plants are called hemiparasites because even though they suck up nutrients from their host plants, they also have an additional extensive root system that helps support the plant. The parasitic action results when small structures called haustoria grow into the host roots where enlarged bulbous structures are formed.

Although most of the host plants of hemiparasites are grasses or forbs, A. grandiflora is especially interesting because its host is the oak tree. (The species of oak is not critical.)

At Pleasant Valley Conservancy we first spread seed of A. grandiflora about 10 years ago. The technique was to sow seed in a circle around the drip line of an oak tree. This is an area where the oak tree has an extensive root system near the surface. Some of the germinating seeds send down roots and connect with the host plant. It may take several years for development to reach the point of flowering, but once it does, A. grandiflora is able set up a perennial existence. (There is another species, A. pedicularia, that is only an annual.)

We tried to raise A. grandiflora from seed in the greenhouse. The seeds germinated well and started to form tiny plants, but without hosts they stopped growing and eventually died. This plant is interesting from an evolutionary viewpoint.

Once A. grandiflora became established, we were able to collect seeds locally and spread them further. We now have well established colonies in most of the savanna areas at Pleasant Valley Conservancy.


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