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Monday - March 16, 2009

From: Wimberley, TX
Region: Southwest
Topic: Poisonous Plants
Title: Do prairie verbenas (Glandularia bipinnatifida) have toxic sap?
Answered by: Nan Hampton and Jimmy Mills

QUESTION:

Dear Mr. Smarty Plants, I live in Wimberley, TX and my 6 year old daughter picked wildflowers for her Mom over the weekend. I believe the species was Prairie Verbena but not 100% certain. Now, four days later her fingers (index, middle and thumb) have several blisters on them (similar to a poison ivy reaction). Went to Doctor and he could not pinpoint the cause. I am pretty certain she did not get into poison ivy. My question is.. is the "sap" from the stem of this wildflower indicative of causing allergic skin reactions? If not, do you know of any Central Texas native wildflower, other than the various poison ivy species, that could cause such a skin reaction (as I am not certain the flower she picked was indeed the Praire Verbena)? Thank you for your assistance.

ANSWER:

I can find no evidence in my favorite Toxic Plant databases (Poisonous Plants of North Carolina, Cornell University Plants Poisonous to Livestock, Canadian Poisonous Plants Information System, University of Pennsylvania Poisonous Plants, Texas Toxic Plant Database, or University of California-Davis Toxic Plants) that Glandularia bipinnatifida var. bipinnatifida (prairie verbena) causes dermatitis or is any other way toxic. Of course, there is always the possibility that your daughter might have a unique allergy to the sap.

Delena Tull in Edible and Useful Plants of Texas and the Southwest , pp. 298-301, has a thorough discussion of "Irritant Dermatitis".

There are several plants that occur in the Central Texas area that can cause dermatitis of some sort. First, there are the Tragia spp. that have 4 representatives in the area: Tragia betonicifolia (betonyleaf noseburn), Tragia brevispica (shortspike noseburn), Tragia nigricans (dark noseburn) and Tragia ramosa (branched noseburn) and there are also stinging nettles such as Urtica chamaedryoides (heartleaf nettle) and Cnidoscolus texanus (Texas bullnettle). However, these plants would have caused an immediate stinging sensation that your daughter would have told you about. Having been "stung" by all of the above, we can tell you they are unpleasant.

There are several other plant families that have irritating sap. The Family Ranunculaceae (buttercup family) has several members with irritating sap. The clematis vines are in that family and are named by Tull as having "highly caustic, acrid juices". The following are the clematis species that occur in Central Texas: Clematis drummondii (Drummond's clematis), Clematis pitcheri (bluebill), and Clematis texensis (scarlet leather flower). Euphorbia bicolor (snow on the prairie) and Euphorbia marginata (snow on the mountain), both in the Family Euphorbiaceae (Spurge Family) are two other plants that are common in Central Texas that Tull says have irritating sap that can blister the skin. Please see Tull's book for a discussion for other plant irritants that might not be as commonly encountered in our area.

For an explanation of the blisters appearing on your daughter's fingers, Mr. Smarty Plants has thought of several other possibilities:

1. Perhaps there was a small Toxicodendron radicans (eastern poison ivy) growing in or near the verbenas that you didn't see that your daughter happened to touch. Or, perhaps some small animal walked through a patch of poison ivy and got the oil on its fur and then walked through the verbenas before your daughter picked them—a rather remote chance, we realize, but not completely out of the realm of possibility. Many people have gotten poison ivy from petting their dog after it made a foray through the poison ivy!

2. Stings from from fire ants (Solenopsis spp.) can cause blisters; but, again, your daughter would have noticed being stung by fire ants and let you know about it.

3. Other insects, such as blister beetles (Family Meloidae), can cause dermatitis and blisters.

Bibliography

Edible and Useful Plants of Texas and the Southwest: Including recipes, harmful plants, natural dyes, and textile fibers: A Practical Guide (1999) Tull, D.

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