WOODSTOCK, Va. -- Esther Miller is here to warn you about being blistered by the milk of horticultural kindness -- in her case, by brushing up against the creamy sap oozing from plants belonging to the family Euphorbia.

This is a varied and extensive plant group that includes such holiday favorites as poinsettias (Euphorbia pulcherrima) and crown of thorns (Euphorbia splendens).

"A friend came over for some plants I had and wondered if I had anything that would root easily," said Miller, a master gardener who lives on a farm near this historic Shenandoah Valley community. "I said, 'Sure, try this.' I had stuck it under a rock in this wall and it grew like crazy.

"But I didn't have my pruners with me, so I broke off a couple of stems for her and had a tough time doing it. The stems were fibrous and leaked a nasty, white sticky sap. I commented that it didn't look good and we both agreed I'd better scrub it off pretty thoroughly. But we had a few other things to do and it was 10 to 15 minutes before I got into the house."

The sap had dried to a latex-like sheen on her skin, so she cleaned the affected area using liberal amounts of soap and warm water. "I made the really big mistake of forgetting about it. For maybe all of an hour." Then her eyes started burning and she felt a hot streak building around the corners of her mouth.

That prompted her to call a fellow master gardener, who had taught horticulture for more than 20 years, to see whether they could determine what was causing the inflammation. They agreed it was a euphorb, probably a myrsinites: a blue-green succulent that thrives in crevices and rock walls. It is called variably "creeping spurge," "myrtle spurge" or "donkey tail spurge."

The low-lying varietal can survive poor soils and drought, which has earned it a merit award from Britain's Royal Horticultural Society. But it also can be invasive, notably in the American West, where several states have labeled it a noxious weed.

Once Miller was satisfied that she had identified the plant, she went to bed hoping for the best. But by morning, her face and nose were so swollen she had trouble putting on her glasses.

She spent three hours in a hospital emergency room, where she was treated with anti-inflammatories and antibiotics, reducing the swelling and relieving most of the pain. The redness on her skin went away, although it took more than two weeks for the blisters and crusty patches to disappear.

"It just never occurred to me that a plain little plant could cause so much trouble," Miller said.

Poisonous plants are a particular problem during the holidays, when people unknowingly exchange them as gifts or bring them inside for Yule-time decorating. Flower selections frequently include poinsettias, which commonly and mistakenly are labeled poisonous.

"Poinsettias are often thought of as one of the most dangerous holiday plants, but research has found that a 50-pound child would have to eat 500 to 600 leaves to be affected," said Ward Upham, extension associate and master gardener coordinator at Kansas State University. "The berries on a mistletoe are more of a threat and can be fatal if enough are eaten."

Poinsettias should not be excused from the problem plant list, though. They can cause allergic reactions, stomach discomfort and nausea in certain people. It would be wise to ask prospective guests about any particular plant sensitivities.

Plants toxic to humans frequently can be poisonous to pets, too, and often to a greater degree.

"Think chocolate (derived from cacao tree nuts) with dogs," Upham said. "We can ingest it OK, but pets are smaller in size than humans. A small amount can cause toxicity."

Other familiar holiday plants posing potential problems include the Star of Bethlehem, and Easter and tiger lilies. The Star of Bethlehem may lead to heart problems, and the lilies can cause renal and kidney damage, Kansas State horticulturists say.

Other plants to be wary of at any time of year include mums, lilies of the valley, hyacinth, daffodils and philodendron. "These are potted plants that are usually kept outdoors, but are often brought indoors during the cold winter months," Upham said.

The moral of the story is to beware of any growing thing that displays a milky sap.

"Scrub it vigorously if you do get it on you, and then use some alcohol to get it thoroughly off," Miller said. "And for gosh sakes, don't put your fingers anywhere near your face unless you're sure the sap is all gone."

One final suggestion: "Don't be afraid of (the) Latin names of plants. The only way the doctors knew what to do for me was to Google the name of the plant and see what it could do to me, then research the proper treatment."

Recommended reading:

"Know Your Poisonous Plants," By Wilma Roberts James. Naturegraph Publishers. List price: $9.95.

On the Net:

For more about plants toxic to humans, see this Texas A&M Web site: http://plantanswers.tamu.edu/publications/poison/poison.html; for information about plants poisonous to people, livestock and pets, look to the Cornell University Poisonous Plants Informational Database: http://www.ansci.cornell.edu/plants/anispecies.html.

You can contact Dean Fosdick at deanfosdick(at)netscape.net.