Garden Detective: Mystery plant could be cobra lily

This year and never before, I have had a lily-type of plant sprouting up all over my yard. I do not know where they came from. There are tiny plants all over my yard, even coming up through my ground cover.

When I pull up the very small plant, it is shallow rooted but if I let it grow it breaks off leaving the root (or bulb) in the soil. I have let a couple grow and in general they are very attractive. They bloom just like a lily but I do not know if it is poisonous or invasive.

The other light green spread of plants seemed to come up overnight. The plant looks like the foliage that a potato might send up but I do not stick potatoes or peels in the ground because I know they can sprout. They are very easy to pull up. Any ideas about my mysterious invader plants?

Carol Rose, Woodland

Thanks for sharing your mystery flower. Judging from your photos, it looks like a cobra lily or Jack-in-the-Pulpit, two common names for varieties of Arisaema. This genus has about 260 species, native to Asia, Africa and parts of North America. In recent years, many species have been imported from China for use in home gardens.

These are unusual and eye-catching “flowers.” The central spike is called a spadix. It is surrounded by a hoodlike spathe that forms the “flower.” The actual flowers are tucked way down inside the funnel. That’s also where the red-orange berries form.

These distinctive plants are part of the Aroid family, sometimes called the Philodendron or Arum family. This family also includes such popular plants as anthurium, elephant ear and monstera.

We sent your photo to Wilbert Hetterscheid, a Dutch plant expert and main “aroider” of the International Aroid Society. He solved the mystery. It’s not an Arisaema, but an Arum.

“That is a true Arum species, more specificly Arum hygrophilum,” he said.

Its nickname is Streambank Arum, because that’s where it likes to grow. That species is native to Israel and Syria, but has become popular in European gardens, too.

The next question: How did it get here?

“Possibly it came with compost?” suggested Hetterscheid. “Or some very unhappy bird had a massive diarrhea after eating the berries of this species, although it is not supposed to be native to the USA.”

According to UC master gardeners, Arums are not true lilies but herbaceous perennials that form bulblike corms. The plants contain high amounts of oxalic acid, so don’t eat them; oxalic acid is poisonous. Because they spread so easily through seed and grow so rapidly, these plants are considered invasive in many parts of the world, especially along waterways. Once they take over a yard, they can be hard to contain. They thrive in moist areas with some shade. These plants will die back in the winter, but resprout next spring.

To control, pull out the new sprouts as they emerge. Wear gloves when handling these plants to avoid skin irritation.