Perennial vegetables are an enduring lot. Many are capable of surviving drought, recurring cold, deep shade and short periods of flooding.

FILE 2003/Staff photo

Rhubarb stems are OK, but don't try to eat the leaves or roots - they're poisonous.

Some even have developed natural defenses for discouraging predators. But those chemical and physical barriers mean people should proceed with caution, particularly when sampling new food plants, said Eric Toensmeier, author of Perennial Vegetables: From Artichoke to Zuiki Taro, a Gardener's Guide to Over 100 Delicious, Easy-to-Grow Edibles (Chelsea Green Publishing, $35).

"Make sure to prepare the food properly," Mr. Toensmeier said. "Some vegetables are toxic when raw but quite healthy to eat when sufficiently cooked. Also, make sure you are eating the proper part of the plant."

Some plant-specific warnings:

STINGING NETTLES. Initial impressions aside, nettles are excellent for eating when boiled, Mr. Toensmeier said. They're among the very first of the green vegetables to emerge in spring, often while snow is on the ground.

"Nettles are probably more appreciated by diners outside the United States," he said. "They're considered a gourmet plant in Italy. But you've got to pick them with gloves on. They're covered with stinging hairs that work like little syringes, injecting a painful mix of chemicals including formic acid. Nettles need this defense because their leaves are so nutritious."

BRACKEN FERN. Fiddleheads or the coiled young fronds of many ferns are edible, but those of the bracken variety (Pteridium aquilinum) have been linked with stomach cancer and probably should be avoided, Mr. Toensmeier said.

WATER PARSNIP. This is an aquatic wild edible valued for the taste of its roots. "Unfortunately, it is very difficult to distinguish water parsnip from the deadly water hemlock, and so I recommend that only experienced botanists experiment with this plant," Mr. Toensmeier said.

CACTUS PADS. Cactus is a popular edible plant in Mexico, where they were domesticated some 9,000 years ago. They've become three times as widely grown there as carrots, Mr. Toensmeier said, and have become an important commercial crop, especially the sweet fruits (tunas) of some Opuntia cacti.

The pads of many prickly pear cacti are covered with spines, however, making them a challenge to harvest and cook. Even some of the spineless varieties grow bulges called glochids. Their tiny hairs can cause itching and irritation for days, he said. Wear leather gloves and peel them as you would a cucumber. Rinse well to ensure all the spines and glochids have been removed.

RHUBARB. The leaves and roots of rhubarb are poisonous, capable of causing nausea, dizziness, convulsions and possibly death. Leaf stalks are the edible portions of this popular fruitlike vegetable, but only after they've been cooked and only when served in moderate amounts. "Make sure to train any children who might be in your garden to avoid eating anything but the stalks of rhubarb," Mr. Toensmeier said. "The stalks contain only the relatively harmless oxalic acid."

People have eaten perennial vegetables for centuries, Mr. Toensmeier said. "They're usually easier to grow but often harder to harvest and process. Just use a bit of common sense when cooking some of these new plants for yourself, or when serving them to your friends who have never tried them before."