Perennials That Emit a Milky Sap

Perennials of several families emit milky sap from their cut stems, roots or leaves. The best known may be milkweeds, of the Asclepiadaceae family. Milkweed plants have varying degrees of toxicity, notes the Purdue University School of Veterinary Medicine. Other milky-sapped plants may cause toxic reactions, including skin and eye irritation. Many of them, however, are more dangerous to animals than to people.

Dogbane, or Apocynum cannabinum, is a 3- to 4-foot perennial found in all 50 U.S. states. It closely resembles milkweed plants, but belongs to the Apocynaceae family. Dogbane's broken red stems release milky, white sap with skin-irritating glycosides. Its roots contain the heart stimulant cymarin. This perennial has large, lancelike or oval green leaves. Clusters of small, cup-shaped white flowers top the stems in late spring and summer. String-beanlike seedpods follow the blooms. Dogbane is common along river and stream banks, in wet ditches and in cultivated fields.

Their brilliant red, elegant pink or creamy white colors have made perennial poinsettia plants, or Euphorbia pulcherrima, decorative staples during the year-end holidays. Poinsettias, however, contain milky, white sap with toxic diterpene esters. These toxins may cause nausea and oral discomfort. Degree of toxicity, however, may differ among poinsettia varieties. It may also depend on the sensitivity of the person or animal exposed to the sap. Wearing protective clothing and sealing cut stems with a burning match when using them in fresh floral designs prevents accidental skin exposure. Keeping poinsettias away from young children and pets reduces the risk of ingestion.

Perennial Arkansas, or blue star, amsonia, scientifically known as Amsonia hubrichtii, shares the milky, white sap of other dogbane family plants. A benefit of the sap, however, is that deer tend avoid the Perennial Plant Association's 2011 Perennial Plant of the Year. The 3-foot high and wide plant has feathery, bright green, spring and summer foliage that becomes brilliant yellow in autumn. Rounded spikes of dense, star-shaped flowers top its stems in spring.

Common catsear, or flatweed, or Hypochoeris radicata, is a daisy family perennial native to Asia, Europe and North Africa. It has now spread across the eastern and Pacific Northwestern United States, reports the the Ohio State University Perennial and Biennial Weed guide. The dandelionlike plant has a basal clump of long, narrow lobed green leaves. Yellow flowerheads – up to 1 1/2 inches across – crown its slender stems. They normally appear after September. The blooms give way to plumed seedpods. Horses ingesting this perennial's milky sap may develop stringhalt, or spastic hindquarters.