Hold the Parsnips- Toxic Plants of the Parsley Family

Giant Hogwood, a plant causing severe dermatitus merely from touching it.

Giant Hogweed, a plant causing severe dermatitus merely from brushing against it. Photo by Fritz Geller-Grimm

HOLD THE PARSNIPS

That similar-looking plants can either nourish us or kill us might seem like a cruel trick of nature but is more likely an outcome of evolutionary forces acting on genes. There’s no better example than the carrot family  (known to botanists as the Apiaceae, and previously  and, to some still, the Umbelliferae) which comprises a host of species both toxic and edible that are in some cases easily confused by the unwary.  Included in the family is Daucus carota the well-known Queen’s Anne Lace that blankets unused fields and charms the eye but is also regarded as a pernicious weed. It bears a quite inedible taproot. Yet from this same species is derived our beloved carrot thanks to artificial selection by hungry humans over centuries. Beyond their roots, their relationship would be obvious if the carrot were left to flower and go to seed. Both display  divided leaves and similar flat-topped clusters of small flowers (in most species white) followed by  distinctive winged fruits.  Within the flower is the most characteristic family feature- the style which has a swollen base that secretes nectar.

The overwhelming majority of species in the family (there are 2500 to 3000 species world-wide), of course, are wild, mostly occurring, with exceptions, as temperate zone herbs. Many of these species occur in wetlands and within this group are a small group of tall and coarse herbs that are dangerously toxic to humans. Some are very similar in appearance to harmless or even edible species and this confusion has led to tragic outcomes for humans. The toxic species discussed here are widely distributed and, in suitable habitat, common in temperate North America or in Europe. They belong to three genera- Cicuta, Conium and Heracleum, which are described briefly below along with several other look-alike species.

 The common names for these species are often as confusing as the plants themselves, underscoring the need to use scientific nomenclature when possible. “Parsnip” has long been applied to several species, poisonous or not. Furthermore, members of two genera (Cicuta and Conium) share the common name “hemlock” but the plants are not at all related to the hemlock tree (Tsuga canadensis).  

In Cicuta (the water hemlocks)  and Conium (poison hemlock)  ingestion precedes poisoning. In Heracleum, skin contact of any part of the plant leads to severe dermatitis. The  toxic alkaloid (see below for more on alkaloids) in  Cicuta directly attacks the central nervous system. In Conium gradual paralysis sets in while the victim is conscious. Convulsions are typical of water hemlock poisonings, atypical of poison hemlock. Unfortunately, ingestion of parts of plants from the “hemlock” genera continues to be common.  More than 63,000 calls were made to medical centers annually, mostly involving children as reported in 2012  at the Medscape web-site.   Note that the brief descriptions given below are not intended to provide a basis for identifying species or determining  edibility. Consult other web-sites or specialists for these details.

Cicuta spp- (the water-hemlocks)

The main poisonous principle in the water-hemlocks is a resiny alkaloid called cicutine. Other toxic but less concentrated alkaloids also are present in the plant. There are several species in the genus:

C. maculata (water-hemlock) grows wild from eastern Canada to the southern Appalachians west to Texas and the Dakotas. C. maculata, like related species, has a hollow stem and sub-divided leaves somewhat resembling a fern. It may reach 2.4 m (8’) in height. Small white flowers are aggregated into flat-topped clusters as is typical of the family. Its roots (actually fleshy, finger-like tubers extending out from the base of the stem) smell and taste like parsnips and resemble wild parsnips (Pastinaca sativa) roots which are edible and often grow in the same habitat. A lethal dose can result from eating a single tuber of water-hemlock. As little as a 2 cm (0.8”) section of the root can produce fatal results in children and perhaps adults. The use of a stem as a toy whistle was fatal to a child.  

Flowers of Cicuta maculata, water-hemlock. From Iowa State Extension Service

Flowers of Cicuta maculata, water-hemlock. From Iowa State Extension Service

C. mexicana is similar to C. maculata with broader leaves and somewhat coarser stature. Some authorities consider this species to be only a sub-species of C. maculata.  Despite its species epithet, C. mexicana  is found in wetland habitats of the southeastern United States west to Texas and eastern Mexico. Toxicity of C. mexicana equals that of C. maculata.

Water-hemlock roots. From Iowa State Extension Service

Water-hemlock roots. From Iowa State Extension Service

Cicuta douglasii– Western Water Hemlock; native from the Rocky Mountains to Alaska and California.  Cicutoxin  is concentrated in the chambered rootstock but also occurs in the leaves and stems.  All parts are highly toxic to humans and to livestock. This species’ foliage is fragrant, and because it appears early in spring may be tempting  to livestock at that time. The oil coating a single bulb is enough to kill a 1600 pound cow.

C. bulbifera– a strictly wetland species with leaves narrower than other Cicutas and smaller in stature. Primarily reproduces by small bulblets in leaf axils rather than by seed. Found in shallow water and swamps throughout temperate North America. Presumably as poisonous as C. maculata.

C. virosa a European species now found through much of Canada and Alaska. It has been responsible for human fatalities in Europe.

Conium

An illustration of Conium maculatum from an 1885 book by O. W. Thome'

An illustration of Conium maculatum from an 1885 book by O. W. Thome’

Conium maculata  (poison hemlock) is a biennial or perennial Eurasian species originally introduced as a garden plant in the U.S. which has since become established in most of North America, less so in the southern states. Its coarse stems are spotted with purplish blotches and its leaves are finely dissected and fern-like suggesting parsley. It can be 3 m ( 10’) tall. The lethal properties of poison-hemlock have long been known and a potion made from its roots presumably was taken by Socrates to commit suicide. The poisonous alkaloid coniine is found in all tissues of the plants but concentrated in the seeds. There are additional toxic compounds associated with coniine in the plant. Coniine affects humans similarly to nicotine but at a much more intense level. There is an initial stimulation which is followed by nervous system depression, leading to paralysis and death if not flushed out of the body.  The presence of coniine in poison hemlock results in a very pungent foul odor when the plant is cut or damaged. This may serve as a characteristic that differentiates it from other species and also might discourage some from ingesting parts of the plant.

Heracleum

Heracleum mantegazzianum–  (Giant Hogweed) is native to the Caucasus and southwest Asia. It was introduced into New York state in 1917, and has presently escaped to 16 states in the Northeastern United States plus Illinois, Oregon and Washington state. It’s also found in eastern Canada, British Columbia and Alaska. The plant is occasionally planted as a yard ornamental in recognition of its impressive size, however it is on the noxious plant list of some states (e.g., Ohio) making it unlawful to propagate, sell or transport. The plant is huge, reaching 5 m (17’) height although often living only a few years and sometimes flowering only once. All parts of the plant are poisonous if ingested or even touched, as the sap contains furanocoumarins which in the presence of sunlight cause severe and long-lasting dermatitis. A second Old World species, H. sphondylium, is similar to H. maximum (below) both in size and relative innocuousness. It is naturalized in the northeast U.S. and eastern Canada. In Europe it has been eaten as a vegetable in the northern countries and in Russia. For a little more on giant hogweed see the article entitled ‘Hold the Parsnips-Update on the Giant Hogweed’.

North America also has a native Heracleum- H. maximum, which bears the common name cow-parsnip and occurs in meadows, stream banks, alluvial thickets and moist forests from Newfoundland to Alaska  south to New Mexico and east to the southern Appalachians. Rather foul smelling, this common perennial can reach 3 m in height with hollow, wooly stems and leaves thrice-compound below and undivided (but lobed) higher up. Interestingly this species has a history of edibility as discovered by native Americans and confirmed by curious naturalists, but its foul odor convinces most to discard the first boil-water before tasting. Young leaf stalks are reportedly agreeable or even delicious after boiling in two waters (Fernald et al. 1958). 

The native Heracleum maximum. Photo by Pete Curtis, Univ. Minnesota

The native Heracleum maximum. Photo by Pete Curtis, Univ. Minnesota

Pastinaca sativa, originally from Europe, is a biennial weed often found in roadsides and waste areas in our northern states. Cultivated strains of this species are available in markets as the familiar root crop. Flowers are yellow and the stem grooved. Like water hemlock, this plant is known as wild parsnips. But unlike plants of the genus Cicuta, Pastinaca is, much less toxic, i.e., it’s toxic potential is limited to photodermatitis but to a lesser degree than the giant hogweed, and the roots are edible.

The distinctive yellow flowers of Pastinaca sativa. www.florafinder.com

The distinctive yellow flowers of Pastinaca sativa. http://www.florafinder.com

All Pastinaca plants, including the commercial crop, must be handled so as to avoid contacting the sap. A careless forager could confuse roots of Pastinaca with those of Cicuta, leading to a sad end if the roots proved tempting to eat.

The roots of  Pastinaca sativa

The roots of Pastinaca sativa

Sium suave (water or swamp parsnip)- an aquatic perennial native to North America, 1-2 m tall with leaves that are only once-compound. Although regarded as a non-toxic species that produces an edible root, it  shares similar marsh habitats with the Cicuta species and therefore strong caution is needed if consumption is planned. In fact, Fernald et al (1958) suggest feeding a sample to a rabbit or guinea pig before proceeding! Consult www. agf.gov.bc.ca/cropprot/whemlock.htm  for photographs comparing Sium to C. douglasii.

Alkaloids

The toxic principle in most of the poisonous  plants discussed above and in many other plants are called alkaloids (the dermatitis caused by Heracleum is due to a furanocoumarin, ). The thousands of alkaloids are all naturally occurring organic nitrogen-containing bases having an aromatic or ring structure. Examples are strychnine, morphine, nicotine and caffeine but more than 3000 are known, many toxic to man. Alkaloids are predominately synthesized by vascular plants and over 4000 plant species are known to produce them. A few fungi and animals also synthesize alkaloids. They are basic or alkaline in reaction rather than acidic and combine with acids to form salts.

The function of alkaloids in plants is mostly unknown. Some appear to be merely metabolic by-products while others are suspected to be plant defenses that repel animal predators. In some plants, alkaloid concentrations increase just before seed formation and then decline when the seed is ripe, suggesting a role for the alkaloids in seed production. Capsaicin, an alkaloid that gives hot peppers seeds their “heat”, has been shown to repel mammals yet go undetected by birds which consume the seeds and later void them still viable, thus acting as dispersal agents. Coniine, the deadly alkaloid in Conium, also is found in the pitcher plant (Sarracenia flava), one of the well-known carnivorous plants native to swamps and bogs in the southeastern United States.  The alkaloid stuns the insects which are attracted to the plant’s sugars rendering them more susceptible to the slow dissolution that occurs in the small pool of liquid at the base of the trumpet-shaped leaf.  

Furanocoumarins, which are not alkaloids, occur not only in giant hogweed, but in lesser concentrations  in other genera in the Apiaceae such as Angelica and Zizia.  However plants from both these genera are considered edible by humans. Nevertheless one report concluded that furanocoumarins repel herbivores of several kinds ranging from insects to mammals. It seems likely that further research will define an expanding role for the toxic compounds found in many members of the carrot family.

 A few of the many sources consulted follow.

agf.gov.bc.ca/cropprot/whemlock.htm 

ars.usda.gov/Services/docs.htm?docid=9996

emedicine.medscape.com/article/821362-overview

Fernald, M. L., A.C. Kinsey and R. C. Rollins 1958.  Edible Wild Plants of Eastern North America. Harper & Bros.,  Pub. New York.

henriettesherbal.com/eclectic/usdisp/cicuta.html

seagrant.sunysb.edu/ais/pdfs/GiantHogweedFactSheet.pdf

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