Page 904 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

Poisonous Plants of the United States Chapter | 61 859

VetBooks.ir TABLE 61.5 Water Hemlock Species and Geographical Distribution Geographical Distribution

Species
C. bulbifera Northern U.S., southern Canada
C. bolanderi Central to western CA
C. californica Central to western CA
C. douglasii Throughout U.S.
C. machenziana Southeastern AK north to the Brooks Range
C. occidentalis Rocky Mountains, Black Hills, WA; south into NV and NM
C. vagans Pacific Northwest U.S. and Canada

Distribution three pinnately divided may be 30 60 cm long. Flowers
are small, white or cream colored, and in terminal
There are approximately 20 species of Cicuta throughout
umbrella-shaped clusters. The fruits are small, with promi-
the world, and all are poisonous. Most of these species
nent ribs, and encased in a hard brownish shell very similar
are found in North America; nine are common in the
to those of poison hemlock. The primary distinguishing
United States, and seven are found in the western United
feature separating water and poison hemlock is the tuber-
States (Table 61.5).
ous roots with the very distinct partitions in water hemlock
(Figure 61.6). Poison hemlock lacks the large tubers,
Description although occasionally there are very small partitions
observed in the area where the root and stem connect if the
Water hemlock is often confused with poison hemlock; in
plant is cut vertically. The parsnip-like root is a single tap-
fact, there are similar plant characteristics and both belong
root in poison hemlock, whereas there are often multiple
to the Umbelliferae family (Figure 61.6). However, their
white parsnip-like roots radiating off the main tubers in
toxic effects are dramatically different, and when toxicoses
water hemlock (Figure 61.6).
occur, differentiation between the two genera is important.
OH

HO CH 2 CH CH C C C C CH CH CH CH CH CHCHC H
2
3 7
2
(8)
Cicutoxin
Water hemlock (Cicuta) is a biennial, 1 or 2 m tall, Toxicology
with thickened tubers possessing long, slender parsnip-like
The toxic principle in water hemlock is a long-chain, highly
roots radiating out from the main tuber. Water hemlock
unsaturated alcohol called cicutoxin. Water hemlock acts on
frequently grows directly in streambeds or water sources
the central nervous system as a stimulant, inducing violent
and is limited to wet habitats. The tubers are bulbous and
grand mal seizures and death from respiratory failure.
exhibit several chambers or cavities separated by cross-
Tubers are the most toxic part of the plant, especially in
partitions as seen in a vertical cut through the tuber at the
early spring. The parsnip-like roots extending from the tuber
base of the stem. The cut surface of the stem or tuber
are two to four times less toxic, and as the vegetative parts
exudes a yellowish, thick, oily liquid believed to be pre-
of the plant grow and mature, they become less toxic.
dominantly cicutoxin (8).Thisoily substance has a
Preliminary studies suggest that mature leaves and stems are
parsnip-like odor. The chambered tuber is a distinguishing
much less toxic and after drying are non-toxic (Panter et al.,
feature of this plant (Figure 61.6). The roots extending
1988). Historically, water hemlock was believed to be most
from the tuber may be solid, white, and fleshy, closely
dangerous in early spring, and poisoning usually occurred
resembling a parsnip. The stems are hollow except at the
when animals milled around in streambeds or sloughs and
nodes, hairless, and occasionally have purple stripes up the
exposed tubers, which were then ingested. Although this is
stem. Leaf stalks alternate up the stem and leaves two or