Description: This adventive perennial plant is about
½–2½' tall, branching occasionally. The light green stems
are hairless and more or less ribbed; they are more or less erect, but
occasionally sprawl. The alternate compound leaves are oddly pinnate (simple or
double), often with a ternary arrangement of leaflets
(usually in groups of 3, but sometimes in groups of 5 or more). In outline, a
compound leaf is triangular, broader at the base than at its tip, its size up
to 12" long and 8" across. Each leaflet is ovate, ovate-lanceolate, or
ovate-oblanceolate, and about 1" long and ½" across. Usually the
terminal leaflet has a short petiole, while the lateral leaflets are sessile.
The margin of each leaflet is coarsely dentate, sometimes with 1 or 2 lobes
that are cleft. Its base can be wedge-shaped or rounded and asymmetric. The
petioles of the compound leaves are rather long and stout; there is a
membranous sheath where the base of each petiole joins the stem. The foliage of
Pacific Water Parsley is hairless. Occasionally, some of the upper stems will
bolt and produce compound umbels of small white flowers; these umbels are
flat-headed at the top. Each compound umbel is about 3" across when fully
developed, and consists of about 8-12 umbellets. Each umbellet has about 8-12
small white flowers that are individually about 1/8" across. There are about
8-12 bractlets underneath each umbellet; they green, linear, and spread
outward. At the base of each compound umbel, there are 2 or more bracts that
have an appearance that is similar to the bractlets, except they are larger in
size. Each flower has 5 notched white petals, 5 white stamens, and a central
pistil. The blooming period (in Illinois) occurs from mid-summer to early fall,
and lasts about 1-2 months. The compound umbels of flowers are produced
sparingly during this time period. Each flower is replaced by a single
elongated seed. The root system consists of fibrous roots and slender white
runners that lie slightly below the ground surface. This plant often forms
colonies.
Cultivation: The
preference is full sun to light shade, wet conditions, and fertile soil. This
plant flourishes in wet mucky soil or shallow water, and is semi-aquatic. In
situations with little sun, fewer flowers will be produced. This plant can
spread aggressively in wetland areas.
Range
& Habitat: Apparently, Pacific Water Parsley has not naturalized
within the state in the past, although several colonies of this species have
been discovered recently in Champaign County, Illinois (see
Distribution
Map). These colonies were growing along a small stream with slow-moving
water; some of the plants were growing in shallow water. It is likely that this
species can thrive in other types of wetlands. This species is native to the
Pacific Northwest from California to Alaska, where it occurs along rivers,
marshes, and fens. Recently, it has been used as an adaptable wetland species
by the horticultural industry. Unfortunately, Pacific Water Parsley appears to
be aggressive and it will probably spread into new areas in the
future.
Faunal
Associations: Like other members of the Carrot family, the flowers
attract small bees, flies, wasps, and other insects. The caterpillars of the
butterfly Papilio polyxenes asterias (Black Swallowtail) can probably
feed on the foliage, as the caterpillars of similar Swallowtail butterflies in
the Pacific Northwest are known to feed on the foliage of this species. While
growing in water, this plant provides cover for aquatic insects and small fish.
It is unclear whether or not the foliage of Pacific Water Parsley is toxic to
mammalian herbivores and humans. Considering the extreme toxicity of similar
members in the Carrot family, it is best to error on the side of caution and
avoid eating this plant. Deer have not been observed eating this plant in the
Pacific Northwest.
Photographic
Location: Along a small slow-moving stream at Meadowbrook Park in
Urbana, Illinois. Some of the plants were growing in shallow
water.
Comments: Distinguishing the
different members of the Carrot family with small white flowers is difficult.
Pacific Water Parsley resembles the cultivated form of Leaf Celery, which is
referred to as Apium graveolens secalinum. Leaf Celery (as well as other
forms of Cultivated Celery) also has compound umbels of small white flowers,
however they are lacking both bracts and bractlets. The different forms of
Cultivated Celery have not been observed to naturalize in the wild in Illinois.
An uncommon native species, Berula erecta (Low Water Parsnip), occurs in
the northern half of Illinois. Low Water Parsnip resembles Pacific Water
Parsley somewhat, but it has simple pinnate leaves only. The larger compound
leaves of Pacific Water Parsley are often double
pinnate.