Victorin's water-hemlock (Cicuta maculata) COSEWIC assessment and status report: chapter 6
General
Victorin’s water hemlock is a herbaceous perennial 0.5 to 2 m high. It flowers from June to September, and fruiting begins in August and continues until September (October according to Legault, 1986). Water hemlock seeds are surrounded by a spongy fruit coat that keeps the fruits buoyant until they are thoroughly saturated with water. This aids in the dissemination of fruits by water (Mulligan and Munro, 1981).
Reproduction
Victorin’s water-hemlock is a herbaceous perennial with a short rootstock. A bundle of 5 to 10 tubers grows from the base of the rootstock. Despite the large number of tubers that make up the rootstock, no signs of vegetative reproduction have been observed. Reproduction appears therefore to be by seed production.
Victorin’s water-hemlock requires vernalization (cold treatment) to induce flowering, which occurs between June and September (Legault, 1986). The flowers are considered to be generalist entomophilous, meaning that they are not specifically adapted to a particular insect (Bell, 1971). Pollen is spread by insects crawling over the inflorescences. The stylopodium has nectar-secreting glands and is brightly coloured (Heywood, 1971), likely attracting feeding insects. Mulligan and Munro (1981) observed the development of an umbel of Cicuta maculata var. maculata. The flowers on the outside of the umbel opened first. Their stylopodium did not exude nectar and the stamens did not dehisce immediately. The stigma consisted of two rudimentary knobs at that time. The five stamens unrolled one at a time and spread out from the flower. Individual anthers dehisced on the side away from the centre of the flower. The whitish-green stylopodium began to exude nectar as the first anther dehisced and the bilobed stigma elongated until all stamens matured. The percentage of fruiting varies from umbel to umbel and from plant to plant and depends partly on the activity of unspecialized pollinators. A succession of inflorescences are formed over the growing period, but those that are formed last produce the least fruit (Mulligan and Munro, 1981).
Survival
No data available is available on the factors affecting the species’ survival. The main cause of mortality in Victorin’s water-hemlock is currently the use of all-terrain vehicles in the mid- and upper littoral zones.
In a number of the localities visited in 1997 and 2002, the umbels and fruits of the plants were covered with hundreds of aphids. The impact of these invasions is unknown at this time, but maturation of the fruits has to be affected. This phenomenon was not observed in the sampling sites in 1995 or 1996. Victorin’s water hemlock may be a host to the fungal pathogens Puccinia cicutae and Uromyces lineolatus, which were discovered on spotted water hemlock by Ginns (1986).
Physiology
Victorin’s water-hemlock is a herbaceous perennial that forms rosettes the first year from seed. During the growing season, new rootstocks and storage roots form around the old rootstock. In the fall, the old rootstock, leaves and stem die and only the new rootstocks and storage organs overwinter; these produce new shoots the following year. The rootstocks form mainly underground. Despite the large number of tubers that make up the rootstock, no signs of vegetative reproduction have been observed. Reproduction therefore appears to be by seed production.
Victorin’s water-hemlock requires vernalization to induce flowering, which occurs between June and September (October according to Legault, 1986). Fruiting begins in August and continues until September (October according to Legault, 1986). Water-hemlock seeds are surrounded by a spongy fruit coat that keeps the fruits buoyant until they are thoroughly saturated with water. This aids in the dissemination of fruits by water (Mulligan and Munro, 1981).
Movements/dispersal
No detailed studies have been conducted on population dynamics in Victorin’s water-hemlock. Caldwell and Crow (1992) studied the dynamics of estuarine environments and found three factors that contribute significantly to plant community structure. The duration of flooding by tides is the most important factor, followed by the life forms present and physical disturbances caused by ice boulders. The plants that are the most successful in such fluctuating environments are annuals and highly rhizomatous perennials, such as Victorin’s water hemlock. A large number of rootstocks allow these plants to maintain an equilibrium between sedimentation and constant erosion and to store nutrient reserves in order to emerge and grow quickly. Abundant seed production in late summer or early fall are the principal means of reproduction in water hemlocks (Lynn et al., 1988). The seeds generally fall near the parents and are protected in the marsh surface microrelief, where they can be dispersed by various means (Kingsbury, 1964; Muenscher, 1975; Lynn et al., 1988): anemochory (wind), hydrochory (water) and endozoochory (within animal bodies). In addition, ice boulders stir up sediments and even parts of the vegetation cover, which can be carried over large distances and redeposited along the River, thus contributing to their dispersal.
Behaviour/adaptability
Germination tests by Mulligan (1980) using seeds collected at Cap-Rouge and Saint-Augustin-de-Desmaures revealed that they did not germinate if they were over two years old. Younger seeds germinated only after a special treatment that consisted in soaking them overnight and removing the seed coat. They were then immersed in water on petri dishes and subjected to alternating temperatures (2°C to 21°C) every 12 hours for two weeks. The seeds were then exposed to a constant temperature of 21°C and germination began within two weeks.
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