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Drosera

English
Round-leaved sundew (Drosera rotundifolia)
Photo: Jardin botanique de Montréal (Normand Fleury)  

The genus Drosera comprises over 90 species in a great variety of shapes and sizes, from round to threadlike, simple or divided, in a rosette on the ground or along an upright stem, with simple or compound flowers, etc. One thing they all have in common is the glandular hairs that they use to capture and digest their prey. The leaf surface is covered with these hairs, sometimes referred to as “tentacles,” each one topped with a bright red oval gland. At the top of the gland is a droplet of viscous liquid that sparkles like morning dew – hence its name of sundew in English, rossolis in French and Drosera in Latin.

The trap

Although there is actually no proof of their effectiveness, it seems logical to assume that the red colour of the glands and the sparkling droplets resembling nectar must attract insects. The glandular hairs are especially numerous at the centre of the blade. They have three functions: they secrete mucilage that ensnares and holds the victim, produce the enzymes needed to digest it, and absorb the nutrients released when it decomposes. Any insect that lands on the droplet becomes stuck in the substance; as it struggles to free itself it activates the neighbouring hairs, which ensnare it even more securely. Digestion is only really efficient at the centre of the leaf, because of the small number of glands on the edges.

Of course, not every insect is obliging enough to land in the middle. The problem is solved by the fact that the glandular hairs get progressively longer toward the edges. When a victim is caught near one of the edges, the long hairs bend over, gradually moving the insect toward the centre. In many species – Drosera rotundifolia, for example – the very edge of the leaf can fold up around the victim. This brings a larger number of glands into contact with the prey, for quick and complete digestion, and reduces the likelihood of having rain wash away the nutrients. Once digestion is complete, the tips of the glandular hairs absorb the nutrients and then resume their initial positions, waiting for the next victim.

Species

Drosera rotundifolia Linnaeus

Common name
Round-leaved sundew, common sundew

French name
Droséra à feuilles rondes, rossolis à feuilles rondes

Description
Orbicular leaves (4 cm stalk and 1 cm blade) in a rosette. Flower stalk (10-15 cm) bearing a cluster of white flowers.

Habitat
Peat bogs, small marshy lakes, cedar stands, sandy beaches and alpine meadows.

Distribution in Quebec.
Widespread. It is by far the most common of the four known species in Quebec. It is easy to spot and invariably occurs in most peat bogs in Quebec and in moist sandy ditches.

Global distribution
Circumboreal species in the Northern Hemisphere

Drosera anglica Hudson

Common name
English sundew, great sundew

French name
Droséra d'Angleterre

Description
Linear-spatulate leaves, 6 to 8 times as long as they are wide, with bright red glands. Rosette of white flowers on a laterally borne stalk.

Habitat
Peat bogs, swamps or marshy ponds.

Distribution in Quebec
Eastern Quebec

Global distribution
Europe, North America and Japan

Drosera intermedia Hayne

Common name
Spatulate-leaved sundew, spoonleaf sundew

French name
Droséra intermédiaire

Description
Often confused with D. anglica, this species is distinctive because of its leaves, 2 to 3 times as long as they are wide, with dark purple glands, and the flower stalk emerging from the centre of the rosette. White flowers.

Habitat
Peat bogs

Distribution in Quebec
Widespread, but relatively uncommon

Global distribution
Locally common in Europe and eastern North America. Also found in Guyana.

Drosera linearis Goldie

Common name
Slender-leaved sundew

French name
Droséra à feuilles linéaires

Description
Very narrow leaves, 10 to 15 times as long as they are wide, rarely exceeding 2.5 cm in length. Cluster of white flowers on a stalk just slightly longer than the leaves.

Habitat
Peat bogs and calcareous fens. Unlike other Drosera, it prefers rather alkaline soil.

Distribution in Quebec
Included in the list of rare plants in Quebec (Bouchard et al., 1981 and 1983). Abitibi, Lac Mistassini, Laurentians north of Quebec City, Gaspé Peninsula and Anticosti Island

Global distribution
North America. Appears sporadically in a band from the Great Lakes to Labrador.

References:

  • Bouchard, A., D. Barabé, M. Dumais and S. Hay. "Liste préliminaire des plantes vasculaires rares du Québec", Bulletin de la SAJIB, vol. 6, no. 2, 1981, p. 44-48.
  • Bouchard, A., D. Barabé, M. Dumais and S. Hay. Les plantes vasculaires rares du Québec, Syllogeus, no 48, 1983, 79 p.

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