Lobelia dortmanna
An isoetid aquatic plant that absorbs carbon dioxide through its roots.
Lobelia dortmanna, also called Dortmann's cardinalflower or water lobelia, is a perennial aquatic herb in the bellflower family. It spreads by stolons and forms basal leaf rosettes, sending up flower stalks that reach 0.7 to 2 meters tall. The flowers, borne in groups of one to ten on an erect raceme above the water, are white to pale pink or pale blue, with five lobes, each bloom 1 to 2 centimeters long. The fruit is a capsule 5 to 10 millimeters long and 3 to 5 millimeters wide, packed with tiny seeds.
Its leaves are nearly cylindrical, blunt-tipped, evergreen, and 2.5 to 7.5 centimeters long. They lack functional stomata. The plant is one of several unrelated species—called isoetids—that live in low-nutrient lakes and look superficially like quillworts. But its leaves are easy to tell apart from other isoetids: they have only two air canals (Isoetes has four, most others have several) and contain milky sap. Unusually, this species pulls carbon dioxide from the rooting zone rather than from the air.
The plant appears on the coat of arms of Ādaži Municipality in Latvia, adopted in 2022, and is endangered there, found in local lakes.
**Distribution** Lobelia dortmanna grows in cool temperate regions of northern Europe—from the British Isles and northwest France to northwest Russia—and across northern North America, on both coasts. In the east, it ranges from Newfoundland south to New Jersey and west to the Great Lakes; in the west, from British Columbia south to Oregon. Its northern limit reaches northern Norway, above the Arctic Circle.
**Ecology** It typically lives in shallow water on sandy, peaty, or rocky lakeshores, in pools, and in some wetlands, but rarely in rivers. Low water can leave it temporarily exposed, but it is sensitive to prolonged drying and is one of the first species lost when lake levels are artificially managed. The plant is a poor competitor, so it sticks to areas with sparse plant cover and low sedimentation, usually at depths less than 1 meter. It often grows alongside other isoetids like *Littorella uniflora*, *Isoetes lacustris*, *Isoetes echinospora*, and *Subularia aquatica*. Because it signals infertile, relatively pristine shoreline wetlands, it is at risk from eutrophication and serves as an indicator of clear water and the possible presence of other, less obvious isoetids.
Quick Facts
- Genus
- Lobelia
- Species
- dortmanna
Facts from the source article.
Lore & Background
Lobelia dortmanna is a stoloniferous herbaceous perennial aquatic plant with basal leaf-rosettes and flower stalks, growing to 0.7–2 m tall. Its flowers are 1–2 cm long with a five-lobed white to pale pink or pale blue corolla, produced in groups of one to ten on an erect raceme held above the water surface. The fruit is a capsule 5–10 mm long and 3–5 mm wide, containing numerous small seeds. The leaves are almost cylindrical, blunt, 2.5–7.5 cm long, evergreen, and have no functional stomata. They are easily distinguishable from those of other isoetids by having only two air-canals and by the presence of milky sap. The plant has the unusual ability of removing carbon dioxide from the rooting zone rather than from the atmosphere. It is featured on the coat of arms of Ādaži Municipality in Latvia, adopted in 2022, and is an endangered plant found in lakes within that municipality.
Reader's Guide
Lobelia dortmanna is native to cool temperate regions of northern Europe (from the British Isles and northwest France to northwest Russia) and northern North America (both coasts; Newfoundland south to New Jersey and west to the Great Lakes in the east, and British Columbia south to Oregon in the west). It reaches its northern limit in northern Norway, north of the Arctic circle. The plant typically occurs in shallow water on sandy, peaty or rocky lakeshores, in pools, and in some kinds of wetlands, rarely in rivers. Low water periods may leave it temporarily emersed, though it is sensitive to prolonged emersion and is one of the first species lost when water levels in lakes are artificially managed. It has relatively low competitive ability and tends to be restricted to areas with low plant cover and low sedimentation rates at depths of less than 1 metre. It often grows with other isoetids such as Littorella uniflora, Isoetes lacustris, Isoetes echinospora and Subularia aquatica. It is regarded as an indicator of infertile and relatively pristine shoreline wetlands, and can be put at risk by eutrophication. Lakes where it occurs are often referred to as Lobelian lakes, a specific habitat designated as type 3130: 'Oligotrophic to mesotrophic standing waters with vegetation of the Littorelletea uniflorae and/or of the Isoëto-Nanojuncetea'. In Europe, Lobelian lakes are relatively abundant in more mountainous areas.
Did You Know?
- Lobelia dortmanna has no functional stomata on its leaves.
- Its leaves have only two air-canals, unlike Isoetes which has four.
Frequently Asked Questions
What is Lobelia dortmanna?
Lobelia dortmanna, commonly known as Dortmann's cardinalflower or water lobelia, is a perennial aquatic herb in the bellflower family. It is a fully submerged plant that forms dense mats of small, cylindrical leaves in still or slow-moving freshwater habitats.
How does Lobelia dortmanna spread and grow?
This plant propagates vegetatively through stolons, creating a creeping network of basal leaf rosettes along the substrate. Its flowering stems rise vertically out of the water, reaching anywhere from 0.7 to 2 meters in height.
What do Lobelia dortmanna flowers look like?
The blooms are small, measuring just 1 to 2 centimeters in length, and come in shades of white, pale pink, or pale blue. Each flower has five distinct lobes, and they cluster in groups of one to ten along an upright raceme that extends above the waterline.
How does Lobelia dortmanna reproduce?
After flowering, the plant produces a small capsule fruit roughly 5 to 10 millimeters long and 3 to 5 millimeters wide. This capsule is packed with numerous tiny seeds that disperse to establish new colonies.
What makes Lobelia dortmanna unusual among aquatic plants?
It is classified as an isoetid, meaning it absorbs dissolved carbon dioxide directly through its roots rather than relying solely on leaf surfaces. This adaptation allows it to thrive in nutrient-poor, soft-water environments where many other submerged plants struggle.
More in Aquarium and Aquatic Plants, Part 2 1-24
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