Water soldier, Stratiotes aloides

Water soldier, or water pineapple, is a weird relict species of aquatic plant in Finland and in Sweden. The English name is easy to understand from the appearance of the species. It looks like a pineapple, and its leaves are sharply serrated like soldiers’ swords.

Stratiotes aloides looks like a pineapple leaves under water.
Photo by Manuel Deinhardt, Metsähallitus.

It was left here in the lakes during the warmer period after the last Ice age 10 000 years ago and has struggled in shallow lakes and ponds in central Finland, south Sweden and Lapland ever since. In the SEAmBOTH area it is found in the river estuary of Kemijoki River in Finland. In Sweden it exists mainly in the south, but also all the way north, but mainly in fresh water ponds. The plant has been classified NT (nearly threatened) in Sweden since 2000, due to the same overall decline as in Finland. In Sweden it has gathered the most observations in rock pools on the west coast, but it is found in both lakes and estuaries in the rest of Sweden. In the SEAmBOTH area in Finland it has mostly been found in estuaries but also on shore meadows in the archipelago. Here in the north, the plant grows much smaller than in other parts of its vast distribution area of Europe and northwestern Asia.

Stratiotes aloides under water.
Photo by Essi Keskinen, Metsähallitus.

Water soldier is a strange species in many ways. It grows as unattached and floats near the bottom or is slightly attached to the bottom until it starts to flower, when it suddenly rises to the surface where its leaves and flowers stick out of the water. The species is dioecious, meaning that there are male and female flowers which are both needed for pollination. In Finland, only male flowers have been found, so the plant reproduces from overwintering rosettes which develop at short runners at the end of the summer. The flowers smell like decomposing flesh in order to attract pollinators, which will never find the female flowers to pollinate in Finland.

Another strange thing is the family tree of this species. The plant belongs to the Hydrocharitaeae family where its relatives are an invasive species pondweed Elodea canadensis and naiad Najas spp. Water soldier is found to be an invasive alien species in Ontario, Canada, where it has escaped to natural waters from ponds and aquariums. It is now prohibited in Canada under the Invasive Species Act.

Water soldier has sharply serrated leaves. Growing with Elodea canadensis.
Photo by Essi Keskinen, Metsähallitus.

One more weird fact about this interesting species – it provides an egg laying place for the rarest Finnish dragonfly (Aeshna viridis) (VU). This choosy dragonfly is not found anywhere else in Finland except in waters with the water soldier.

Wikipedia tells us that “The herb has had a high reputation for treating wounds, especially when these are made by an iron implement. It is applied externally. The plant is also said to be of use in the treatment of St. Anthony’s fire and also of bruised kidneys.”

Whether the healing powers of water soldier are true or heresy, this is an interesting water plant that can be found in small pockets of fresh or almost fresh water here and there in Finland and Sweden.

If you want to know more about the species of the SEAmBOTH area, see species guides on the Results page!

Written by, Essi Keskinen


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