Aquatic plants, at least underwater ones that live submerged, always under water, are a subject for few specialists. Anyone who is not one of these specialists is seeing nothing more than something green under water. Underwater plants seem all to be the same, something chaotic, at best this underwater jungle is understood as oxygenation plants.
But it is worth trying to see a little bit more. For example, find Groenlandia densa or Opposite-leaved Pondweed. A vivid green plant, specialized in carbonated and oligotrophic waters (that is, from limestone geology and extraordinarily clean, almost like drinking water). Whoever once saw this plant next to a spring – because it always grows very close to springs – will be delighted about what nature knows how to create only with green tones. In the game of running water, between shade and sunlight, the leaves look like green pennies.
The Opposite-leaved Pondweed is a rare and threatened plant, described as “vulnerable” in the Red List of Flora of Portugal. On the one hand, it is naturally rare, because springs in calcareous waters are rare due to the country’s geology and, where they do exist, they are often already so contaminated with nutrients from agriculture, so the Opposite-leaved Pondweed is no longer there.
In biological pools we can use Groenlandia densa only in situations of heavily carbonated water, as they exist in the area of Leiria or Algarve. Also in these bathing biotypes, the species prefers places with moving water, where it develops its extraordinary beauty like an underwater penne shining in many shades of green.