Myriophyllum rubricaule

This milfoil has been on the market as a garden pond plant for decades, but its species affiliation was unclear for a long time. This plant is only known from cultivation and was sometimes mistaken for the similar parrot feather (Myriophyllum aquaticum). In Europe it was mostly sold under the name "Myriophyllum brasiliensis" (M. brasiliense is a synonym of M. aquaticum). In English-speaking countries, the plant is also known as Myriophyllum aquaticum 'Red Stem' and "Red Stemmed Parrot's Feather". Although it is regularly sold as a pond plant, it is little known as an aquarium plant.

Due to its similarity to Myriophyllum aquaticum, which also forms blue-green, highly water-repellent leaves in the emersed form, the plant was named Myriophyllum cf. aquaticum 'Red Stem' in this database until 05/08/2024. In 2022 it was described by Johan L.C.H. van Valkenburg & al. as a new species under the name Myriophyllum rubricaule. The specific epithet means "red-stemmed". Molecular data indicate that although this milfoil is closely related to M. aquaticum, it can be distinguished as a separate species.

The emersed leaves of M. rubricaule are smaller than those of the "normal form" of M. aquaticum and have fewer pinnae. However, the emersed form of the variety Myriophyllum aquaticum var. santacatarinense is similar in size to M. rubricaule (H. Muth, own observation, ca. 2010). However, it has rather green emersed stems, whereas the stem of M. rubricaule is clearly brown-red both emersed and submerged.

The differences to the normal M. aquaticum are even clearer in the underwater form. In this case, the red-stemmed parrot feather is more similar to Myriophyllum pinnatum, but is not as densely covered with leaves as the latter because the internodes are significantly longer. The submersed leaves are often reddish in colour and have fewer, more spreading leaflets than normal M. aquaticum. The stem also turns a dark red colour in moderate light. In contrast, the submersed stems of the normal form of M. aquaticum are usually green in colour and the leaves are often orange-brown.

Natural occurrences of Myriophyllum rubricaule are apparently unknown. However, due to its relationship with M. aquaticum, which is native to South America, it is likely that the plant also originates from South America.

Myriophyllum rubricaule is a relatively easy aquarium plant to cultivate, but looks best with high light intensity, a complete supply of macro and micronutrients via the water column and the addition of CO2. The internodes are quite long in low light. Under favourable conditions, this milfoil grows very quickly and often needs to be pruned.

As a pond plant, the red-stemmed parrot's feather is apparently not reliably hardy in Germany. It does well as an emersed or semi-emersed plant in containers. Stems growing over the edge of the container hang down like a hanging basket plant. The dark red stem forms a beautiful contrast to the light blue-green emersed leaves.