Audouinella

Audouinella, also known as black algae,[1] is a widespread genus of red algae, found in marine and freshwater environments. It grows as small tufts of red, brown, or black hairlike filaments on any solid surface - most dramatically in freshwater on the edges of slow-growing leaves. Often tolerant of high levels of pollution, acidity, Audouinella thrives on dissolved phosphate and nitrates. It reproduces via spores, most commonly asexually, while sexual reproduction is known in rare examples [2].

Audouinella
Scientific classification
(unranked):	Archaeplastida
Division:	Rhodophyta
Class:	Florideophyceae
Order:	Acrochaetiales
Family:	Acrochaetiaceae
Genus:	Audouinella Bory de Saint-Vincent

The form known as "black brush algae" (or "black beard algae", BBA for short) is a particular nuisance in aquaria, as few fish, even those widely promoted as algivores, will eat it.[3] In natural ecosystems, this genus that infests aquariums is found in unpolluted lotic systems.

It has been tested for germination and new growth using NO₃ and PO₄ fertilizers and such results came out negative for a decade's worth of observations. It has been shown to be inducible by limiting and varying the CO₂ concentration in planted aquariums. While other possible inducement mechanisms may exists, this is the most consistent and has been shown in many test by aquarists.

Its thalli are composed of uniaxial filaments, the ends of which often contain elongate hairs.[2]

Jean Baptiste Bory de Saint-Vincent named the species to honour Jean Victoire Audouin, his co-editor in the Dictionnaire Classique d'Histoire Naturelle.