Plants of the genus Bacopa have been popular aquarium plants for years. Most species within this genus are robust, easy to keep and persistend growers.
Whilst species such as B. caroliniana and B.monnieri are a common choice with aquarists, B. lanigera is kept only very rarely in Europe. B. crenata, a wonderful species, is not available at shops and is hence also a rare plant. B. madagascariensis is hardly ever on sale anywhere. B. spec. 'Purple' is so new that I have the privilege to introduce it here for the first time.
Woolly Bacopa (Bacopa lanigera)
First, I'd like to do away with a prejudice. It is often claimed that B.lanigera is hard to keep. Whilst it is true that its submersed growth is slow and roots are only produced sparsely, in my experience this plant has turned out to be a good grower and is generaly trouble-free. It does not have particular demands as to water quality (albeit I use almost pure rain water due to the hardness of the tap water in Münster), nor does it seem to need any special fertilizer treatment. The only thing it needs is strong light. The Wolly Bacopa tends to lose its lower leaves, which is probably even more pronounced under low light. Due to this tendency, it is best kept as a midground filler with frequent re-planting according to the classic Dutch method for planted tanks. At the same time, you can cover the lower portions of the stem with medium high foreground plants. (H. corymbosa 'Compact' is a good choice). Due to this frequent care, B. lanigera will never reach great heights, making it an ideal midground plant. One of my favourite features of this plant is its bright green colour which will never convert to red, even under very bright lights.
Dentated Water-Hyssop (Bacopa crenata)
Another candidate with brigth green leaves, also witout the tendency to develop any red pigment, even under high light. Its green is of a particularly pale shade, which creates the impression of great freshness - a feature much desired in Nature Aquariums. Root development is strong and this plant will grow best on a good quality, iron-rich aquarium substrate. Interestingly, this plant will show twisted or distorted leaves if something is not right. For healthy plants, the submerged form is indiscriminable from the emersed form. Use strong lights to keep this plant happy. Recommended position is in mid- to background. Do not re-plant too often. (Not that you will have to as its growth is not fast). Propagate through cuttings but do not wait too long as the remaining stems should have at least 2 to 4 leaves left.
My personal favourite. Despite its similarity to B. monnieri, some of it's features are very unique and characteristic. Its habit is always upright, even under strong light, whilst its growth rate is slightly slower - a real boon for maintenance. I really value this plant for its leaves, though: They are never twisted or rolled in at the sides, like B. monnieri's leaves often are. The slightly stiff habit is created by its relatively thick stem compared to the rather small leaves. It is this charcteristic appearance which makes B. madagascariensis such a wonderful accent plant.
Ruby Bacopa (Bacopa spec.'Purple')
Its similarity with B. caroliniana suggests close relation of the two but this is yet to be confirmed. The Ruby Bacopa is slightly smaller than B. caroliniana. Its striking ruby red colouration is present under normal light and does not require extreme illumination to develop. Describing the hues of green and red that this plant displays requires some poetic talent I cannot muster :).
Its leaves display a variation of hues from bright green down to deep purple red. This spectacular play of colour make this plant a wonderful red accent but interestingly, it lends itself also to be used as a companion for other red plants, as the above picture demonstrates (Ludwigia ovalis in the background here).
Southern Bacopa (Bacopa australis)
This plant, which looks rather atypical for a Bacopa, is still relatively new but has already taken a firm foothold in the world of aquascaping. Its thin stems, bushy growth and round, light green leaves remind of a larger form of Baby's Tears (Micranthemum umbrosum). In actual fact, this Bacopa is much easier to look after, tolerates a larger scope of water conditions and -temperatures and thrives under low to high light. If you want compact, bushy growth, you should provide sufficient light, though. B. australis takes some time to settle in but once it has taken root, it needs to be trimmed at least once a week. As soon as a dense clump has formed, it will be difficult to keep the shape by weekly trimming and a more radical cut-back may become necessary. Allow for some time for the remaining plants to recover. This may take a while. If you want to avoid your plants looking a bit rough for a while, you can always re-plant the cuttings after removing the entire clump.
One of the most outstanding properties of this Bacopa is its truly dense, you could even say, opaque, growth habit. No other species is capable of forming continuous clumps from fore- to background with a similar tolerance to trimming. Maybe this is the best plant for Dutch Style "Streets" yet.