Rotala Magenta, Narrow-leaf Variety

[lljdma06]

Common Name(s) - Giant red rotala, rotala magenta

Scientific name - Rotala macrandra (discussed is the v. "narrow leaf")

Family: Lythraceae

Geographic origin - India

Type (stem, bulb, rhizome, floating, etc.) - Stem

Max. size (height, width) - Up to 50cm, leaf length 1-2cm long, 3-5mm long, very similar to R. rotundifolia, though I have not experienced it growing to rotundifolia's height.

Lighting required - Was thought of as high to very high, but see the second post below

Temperature - 25-30 degree C

Water chemistry requirements (pH, hardness) - Previously though to thrive in softer water conditions and that low nitrates brought out more intense red color. Please see thread below for new evidence.

Growth rates - medium. One of the slower growing stem plants.

Demands - Thought to need bright light to thrive, clean water, high nutrients. Most would recommend bright light, CO2 injection, and EI fertilization to maintain optimum growth. If these demands are met, it is a low-maintenance plant since it doesn't require the extensive pruning required by the faster-growing stem plants. Supercoley, however, has recently grown R. macrandra with much lower lighting.

Additional info - This is a more delicate species of Rotala. The intense red color provides a lovely contrast, especially with green myriophylum and egeria najas, as I have in my tank. It grows at a much slower rate than your average stem plant and its stems tend to be very delicate. R. macrandra is propogated from cuttings. It is a great mid-ground plant that creates a very nice focal point. The bottom leaves are prone to decay from lack of light, so it is best to plant the stems individually or in very small groups, 2-3 stems maximum. It also tends to get algae on its leaves, so the tank must be very clean. Plants from mail order and online sources will arrive a bright, bright red, but unless your home aquarium lighting is extremely bright, the color will fade over time, though the color will remain quite reddish. I grow mine with 3.73 WPG, and though it did survive in my 10g at 2.8 while my 15g was undergoing a blackout, I generally would not recommend this plant for a low-light setup, though others have done so. One of my sources implied that low Nitrate levels bring out the red color, so I put that down, and my nitrate levels tend to be on the low end (despite dosing), so I am wondering if this is in fact the case with this species? My plants tend to stay pretty red, especially my newer specimens, but I am not sure if this is due to my nitrate levels or the fact that I also dose Iron. Here are a few pictures of this plant.

 

[SuperColey1]

Not to undo what Llj has said in the original post here because it is 3 years old and indeed gives the commonly understood thinking on the plant but I have some other ideas to share on this one.

Basically I don't believe in all the 'This plant requires highlight or it will die' theories. they are well understood and 99.9% of the planted community would disagree which is fine as there is currently no real proof to the contrary. I won't go into my theories of lighting principles here as that is for another place but will share some basic findings on the plant itself.

Where Llj used 3.73WPG I experimented with this plant with 0.9WPG of T5HO This was over a 33USG tall tank (about 15" from substrate to water level) on a lean PMDD+PO4 dosing method and with high (25-35ppm) pressurised CO2

One of the actual 'predictions' on the original 'test' thread was (unedited):
LOL...Tthat plants will melt like plastic hitting my stovetop

Far from the plant dying off it actually grew very healthily. A little leggy perhaps but the same sort of colour as Llj's pictures. Peachy yellow. If anything maybe it was a little redder.

My thoughts on this plant are that yes it is very delicate. when you buy it the leaves are inevitably damaged. You can expect these leaves to gradually disintegrate. New growth should survive nicely. I would suggest buying it and then after a few weeks when the new growth is long enough carefully removing the plant, cutting off the old growth and then carefully replanting the top so that you have a nice undamaged all new growth plant.

Some pictures of the actual plants from Day1, then after 2 weeks and finally after 4 weeks.

So my conclusions are that this plant does not need high light to survive. It does require good light in that is should not be shaded so yes you could call direct light a need. Far from melting the plant grew healthily, just taller and with more space between nodes. Under high light you should expect more compact growth but not the redder colouration as Llj's pictures show.

The colouration is the same as LLj shows above under 3WPG+ as it is under 0.9WPG so that shows that the colouration is not light driven. It must be something else that gives the intense red appearance we often see in 'show' tanks. This tank did have high CO2 added so we can rule CO2 out as a cause of the red too. I doubt it is low nitrate levels because at the time this tank was lean dosed with a huge plant mass within it so nitrates would've been low. Llj's was also low on nitrates.

I don't think it prefers softer water either. The water I use from the tap is stated as being hard to very hard.

Why does this plant go so red? Who knows. I doubt it is actually a nutrient that causes it unless it is a forced defficiency that give the plant a false colour. It could even be temperature in that I have seen emergent plants turn brighter colours when they get hotter. This is something for others to talk about and discuss. Even the experts in planting do not know the exact truth on this subject yet and there are several theories suggesting reasons. Try all the theories and see if any work.

AC