IME with both CO2 injection, lower light non CO2, lower light Excel, and even the same clippings taken to the LFS and grown there, the same species of Staurogyne, which I recieved from Tropica is very variable in growth and resembles three different "so called species" identified by others.
IME very slow growing, when shaded will grow upwards, otherwise will creep along the substrate. With CO2 injection, if CO2 injection is off or varies to much the leaves will curl and stunt, a classic CO2 deficient symptom. This condition will persist until adequate CO2 levels are constant and can take quite awhile to correct. In my non CO2 its much the same as CO2 injection except a much smaller plant, and with Excel is pretty much the same. The cuttings grown at the LFS took nearly 3 months for it to take off, but once established grow completely different then any of my setups. The most notable difference is size and shape of the leaves. Leaf size is easily half and instead of pointed tips, the tips are more rounded.
The most notable thing with this plant IME has been if its unhappy it takes quite awhile for it to bounce back.
Also IME it does not require a great deal of light to survive. In my 150 its has become completely overgrown by Blyxa and HM and slowly but surely creeps along and finds its way out of the thicket. The stem will elongate under this condition until it reaches more lighting then will become more compact.
I have to agree with Tropica's
assertion to cut vertical growth to encorage horizontal spreading.