Is this Lilaeopsis brasiliensis?
Should I trim it to promote growth? I want it to spread thick along the front of my tank
I think this is more likely
Sagittaria subulata. The leaves seem wider, thicker and longer than
Lilaeopsis brasiliensis. A third very similar plant is
Helanthium tenellum (formerly
Echinodorus tenellus so it may still be seen under this name). Conditions in the aquarium can affect the appearance of these three plants quite a bit, often making them difficult to distinguish at least from still photos. I have all three, and for me
L. brasiliensis is distinctively narrow leaf and much shorter than what would appear in your photos.
Of course, if these are newly acquired, they may be emersed cultivated plants. All three species are marsh or bog plants, growing either emersed or submersed or both depending upon their habitat. Emersed leaves will obviously be much stronger than submersed, as they have different structures. Nurseries prefer emersed cultivation where it is possible because it is much faster and thus less expensive.
H. tenellum is quite rapid at spreading, once it establishes (up to a few months, depending).
S. subulata I find very slow.
L. brasiliensis is so slow it is almost static, but it does go through spurts of runners every so often. This latter is known to be slow spreading, even in high tech conditions.
Byron.