Ask Mr. Smarty Plants

This is a really tough question.  Many plant experts venture no farther than confirming that a cross-section of the stem is triangular (all sedges) rather than round (grasses).  The problem is that there are so many species of sedges that are quite similar.  The main differences often are in the shape and appearance of the seeds and/or the arrangement of the seed clusters on the mature reproductive stems.  But even these properties are very similar in certain species, and sometimes the properties show significant variations depending on where the sedge is growing.

I am assuming that you are interested in the native sedges growing in the Houston area.  I would first go to the Lady Bird Johnson Wildflower Center Plant Database and under the Combination Search enter Texas for the State, grass/grass like for the Habit , perennial for the Duration and moist for the Soil moisture.  Click on Submit and you will get a list of several sedge (Carex) species.  Here, I have done it for you! Unfortunately, there are no images for some of these to help you, but the description may be useful.  For more information after clicking on a particular species, look at the bottom of its Plant Database page for Additional Resources and click on the USDA site and/or on Google. You can find photos of most of the species there.  The "flowers" and seeds of the different species are fairly characteristic.  But bear in mind that the appearance of the fruiting structures changes with time, sometimes markedly, as the pollen is produced and then as the seeds progress to maturity.

In this way you can narrow your search to those species native to your area. For a listing of sedges throughout the entire U.S., including Texas, check out a Department of Agriculture web site devoted to these plants by scrolling down the list to the Carex species.

This hit-or-miss approach is about the best I can suggest.  For me, it has worked sometimes but not always.

Sedges are a good alternative ground cover in shady areas where grass does not grow well.  But you will want to avoid the very invasive non-native sedge, Cyperus rotundus, commonly called nutsedge, coco grass, or other names I am too polite to mention.  This sedge is almost universally present in lawns, where it invades adjacent flower beds and is nearly impossible to eliminate.