White flowers recently seen in the greater Carderock area.
Virginia bluebells (Mertensia virginica; Boraginaceae) are of course normally blue, but every once in awhile you’ll see a stand of white ones. Look for them in floodplains and adjacent moist slopes.
Look for twinleaf (Jeffersonia diphylla; Berberidaceae) on rocky slopes along Billy Goat B; it will likely be done blooming by tomorrow.
Moss phlox (Phlox subulata; Polemoniaceae) should be blooming for at least another month. As you can see from the photo, it doesn’t need much soil. Look for in on large rock formations along the Potomac River. 
Lyre-leaved rockcress (Arabidopsis lyrata; Brassicaceae) is another rock-loving species. They’re so wispy they can be hard to see, but should be blooming for at least another month.
Bloodroot (Sanguinaria canadensis; Papaveraceae) is almost done blooming. You can find it in rich woodlands, usually in colonies.
Early saxifrage (Micranthes virginiensis; Saxifragaceae) grows in thin soils in rocky woodlands. It’s one of the earliest bloomers but lasts for a fairly long time.
Rue anemone (Thalictrum thalictroides; Ranunculaceae) is just starting to bloom. It’s common in the Maryland piedmont but for some reason there isn’t much of it in the Potomac gorge. Look for it in the very open wooded areas near the Marsden Tract. It should bloom for another month.
Dutchman’s breeches (Dicentra cucullaria) and the closely-related squirrel corn (D. canadensis; Papaveraceae) are both blooming in moist woodlands. In past years I’ve observed that the latter starts blooming a week or so after the former, so if you want to see both, go hunting soon. Neither lasts for long.
Elizabeth's Wildflower Blog 