Viola striata illustration
Britton, N.L., and A. Brown
<a rel="nofollow" class="external text" href="https://plants.usda.gov/java/largeImage?imageID=vist3_001_avd.tif">USDA-NRCS PLANTS Database / Britton, N.L., and A. Brown. 1913. <i>An illustrated flora of the northern United States, Canada and the British Possessions.</i> 3 vols. Charles Scribner's Sons, New York. Vol. 2: 560.</a>