Synonyms for Snow-in-summer (same or very similar meaning)
WordNet sense 1 (annual spurge of western United States having showy white-bracted flower clusters and very poisonous milk):
snow-on-the-mountain, ghost weedWordNet sense 2 (chickweed with hairy silver-grey leaves and rather large white flowers):
love-in-a-mistFrom the ODE community, based on WordNetadd/edit