frostweed or frostwort, North American woodland flowers (Helianthemum canadense and sometimes other related species) of the family Cistaceae (rockrose family). In cold weather, crystals of ice shoot from the cracked bark at the base of the stem. The names frostweed and frostflower are also used for several other unrelated plants that have white flowers or bloom late (e.g., the asters). Frostweeds are classified in the division Magnoliophyta, class Magnoliopsida, order Violales, family Cistaceae.