Description from Possibility Place: Heart-Leaved Alexanders have bright yellow umbels of flowers that are 2-3 inches across. They bloom in May and last about a month. Unlike the more common Zizia aurea, this plant has heart-shaped, smooth basal leaves and can tolerate drier conditions. Clumps can become quite large, and divisions in the spring can prevent overcrowding.
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Information from Prairie Moon Nursery: Zizia aptera is a member of the Carrot (Apiaceae) family with yellow umbel flowers. Our website also features the following species with similar blossoms: Taenidia integerrima (Yellow Pimpernel), Polytaenia nuttallii (Prairie Parsley) and Thaspium trifoliatum (Meadow Parsnip). Of course, Zizia aurea (Golden Alexanders) is most similar and could be difficult to distinguish from Zizia aurea were it not for the heart-shaped leaves at the base of the plant. All of these important perennial native plants should not be confused with the similar-looking Pastinaca sativa (Wild Parsnip), a highly invasive Eurasian biennial commonly found on roadsides and other disturbed sites. Wild Parsnip is taller than the aforementioned natives, blooms later, and can cause painful skin burns.