Allium elmendorfii, or Elmendorf's onion, is a species of wild onion endemic to Texas. It is known only from Bexar, Frio, Wilson, and Atascosa Counties. It is generally found on sandy soils, specifically "well-drained sands, Eocene, Pleistocene and Holocene sands, and has only a 400 x 160 km range." Its habitat is "Forest/Woodland, Savanna, Woodland - Hardwood" and specifically "{g}rassland openings in post oak (Quercus stellata) woodlands on deep, well-drained sands derived from Queen City and similar Eocene formations."

Allium elmendorfii is a perennial bulb-forming herb with clusters of small bulbils around the roots, but without the dry papery outer layers that the domesticated onions have. It has an umbel of 10–30 erect to spreading flowers, each with 6 white to pinkish tepals about 5 cm (2 inches) long, flowering from March to April or May.

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