Eryngium mathiasiae is a species of flowering plant in the carrot family known by the common name Mathias' eryngo, or Mathias' button celery. It is endemic to the Modoc Plateau of northeastern California, where it grows in the vernal pools of the local river drainages, and other wet areas such as ditches. This is an erect perennial herb 30 to 40 centimeters tall. There is a basal rosette of long lance-shaped leaves, the blades up to 17 centimeters long and lined with sharp-pointed serrations or lobes, borne on petioles several centimeters in length. The inflorescence is an array of flower heads, each surrounded by sharp, spined bracts. The greenish flower heads bloom in small, white petals.