Mesa Tansyaster

Machaeranthera tagetina

About the Plant

Mesa tansyaster is a summer-blooming annual that spreads readily but is always welcome. Though small in stature, it produces abundant purple and yellow daisies. Mesa tansyaster is native to Arizona, southern New Mexico, and Mexico. It resembles spiny goldenweed, which was once placed in the genus Machaeranthera.

Mesa tansyaster begins to grow in spring and may bloom a bit if rains are ample. However, most flowers appear in August and September. Don't be surprised if the lower leaves start to brown as flowering begins. Expect mesa tansyaster to appear most abundantly near irrigated plants. It is an annual and can happily coexist with other plants during its short lifespan. When the plants die in late fall, clean up by cutting or breaking the plant at its base. Make sure to shake well to scatter any remaining seeds for a show next summer.

Notes: Machaeranthera tanacetifolia (tansyleaf tansyaster, Tahoka daisy) is a closely related species also found in Arizona and more broadly throughout the desert Southwest and the western Great Plains. It has more petals and disc flowers and a larger flower head than mesa tansyaster (2 inches compared 1 inch). The two species may hybridize where their range overlaps, so an absolute ID may be difficult.

Wildlife value: attracts insects, especially small butterflies and bees

More Information

Weekly Plant on mesa tansyaster

Map of distribution in US

Technical botanical description from SEINet

ID Characteristics

This plant is in the Asteraceae - the aster family.
Mesa tansyaster is a small plant, usually growing about 8 inches tall and wide with a rounded habit. If it finds a spot near irrigation, it can become larger, 2 feet high and 3 feet wide. It has many branches with a single flower head at the end of each.
The leaves are alternate and lobed, often with a bristle tip on the ends of the lobe. They are sessile (there is no petiole) and are held somewhat upright so they are not very noticeable (photo above taken looking down on the plant). Each leaf is 1/2-1 inch long and 1/4-1/2 inch wide, becoming smaller near the top of the plant. As the plant begins to flower, the lower leaves often turn brown. The leaves are covered with glands (see below).
The flower heads are terminal and solitary, each about 1 inch across. The petals are typically purple, usually fairly dark but occasionally pale, almost white. There are usually no more than 16 petals. The disc flowers are bright yellow (typically fewer than 40 flowers).
The underside of the flower head is made of several rows of phyllaries whose ends bend outward. Often the lower half of the inner phyllaries is white.
The stems, leaves, and phyllaries are covered with glands shaped like lollipops. Please click on the photos of the leaves and flowers to enlarge.
Each flower head matures into a small, rounded seed head. The individual seeds are dark and may look as if they are ribbed with hairs. Each seed has a tuft of bristles on one end.