Courtesy of Bill and Dolphia Bransford, Lady Bird Johnson Wildflower Center
Bracted Twistflower (Streptanthus bracteatus)
Bracted twistflower is an annual herbaceous plant in the mustard family (Brassicaceae) that occurs only along the southeastern edge of the Edwards Plateau of Texas. It is currently listed as threatened by the U.S. Fish and Wildlife Service (USFWS) because many of its populations have been lost to development, browsing by white-tailed deer and feral hogs, juniper encroachment, and other causes.
Seeds germinate in the fall to produce a leafy circular arrangement of leaves similar to a dandelion or radish over winter. During the spring, they send up a stalk 1 to 4 feet tall which bears four pedaled lavender/purple flowers.
Bracted twistflower can be distinguished from most other members of this genus because the leaves on the flower stalk lack stems, and all flower stems have a small, modified leaf, called a bract, at their bases.
Current Range Map
Know populations are primarily in Uvalde, Medina, Bexar, and Travis counties, with suitable habitat and past occurrences also taking place in Bell, Comanche, and Williamson counties.
The flower is commonly associated with rocky hillsides and slopes of the Edwards Plateau area which contain Live Oak, Juniper (Cedar) trees, and other shrubs. It is likely these habitats are preferred due to their ability to provide protection from grazing. The species is most prevalent in areas where different geological formations meet, providing higher seepage rates or limiting nutrients being more available in that area. It appears to be a species that benefits from fire, limiting competition from other plants and being shaded out by Junipers (Cedar).
Seeds germinate in the fall, producing a leafy mass that stores nutrients through winter. In the spring, it forms flowering stalks and relies on native bee populations for pollination. It then forms long seed pods and disperses the seeds locally. The seeds can survive in the soil for several years, waiting for appropriate conditions, such as a wet fall to trigger germination.
Ongoing Research/Conservation Efforts
Many of the critical habitat areas are in city and state-owned parks and preserves. The city of San Antonio is protecting some populations by fencing out herbivores.
Read more about the other threatened species of interest here.