Delicate Resilience: Bracted Twistflower

By Michaela Stenerson and Madeline Padgett

The Bracted twistflower, Streptanthus bracteatus, is a species of annual flowering plant in the mustard family Brassicaceae that is native and endemic to only five counties in Central Texas. The plant was listed as Threatened by the U.S. Fish and Wildlife Service in 2023. 

When Bracted twistflower is young, it grows in rosettes and can look similar to any member of the Brassicaceae family including cabbage, broccoli, or arugula. However, as it bolts into a flowering plant, it begins to distinguish itself. The plant grows a long stem, at times reaching up to four feet tall, with alternating leaves whose bases are wrapped directly around the stem. These bracted leaves are what give it part of its name. As it flowers, the plant opens up four lavender-pink petals and offers nectar and pollen for bees. After it bolts, the plant produces fruits that resemble long, thin, string beans called “siliques” in which it stores tiny seeds that are eventually dropped in the soil surrounding the plant in hopes that its lineage will continue. 

Conservation Concerns

Despite having such a limited range and small populations, the Bracted twistflower was only listed as Threatened in 2023, shockingly recent considering that the species lost one-third of its potential population in the last 30 years (U.S. Fish & Wildlife Service). The species is quite picky about where it survives and thrives, dangerous in our ever-changing, ever-developing world. 

Twistflowers prefer forests of juniper and oak trees, shady and brushy to protect from herbivory, but not too shady as to block their access to much-needed sunlight. Climate-wise, they prefer hot summers and milder winters, typical of the Austin and San Antonio areas where these flowers are found. Their preferences for precipitation remain a mystery, as rainfall and twistflower population fluctuate wildly from year to year. This species also seems to be a fire-following one. Karrikins, compounds produced by burned plant material, stimulate the germination of dormant seeds in certain species, including the Bracted twistflower (U.S. Fish & Wildlife Service).

Unfortunately, these preferences mean that Bracted twistflowers face a great many threats to their ability to survive. Austin and San Antonio have both experienced immense growth, leading to rapid development and a decline in viable habitat for the twistflower. The area around Barton Creek where we surveyed is protected; however, just outside of it are numerous suburbs and shopping centers with large, bustling highways, leaving us to wonder how much of the Bracted twistflower’s historical range is now buried under asphalt and perfectly manicured lawns. 

Because the areas surrounding this species’ habitats are so populated, the number of prescribed burns has declined drastically, eliminating a key instigator for the germination of its seeds and allowing the juniper trees that were historically controlled by fire to reproduce unchecked, in some areas shading out the twistflower. Another problem these poor threatened flowers face is increased herbivory due to growing White-tailed deer populations. The number of predators such as wolves and mountain lions have declined over the years due to a variety of factors, leading to an explosion of deer in Texas. Deer eat the flowering stems of the twistflower before they produce their siliques, never giving them the chance to replenish the seed bank. 

The twistflower populations we found during our surveys were noticeably predated by insects and covered in a fungus called powdery mildew. However, since the species is surviving long enough to produce siliques, these factors seem to have only minor impacts on the overall well-being of the Bracted twistflower (U.S. Fish & Wildlife Service). As with most species faced with small populations, low genetic diversity is also a concern. Individuals that share much of their genetics are susceptible to the same diseases or environmental changes, making it very easy for a singular event to wipe out an entire population. 

Conservation Opportunities

Humans have so negatively impacted the habitat of the Bracted twistflower that it now requires human intervention and monitoring in order to survive. Deer exclusion fences around some known populations, trimming and control of juniper trees, attempts to reintroduce cultivated individuals (unsuccessfully thus far), continued surveys of known populations to monitor their wellbeing, and education of the public are all being carried out by dedicated conservationists and volunteers like A Rocha USA (U.S. Fish & Wildlife Service). We can only hope that it is enough and that as a society, we learn a lesson in restraint and pursue understanding of an ecosystem over development and luxury.

A Rocha USA is supporting annual surveys of known Bracted twistflower populations. This past spring, in collaboration with staff from the Balcones Canyonlands Refuge, we didn’t manage to discover new colonies of the Bracted twistflower, but we did find a record-high abundance within old colonies, identifying over a thousand twistflowers in a single day. One good year doesn’t necessarily mean more will follow, but we were encouraged to find so many of those tousled purple petals. Despite its many threats, the Bracted twistflower is striking in its resilience, with seeds that can remain dormant in the ground for years, emerging and thriving when conditions are finally right.

Learn more about our work in Texas here. 

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Bracted twistflower

(Streptanthus bracteatus)

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