McALLEN, Texas (Border Report) — Despite protests from the State of Texas, the federal government has listed as endangered a rare milkweed plant that monarch butterflies thrive on and is designating miles of critical habitat on the South Texas border that could affect future state border wall development.

The prostrate milkweed (Asclepias prostrata) on Tuesday was listed as an endangered species in the Federal Register by the U.S. Fish and Wildlife Service under the Endangered Species Act.

The federal agency has deemed 661 acres as critical habitat for the rare plants in rural Zapata and Starr counties on the border where the State of Texas has built, and is attempting to build more miles of state-funded border wall.

Crews build state-funded border wall in Los Indios, Texas, on Jan. 30 as Texas Gov. Greg Abbott announces more miles of border barrier planned and a new ‘border czar.’ (Sandra Sanchez/Border Report File Photo)

The ruling was made after the federal agency says it determined that border wall construction and enforcement activities have contributed to the decline of the rare plants in the Rio Grande Valley.

U.S. Fish and Wildlife Service also blamed invasive grasses, utility and road construction, root-plowing due to development and farming, and genetic consequences of small population size for the decrease in plants, according to the Federal Registry.

“We have determined … habitat loss from border security development and enforcement activities,” the agency wrote.

A species of milkweed grown at the National Butterfly Center in Mission, Texas. (Sandra Sanchez/Border Report File Photo)

The ruling came after Texas Attorney General Ken Paxton in April sent a letter to the agency asking them not to deem the prostrate milkweed as endangered because it could affect future border security initiatives along the Texas/Mexico border.

“We recognize the value in protecting animal and plant species native to Texas as well as the general benefit of conservation efforts. But the decision to designate critical habitat requires more than merely determining that the prostrate milkweed species is at risk. The designation determination must also account for the potential implications to border security, which implicates national security, Texas’s security and economy, and other public policy priorities, such as combatting human and drug trafficking, which are rampant in areas near the border,” Paxton wrote.

Nevertheless, the federal agency 10 months later said it had enough reasons to list the plant as “endangered.”

But it indicated that plants found on private lands would not be subject to the ruling.

And given that the State of Texas is acquiring private land to build segments of border wall in Zapata and Starr counties, it is unclear whether the state will be able to continue building on private land where prostrate milkweed exists.

But if that were to happen, Russ McSpadden, of the Center for Biological Diversity, said his nonprofit and others dedicated to conservation would consider legal options to stop construction.

“If the state decided to start construction of border wall, within critical habitat of this endangered milkweed then the Center for Biological Diversity would certainly look very closely at any legal challenges to bring forth to stop the construction of the wall,” McSpadden told Border Report on Tuesday.

McSpadden said the prostrate milkweed only grows within 9 miles of the border in the United States. He says the plant is integral to the survival of monarch butterflies.

A monarch butterfly in Toluca, Mexico, in 2006 alights on a milkweed during the breeding process. (SUSANA GONZALEZ/AFP via Getty Images)

In July, the monarchs were listed as s threatened species by the International Union for Conservation of Nature.

“Monarch butterflies migrate to this area across the Rio Grande Valley, between Mexico United States every year. So listing the prostrate milkweed on the endangered species list was the right decision. It’ll help monarchs and other pollinators to survive,” McSpadden said.

“In the spring, female monarchs will migrate north across the borderlands, and they have to find milkweed to lay eggs on where they die. And so the prostrate milkweeds are the first species that they’ll come across. The female can lay their eggs on the milkweed and then they die and the new butterflies that emerge from this will continue the migration to points further north. So these really are critically important flowers, and make the entire butterfly migration process possible,” McSpadden said.

These really are critically important flowers, and make the entire butterfly migration process possible.”

Russ McSpadden, Center for Biological Diversity

Only 24 populations of the plant survive, in South Texas and northern Mexico, where they serve as an important food source for pollinators like bees and imperiled monarch butterflies, according to the Center for Biological Diversity.

Texas Gov. Greg Abbott has named a state border czar and the Texas Facilities Commission has issued nearly $1 billion in state-funded contracts for border wall development throughout the border with Mexico. This includes the building of 9 miles of border wall in Zapata and Webb counties.

Zapata County Judge Joe Rathmell, an opponent of border wall construction, told Border Report on Tuesday that he was unaware of the ruling.

The ruling takes effect on March 30.

A 1.7-mile state-funded border wall was built in 2022 in rural Starr County, Texas. (Sandra Sanchez/Border Report File Photo)

He said the state has put up some chain link fences in areas where Zapata County ranchers have granted them rights of way. But it is all on private property.

He also says he doesn’t know what prostrate milkwood looks like. But he said if it stops border wall construction then he welcomes it.

“Anything that stops border wall consideration would be helpful,” Rathmell said.

There are over 100 different species of milkweed in North America. Prostrate milkweed grows low to the ground with stems up to 16 inches long.

The National Butterfly Center is located in Mission, Texas, on the Rio Grande. (Sandra Sanchez/Border Report File Photo)

Monarchs and other butterflies lay their eggs on the milkweed as they migrate, said Marianna Treviño Wright, executive director of the National Butterfly Center in Mission, Texas.

She says the monarchs depart in the fall and re-enter n the spring.

“They have to be able to find milkweed at every place along the journey,” she told Border Report.

The zizotes milkweed is the species most commonly found in eastern parts of the Rio Grande Valley in Hidalgo and Cameron counties where soil has more clay. But prostrate milkweed is found in sandy soil farther west in Starr and Zapata counties.

Treviño Wright is an ardent opponent of any form of border wall.

As for stopping future federal border wall construction, however, she doubts that designating the prostrate milkweed as endangered will have any effect. That’s because it would be up to the federal government to enforce the Endangered Species Act.

But if the Biden administration decides to build more wall, or if the Republican-led Congress votes to approve more funds for federal border wall construction, then the Homeland Security Secretary can waive provisions of the Endangered Species Act through the REAL-ID Act of 2005, for issues involving national security. This act has been used dozens of times to exempt federal border wall construction from areas where species are deemed endangered.

And according to the Federal Registry, this can also be used by the federal government “to waive other federal laws, including the Endangered Species Act, to expedite construction of border barriers.”

This includes areas where the prostrate milkweed grows.