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Missing Milkweed Found in Baxter County

Arkansas Natural Heritage Commission - Wednesday, June 22, 2016

Twenty different species of milkweeds have been documented in Arkansas since records started being kept in the early 1800s, but until May of this year only 19 of the 20 could be accounted for. The missing twentieth species was narrow-leaf milkweed (Asclepias stenophylla), which was last documented from Arkansas in 1953 by Dr. Dwight Moore, then professor of botany at the University of Arkansas. Moore collected it in Carroll County as part of a study of the flora in the area to be inundated by Table Rock Lake, which was constructed from 1954 to 1958 by damming the White River in Missouri. The species has not been reported from Arkansas since, despite numerous surveys over the years.

Then, in May, ANHC botanist Theo Witsell, along with ANHC Chief of Land Acquisition and Stewardship Bryan Rupar, and Nate Weston, an intern from the University of Central Arkansas, discovered a small population in Baxter County. The three were conducting field work in dolomite glades, rare habitats consisting of open, rocky grasslands and savannas where dolomite bedrock outcrops or comes close to the surface of the ground. These habitats, which occur primarily in the White River Hills Ecoregion of the Ozark Plateau in Arkansas and Missouri, are hotspots of biological diversity and are the primary habitat for a number of rare species. Three of the plants found in these glades: Bush’s yellow coneflower (Echinacea paradoxa var. paradoxa), Bush’s skullcap (Scutellaria bushii), and Trelease’s larkspur (Delphinium treleasei), are of global conservation concern and are considered to be endemic (restricted) to the Ozark Plateau.

Dolomite glades are a habitat of conservation concern in Arkansas due in part to their species richness, but also to their rarity and to a number of threats that they face. Much of the dolomite glade habitat in Arkansas was lost between the 1940s and 1960s as a series of large lakes were constructed along the White River and its tributaries, inundating much of Arkansas’s glade country. Other threats to these habitats include invasion of open glades by woody vegetation (especially eastern red cedar, Juniperus virginiana) in the absence of fire, and also urbanization and other development around these lakes. The largest concentration of dolomite glades remaining in Arkansas occurs north of Mountain Home, in the area between Bulls Shoals Lake and Norfork Lake, though little of this habitat is formally protected.

Narrow-leaf milkweed is primarily a species of dry prairies in the Great Plains and, so far as is known, occurs in Arkansas only in open glades on dolomite bedrock in Baxter County, with sites known historically in Carroll and Marion counties. Milkweeds are important plants for many species of insects and are the larval host plants of the Monarch butterfly, a well-known species that has declined across its range in recent decades.

Photos: Top- Historical specimen of narrow-leaf milkweed (Asclepias stenophylla) collected in Carroll County on August 17, 1953. Middle - Dolomite glade habitat in Baxter County. Bottom - Narrow-leaf milkweed (Asclepias stenophylla) growing in dolomite glade in Baxter County, May 2016.

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