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Physaria filiformis

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Physaria filiformis (syn. Lesquerella filiformis) is a rare species of flowering plant in the mustard family known by the common names Missouri bladderpod and limestone glade bladderpod. It is native to Missouri and Arkansas in the United States.<ref>Biota of North America Program 2014 county distribution map</ref> It was federally listed as an endangered species in 1987 and it was downlisted to threatened status in 2003.<ref name=tnc>Lesquerella filiformis. The Nature Conservancy.</ref>

Physaria filiformis is an annual herb producing several slender, branching stems up to 25 centimeters (10 inches) tall, growing erect or drooping. The leaves vary in shape, and the basal ones reach 2.4 centimeters (0.96 inch) in length. The inflorescence is a raceme of pale yellow flowers with petals half a centimeter to nearly one centimeter (0.4 inch) long. The fruit is a spherical silique.<ref name=fna>Physaria filiformis. Flora of North America.</ref> The plant is a winter annual, sprouting and forming a basal rosette of leaves in the fall and then producing stems and flower the following spring.<ref name=cpc>Lesquerella filiformis. Center for Plant Conservation.</ref> Seeds are dispersed on the wind and in surface runoff.<ref name=cpc/>

Physaria filiformis grows in limestone glades and outcrops of bare bedrock in southwestern Missouri and northwestern Arkansas.<ref name=cpc/> The surrounding habitat may be prairie and pasture.<ref name=tnc/> Several types of forest may be adjacent to the glades.<ref name=young>Young, C. C., et al. (2009) Habitat relationships and management implications for Lesquerella filiformis Rollins (Missouri bladderpod) on a xeric limestone prairie. Journal of the Torrey Botanical Society 136(2) 233-41.</ref> The soil is shallow on the glades and supports few other plants. The plant grows less often in more vegetated areas with deeper soils, probably because other plants successfully compete with it there. It is also less abundant in the shady understory of Juniperus virginiana forest, as sunlight is a limiting factor in its growth. It can be found in a number of microhabitats, a factor that is important in its management and conservation.<ref name=young/> Wildfire is important in the maintenance of the limestone glade habitat and even more so its surrounding ecotones. Fire is the mechanism that keeps these habitats open and free of large and woody vegetation that shade out small annuals.<ref name=tnc/> Fire prevents ecological succession in the open habitat where the plant grows. Other plants in the local habitat include Arenaria patula, Camassia scilloides, Nothoscordum bivalve, Opuntia humifusa, Satureja arkansana, Tradescantia tharpii, and Verbena canadensis.<ref name=cpc/>

As the health of the local ecosystem depends on fire, the practice of fire suppression has caused the degradation of the habitat. When fire is prevented, woody vegetation moves in, covering the glades and blocking the light from reaching this small plant.<ref name=tnc/> This encroachment of surrounding vegetation is a main threat to the species.<ref name=cpc/> Other threats include off-road vehicles, limestone mining, and urban development.<ref name=cpc/> Invasive species of plants have been introduced to the habitat, including Bromus tectorum, a competitive grass. The plant may be affected by grazing, trampling, and other disturbance, but these threats are mild because the plant can tolerate light disturbance.<ref name=tnc/>

When Physaria filiformis was designated an endangered species there were nine populations.<ref name=fed>USFWS. Determination of endangered status for Lesquerella filiformis (Missouri Bladder-pod). Federal Register January 8, 1987.</ref> Extensive surveys located more occurrences and many of these were put under the protection of a number of agencies, including the National Park Service and The Nature Conservancy. By 2003 there were about 60 populations and the outlook for the plant had improved enough to warrant its downlisting to threatened status.<ref name=tnc/>

Most occurrences of the plant are in southwestern Missouri. A large population can be found at Wilson's Creek National Battlefield.<ref name=young2>Young, C. C., et al. (2008). Monitoring Lesquerella filiformis Rollins (Missouri bladderpod): Application and evaluation of a grid-based survey approach. Natural Areas Journal 28 370-78.</ref> Conservation activities include protection of the habitat in public areas, prescribed burns to replace the natural fire regime, and reduced use of herbicides.<ref name=cpc/>

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