Eryngium yuccifolium Michx.
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Basis for Listing
Eryngium yuccifolium is a native component of mesic prairies in southern Minnesota. At one time, prairies were the dominant vegetation type on the landscape of that region, but since settlement they have been systematically plowed under and replaced with crop fields. This process of land conversion was so complete that by the end of the 20th century less than one percent of the original prairies remained. Obviously, the plant species that occurred in those prairies suffered the same fate. This was especially serious for prairie obligates, such as E. yuccifolium, which are restricted to prairies (Havercamp and Whitney 1983).
Eryngium yuccifolium is a rather tall, robust plant with stout, erect stems that can reach a height of 1.5 m (4.9 ft.). The stems generally remain unbranched except near the inflorescence. The leaves are linear-lanceolate in shape with parallel veins and sharp spines on the margin. The leaves can reach 80 cm (2.6 ft.) in length and have been described as yucca-like (Trent 1938); they are one of the more distinctive aspects of this species. The small white flowers are in several dense, spherical, "bristly" heads 0.5-2 cm (0.25-0.75 in.) across. It is these flowering heads rather than the individual flowers that catch your attention. The entire plant often seems to have a bluish or gray-green color.
Eryngium yuccifolium has a rather broad geographic range in North America, ranging east to Connecticut, south to Florida, west to Nebraska, and north to Minnesota. Over the entirety of its range it occupies a variety of habitats, but in the Midwest, including Minnesota, it occurs primarily, if not exclusively, in prairies. Soils are usually glacial tills and range from dry to moist. Most commonly, the plant is found on deep mesic loam but occasionally it is also found on well-drained, sand-gravel substrates.
Biology / Life History
Eryngium yuccifolium is a perennial prairie species that reproduces only by seed. It flowers from mid to late summer and is pollinated by a number of common, non-specialized prairie insects (Molano-Flores 2001). The seeds themselves posses no specialized dispersal structures, although the bristly bracts that subtend the flowers indicate the seeds may be dispersed in the fur of mammals. A study in a tallgrass prairie in Illinois (Johnson and Anderson 1986) found E. yuccifolium to be one of the most abundant species in the seed bank. General observations indicate that individual plants are long-lived, and that established populations in high-quality habitats are stable over periods of decades.
Conservation / Management
The physical appearance of E. yuccifolium is quite unique, reminiscent of a yucca or agave. For this reason it is popular as a garden plant, and it is becoming increasingly common in commercial seed mixes that are used to create or recreate "prairies". These plantings are usually done for interpretive purposes, general land conservation purposes, or sometimes as wildlife habitat. All this is good and desirable, but the value of such plantings from the perspective of preserving genetic diversity of isolated populations of rare plants is questionable.
Conservation Efforts in Minnesota
There are several prairie remnants in southeastern Minnesota that harbor populations of E. yuccifolium. A few of these tracts are managed for the benefit of the native prairie plant community. This management, at its best, appears to be maintaining E. yuccifolium in stable numbers although there are no census counts or monitoring plots to detect long-term trends.