Eryngium yuccifolium Michx.
Basis for Listing
Eryngium yuccifolium (rattlesnake master) 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 prairie 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, that are restricted to prairies (Havercamp and Whitney 1983).
Efforts have been made to identify and protect even tiny scraps of remaining prairie habitat, especially those that harbor sensitive or specialized species like E. yuccifolium. However, results have been mixed. Many of the remnants are so small they need constant attention to protect them from aggressive non-native plant species that can easily overwhelm the natives. The worst invaders are the sod-forming grasses like Bromus inermis (smooth brome) and Poa pratensis (Kentucky bluegrass), but there are a host of others. Encroaching brush is also a serious problem that requires ongoing management. Eryngium yuccifolium was listed as a special concern species in Minnesota in 1984.
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.
Long-term preservation of E. yuccifolium is best undertaken in its natural habitat with the full complement of associated plant and animal species, including pollinators, seed dispersal agents, and mycorrhizal fungi. However, this requires a commitment to mitigate the loss of natural ecosystem functions that so often plague small, isolated habitat remnants. Such mitigation might include prescribed dormant season burns, manual cutting of encroaching brush, hand removal of exotic species, constructing fences or barriers to discourage vehicular trespass, creation of buffers of native vegetation to minimize "edge effects", and prevention of herbicide drift from adjacent properties. Many of the remaining populations are located in strips of prairie in the rights-of-way of active and abandoned railroad lines and county and township roads. These areas may require additional conservation measures such as altering mowing patterns and curtailing herbicide use. Continuing efforts to work with railroad companies and road authorities to address these concerns would be desirable.
Best Time to Search
Searching for E. yuccifolium is made relatively easy by the large and distinctive leaves, which can be seen as early as mid-May and are fully developed from July through October. Although distinctive, flowers or fruits are not needed to make a positive identification.
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.
References and Additional Information
Havercamp, J., and G. G. Whitney. 1983. The life history characteristics of three ecologically distinct groups of forbs associated with the tallgrass prairie. American Midland Naturalist 109(1):105-119.
Johnson, R. G., and R. C. Anderson. 1986. The seed bank of a tallgrass prairie in Illinois. The American Midland Naturalist 115:123-130.
Molano-Flores, B. 2001. Reproductive biology of Eryngium yuccifolium (Apiaceae), a prairie species. Journal of the Torrey Botanical Society 128(1):1-6.
Trent, J. A. 1938. Eryngium yuccifolium: Ecological distribution and some morphological irregularities. Transactions of the Kansas Academy of Science 41:155-161.