Escobaria vivipara (Nutt.) Buxbaum
Click to enlarge
Coryphantha vivipara, Mammillaria vivipara
Basis for Listing
Escobaria vivipara is one of only three species of cacti native to Minnesota, and it is by far the most rare. Discovered in 1898 by Lycurgus Moyer, the species was described as quite abundant at sites in the Minnesota River valley in Big Stone County and adjacent portions of Lac Qui Parle County (Moyer 1898). When this cactus was listed as state threatened in 1984, the only known surviving plants were remnants from the original population. The thin-soiled prairies harboring the original populations had largely been converted to crop production, greatly diminishing available habitat. Extant E. vivipara plants are scattered infrequently among granite outcrops in a 5-8 km² (2-3 mi.²) area.
There may be as many as 7 varieties of this species in North America, some of which have been described as separate species (Benson 1982). The population in Minnesota belongs to the typical variety that is characteristic of grasslands in the Great Plains. The appearance of E. vivipara is distinctly that of a cactus and it can be easily identified. The other 2 cactus species in Minnesota are of the genus Opuntia (prickly pear cactus) that have flattened, jointed stems and yellow flowers. Escobaria vivipara is round (hence its common name), with spiny tubercles and brilliant red or purple flowers at the tips of the stem (Benson 1982). Flowers mature into fleshy brown fruits the following spring. This species can grow in clumps up to 60 cm (24 in.) in diameter.
Escobaria vivipara occurs locally in crevices of granite outcrops and in thin soil over granite bedrock. The Minnesota population was originally more extensive than it is now and probably occurred in adjacent prairie habitat before agricultural conversion. It occurs with the widespread and adaptable Opuntia fragilis (brittle prickly pear) cactus.
Biology / Life History
Escobaria vivipara is a perennial, leafless plant. All of the work of food manufacture and storage is carried out in the fleshy stems. New growth, including branches, flowers, and spines, appears in small distinct areas called areoles. The areole is regarded as a modified axillary bud and the spine a specialized leaf. Besides affording protection from herbivores, the many spines on the stem assist in vegetative propagation by animal dispersal. Many species of the cactus family are pollinated by bees, beetles, birds, bats, and moths at the time of flowering (Zomlefer 1994). Escobaria vivipara flowers and fruits on the new growth of the current season (Great Plains Flora Association 1986).
Conservation / Management
Escobaria vivipara is very sensitive to fire. At least one prescribed burn that was intended to facilitate management of adjacent prairie habitat killed several plants and severely damaged several others. There is no season of the year when fire is safe; plants must be protected from fire at all times. Granite quarrying can also result in the complete destruction of E. vivipara and its habitat.
Conservation Efforts in Minnesota
State endangered status was afforded to E. vivipara in 1996 after a survey of its habitat by the DNR's Minnesota Biological Survey revealed threats to the existing population by granite quarry operations. The portion of the population located on a National Wildlife Refuge is protected from granite quarrying, but is still potentially threatened by cactus poachers. Prescribed burning of occupied habitat must be carefully managed to avoid damage to E. vivipara.
References and Additional Information
Benson, L. 1982. The Cacti of the United States and Canada. Stanford University Press, Stanford, California. 1044 pp.
Great Plains Flora Association. 1986. Flora of the Great Plains. University Press of Kansas, Lawrence, Kansas. 1,402 pp.
Moyer, L. R. 1898. Extension of plant ranges in the Upper Minnesota Valley. Minnesota Botanical Studies 1:191-192.
Zomlefer, W. 1994. Guide to Flowering Plant Families. University of North Carolina Press. Charlotte, North Carolina. 424 pp.