Synonyms

Mammillaria vivipara, Escobaria vivipara

  Basis for Listing

Coryphantha vivipara (ball cactus) is one of only three species of cacti native to Minnesota, and it is by far the rarest. It ranges across the Great Plains, but occurs only where substantial amounts of bedrock is exposed at the surface. It was discovered in Minnesota in 1898 by Lycurgus Moyer, the species was described as quite abundant at sites in the Minnesota River Valley (Minnesota River Prairie Subsection) in Big Stone County and adjacent portions of Lac Qui Parle County (Moyer 1899). When this cactus was listed as state threatened in 1984, the only known surviving plants were small remnants of the original population. The thin-soiled prairies that harbored the original populations had largely been converted to agricultural use, greatly diminishing available habitat. Extant C. vivipara plants are scattered infrequently among granite outcrops in a 5-8 km² (2-3 sq. mi.) area.

Only a portion of the single C. vivipara population occurs on protected public land. The majority occurs on adjacent private land, where remaining habitats are being rapidly destroyed by granite quarrying. Because it is clearly one of the rarest species in the state, and because the existing population is known to be threatened by both quarry operations and illegal collecting by cactus fanciers, C. vivipara was afforded state endangered status in 1996. 

  Description

There may be as many as 7 varieties of this species in North America, some of which have been described as separate species (Benson 198342). The population in Minnesota belongs to the typical variety that is characteristic of grasslands in the Great Plains. The appearance of C. 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. Coryphantha vivipara is round (hence its common name) with spiny tubercles and brilliant red or purple flowers at the tips of the stem (Benson 1983). Flowers mature into brown fleshy brown fruits the following spring and contain 50-—100 seeds each. This species can grow in clumps up to 60 cm (24 in.) in diameter.

  Habitat

Coryphantha 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 O. fragilis (brittle prickly pear) cactus.

  Biology / Life History

Coryphantha vivipara is a leafless perennial 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.

The specific epithet of ball cactus, “vivipara”, was given in recognition of a rare form of reproduction that exists in very few cacti. The process is called vivipary and happens when the seeds germinate within the fruit and subsequently develop before the seeds are dispersed from the parent plant.

In other words, when a mature fruit, which is thick and fleshy, is broken open, the contents may reveal young developing cactus plants rather than seeds. However, the developing offspring may be the product of asexual reproduction and would therefore be considered a product of pseudovivipary (Cota-Sanchez 2004). This is presumably an adaptation to the harsh, semi-arid environment that ball cactus inhabits.

  Conservation / Management

Coryphantha vivipara is known to be very sensitive to fire (Thomas and & Goodson 1992; Thomas 2006). Unlike prairie grasses, C. vivipara will be killed by fire, and it will not resprout from the roots. This is perhaps the reason it is limited to habitats where the vegetation is too sparse to carry a wild fire. Even then, it is vulnerable from radiant heat generated by a hot prairie fire, especially where its habitat might grade into a habitat with enough dry fuel to carry a fire. At least one prescribed burn in Minnesota 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 is a serious issue that has already destroyed much habitat that was occupied by C. vivipara, and the threat continues today. There is no way by which C. vivipara can survive when its habitat is quarried, and transplantation of threatened individuals does not further the cause of long-term conservation.

  Best Time to Search

Because this species is evergreen, Coryphantha vivipara can be seen and identified any time of the year except when covered by snow.

  Conservation Efforts in Minnesota

State endangered status was afforded to C. 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 C. vivipara.

  Authors/Revisions

Welby R. Smith (MNDNR), 2020

(Note: all content ©MNDNR)

  References and Additional Information

Benson, L. 1983. Cacti of the United States and Canada. Stanford University Press, Redwood City, California. 1044 pp.

Cota-Sanchez, J. H. 2004. Vivipary in the Cactaceae: Its taxonomic occurrence and biological significance. Flora 199(6): 481-490.

Moyer, L. R. 1899. Extension of plant ranges in the upper Minnesota valley. Pages 191-192 in C. Macmillan, editor. Minnesota Botanical Studies. Volume II. Botanical Series Number IV. Geological and Natural History Survey of Minnesota, Minneapolis. 780 pp.

Thomas, P. A. 2006. Mortality over 16 years of cacti in a burnt desert grassland. Plant Ecology 183:9-17.

Thomas, P. A., and P. Goodson. 1992. Conservation of succulents in desert grasslands managed by fire. Biological Conservation 60(2): 91-100.