Endangered and Threatened Species of Michigan:
Cultivating Rare Plants*

The W. J. Beal Botanical Garden  is an internationally recognized plant science garden with a long history of commitment to formal and informal education. The entire garden has been established with a system of interpretive labels installed for each plant on display. It currently includes nearly 2,000 species arranged in 94 intensely maintained beds that comprise a portion of 5 main collections: systematic, economic, ecological, landscape plants, and endangered and threatened species of Michigan. The completion of the endangered and threatened species collection is due to a cooperative effort between Michigan state government, Michigan Natural Features Inventory and Michigan State University. It serves as a conservation education tool for the University and general public. The collection currently includes 44 species with representation in each endangerment category. Development of this special collection is discussed and characteristics of selected species growing in their natural habitat are contrasted with specimens under cultivation in the garden, with special attention devoted to 3 federally threatened herbaceous perennials endemic to the Great Lakes shoreline: Cirsium pitcheri, Iris lacustris, and Solidago houghtonii.
 

The endangered and threatened (ET) species collection, like the rest of the Garden, is used for educational purposes. It is not intended to "save" species but instead serves as a conservation awareness tool and an identification resource. The educational objectives of this collection are:
 

1) to make people aware that ET species exist both in Michigan and on a national level
2) to clarify and define the endangerment categories
3) to explain why Michigan contains rare plants and promote their conservation
4) to inform people where in the state they occur through interpretive labeling.

All 94 Garden beds, including the ET site, are situated in the flood plain of the Red Cedar River. The site chosen for the ET living collection was amended with sand to improve drainage. It consists of a curved, sloping bank with southeastern to southern and southwestern aspects at slope angles of 10-20%. Existing overstory vegetation supplies a range of sunlight intensity. Twenty-three species already cultivated in the Garden were vegetatively propagated. Nearly ½ of the collection was grown from seed started in a greenhouse. The majority of the seeds were obtained through the International Seed Exchange Program. Wild collected seed or seed whose original location could be documented was selected over material that had no documentable location. Cultural information was deduced from State Natural Heritage Program's Michigan Natural Features Inventory (MNFI) species abstracts. Plants were positioned in the garden according to their different needs for sun or shade. At each planting location leaf mold was incorporated into the surface of a 1 meter area. After plants were in place, they were mulched with a shredded, steam sterilized composted leaf mulch. The bulk of the ET living collection was planted in 1991. Two of the three Great Lakes shoreline endemics were obtained for the collection in 1993. Seed of Cirsium pitcheri was collected in June of 1993 from a wild population in MI and started in the greenhouse. The Cirsium planting location was supplemented with sand and seven seedlings were transplanted to the Garden while 12 were placed in a test plot at Beaumont Nursery. Solidago houghtonii typically grows in interdunal wetlands along the shoreline. Therefore, a single plant obtained from a wild population, was transplanted to the pond, a site away from the ET collection where continuous drip irrigation provides correct soil moisture for the cultivation of native wetland species. Seed collected in 1993 from the original S. houghtonii accession was started in a greenhouse in spring of 1994 and 12 plants were transplanted to a test plot on non-irrigated soil at Beaumont Nursery.
 

Only qualitative observations have been recorded for plants in this collection since 1993. There were few total failures, a failure being defined as death of a plant after one season. Success for plants whose predominant method of reproduction is sexual, is defined as plants that will produce viable seed or additional seedlings. Success for plants that appear to reproduce more vegetatively and less by seed, is measured by whether the plant spreads vegetatively or not. The majority of rare plants under cultivation are more robust and vigorous compared with those in their natural habitats, however, this has not been quantified for any species. Of the 3 Great Lakes shoreline endemics Cirsium pitcheri was the most robust compared to individuals growing in situ. The first year juveniles grew much larger and developed more leaves than any juveniles ever seen on sand dunes (Figure 1). All plants started from seed in 1993, regardless of planting site, flowered within 2 years, set seed, and died, as is characteristic for a monocarpic perennial. Iris lacustris showed the least difference under cultivation from that in situ. It steadily increased rhizomatously, however, few stems flowered annually and no capsules were observed since it was planted. The original plant of Solidago houghtonii has flowered and set seed annually at the pond site since planting in 1993. Seedlings have not been noted around the mature plant, however, rhizomes have developed and have been removed. Four of the 12 seedlings planted at the test plot in 1994 developed buds and began to flower in October when a killing frost halted development. All plants at the test plot developed additional rhizomes and flowered abundantly beginning in August of 1995.
 

The robust growth habit of the plants contained in the ET collection is due to the relatively rich flood plain soil of the Garden and frequent weed removal, as well as frequent irrigation. The most dramatic difference between cultivation and in situ plants was the extremely robust juveniles (Figure 1) and greatly shortened bloom time for Cirsium pitcheri which typically takes 4 to 8 years to bloom (U.S. Fish & Wildlife Service 1991). The dense mat of stems formed by Iris lacustris in cultivation is not unlike that found in full sun in its natural habitat. In shade the clones produce fewer stems farther apart than in sun (Figure 2). This taxon has been popular among rock garden or alpine plant enthusiasts and is available commercially via mail order in Oregon (Ethan Johnson, Holden Arboretum, pers. comm.). Although Iris lacustris is self-compatible, fruit set is quite low in situ (Planisek 1983), so the lack of fruit set in cultivation is not surprising. Thriving Solidago houghtonii in the test plot demonstrated that it did not require saturated soil as presumed. The shade provided by deciduous trees in mid to late afternoon was thought responsible for slight elongation of flowering plants and subsequent lodging.
 

Michigan has over 3200 miles of shoreline, ranking second only to Alaska in length of shoreline in the United States (Voss 1972). Nevertheless one of the state's most threatened habitats is the shoreline, which supports the highest concentrations of 3 Great Lakes endemics. All 3 endemic plants are propagated and cultivated with little difficulty. Consequently there is concern that "easy to grow" rare plants may be considered less worthy of protection by decision makers who might be inclined to ignore the ecological context in which protection issues must be viewed. Although reintroduction is still a somewhat controversial issue in Michigan, it is hoped the information gained through propagation and cultivation of these and other species will be useful to future reintroduction efforts. The State Natural Heritage Programs's Nongame Wildlife Fund and Living Resources Small Grant Program provided partial funding for the construction and labeling of the collection. MNFI provided editorial assistance and all photographs for the brochure produced by Beal Garden staff.
 

Planiseck, S. L. 1983. The breeding system, fecundity and dispersal of Iris lacustris. Michigan Botanist. 22:93-102 U. S.

Fish and Wildlife Service. 1991. Cirsium pitcheri (Pitcher's thistle) Recovery Plan. Agency Draft. U. S. Fish and Wildlife Service, Fort Snelling, MN. vii + 111 pp.

Voss, E. G. 1972. Michigan Flora: A Guide to the Identification and Occurrence of the Native and Naturalized Seed-Plants of the State. Cranbrook Institute of Science, Bloomfield Hills, MI 48013. Bulletin no. 55, 1972 = Part I: Gymnosperms and Monocots, 488 pp.