Rare Species Guide

  Basis for Listing

Poa wolfii is distributed from Arkansas to northern Minnesota and from Illinois to Ohio, with disjunct occurrences in Virginia (NatureServe 2011). In Minnesota, it is found primarily in the southeastern corner of the state. There are historic collections from Gooseberry Falls State Park in Lake County (1938) and Itasca State Park in Clearwater County (1958), but all recent occurrences are from the southeastern-most counties. The majority of the records are from Fillmore County.

Poa wolfii appears to be naturally rare in Minnesota and throughout its range, but the reasons why are not clear. Loss of habitat is probably not the main reason, since it is found almost exclusively on cliffs in Minnesota, although some loss of habitat has occurred. Fewer than 25 populations are known in the state and all have low numbers of individuals. Given the small size and isolated, disjunct nature of its populations, P. wolfii was listed as a special concern species in Minnesota in 1984.

  Description

Poa wolfii is a perennial bluegrass, a genus of cool-season grasses typically flowering in late spring or early summer. The bluegrasses tend to be slender, with relatively narrow leaves. Leaf tips are shaped like the prow of a boat. Poa wolfii grows in loose tufts, without rhizomes and stolons. The spikelets are laterally compressed and the glumes are distinctly keeled (Soreng 2007). Closely related Poa species in Minnesota include P. sylvestris (woodland bluegrass), P. paludigena (bog bluegrass), P. alsodes (wood bluegrass), and P. saltuensis ssp. saltuensis (pasture bluegrass).

Poa wolfii grows from 25 cm (9.8 in) to 90 cm (3.0 ft.) tall. Leaf blades are 0.6 to 3.5 mm (0.02-0.14 in.) wide (Soreng 2007). The ligule is less than 2.0 mm (0.08 in.) long (Allison 1959). The flowering head (panicle) is 7.5-15.0 cm (3.0-5.9 in.) tall, and pyramidal, with an open, sparse arrangement of panicle branches. Panicle nodes have mostly 1-3 branches or sometimes up to 5 branches (Soreng 2007). The lemma is 3.5-4.5 mm (0.14-0.18 in.) long (Allison 1959); the backs of the lemmas are pubescent on some of the veins, but glabrous between veins (Allison 1959; Soreng 2007).

Even experienced botanists can have difficulty distinguishing this species from other members of the genus, especially P. sylvestris. Therefore, whenever possible a specimen should be preserved and checked by an authority familiar with the genus. Poa wolfii differs from P. sylvestris in having larger spikelets (thus larger lemmas); fewer panicle branches per node (examine lower branches); and lemmas that are usually glabrous between the veins (Allison 1959; Soreng 2007).

  Habitat

Across its range, P. wolfii is found in a variety of forested habitats, sometimes on slopes, cliffs, banks, or outcrops. Recent records in Minnesota are from the upper drainages of the major rivers of the Blufflands ecological subsection. Bedrock is exposed in river and stream valleys of the subsection and cliff faces are common. Almost all occurrences of P. wolfii in Minnesota are found on cliffs and talus.

In southeast Minnesota, P. wolfii was most commonly found on mesic cliffs, but also on several other types of cliffs and algific talus. Mesic cliff habitats are lichen and moss-dominated, shaded, and northwest- to east-facing. Dry cliffs are lichen-dominated, on dry, sunny south- to west-facing cliffs. Most of the P. wolfii occurrences were on northeast to northwest facing cliffs, but a few were found on south-facing (dry) cliffs. Within these cliff habitats, P. wolfii grows in crevices and on ledges where soil accumulates (Minnesota DNR 2005). Most occurrences were in full or partial shade but in at least one case P. wolfii was found growing in full sun. Associated species include those that are typical of mesic cliff communities such as Cystopteris spp. (fragile and bulblet ferns), Pellaea glabella ssp. glabella (smooth cliff brake), several other ferns, and several other Poa species including P. pratensis ssp. pratensis (Kentucky bluegrass) and P. compressa (Canada bluegrass).

The historical locations of P. wolfii from Gooseberry Falls State Park and Itasca State Park were found in rocky crevices of a Lake Superior cliff and in a "swampy area", respectively. Neither of these populations has been relocated.

  Biology / Life History

Little is known about the life history or specific habitat requirements of P. wolfii. It is wind pollinated and apparently relies on seeds for reproduction. Since it usually grows on cliffs in Minnesota, it may require specialized habitat conditions. Schwegman (1991) reports that the species disappears rapidly after flowering except for a tuft of sterile leaves.

The best time to search for P. wolfii is in June and July when the plant is flowering and fruiting.

  Conservation / Management

There are several potential threats to cliff habitats. Agricultural and silvicultural land uses such as grazing and logging can affect cliff communities. When the tree canopy adjacent to a cliff is removed, the exposure of the cliff face to the sun could be increased. This may induce physiological stress to cliff-dwelling plants, especially on shaded mesic cliffs. Development, such as quarrying and the construction of roads, can directly impact cliff habitats by removal of the rock substrate that is the basis of the habitat. Erosion from upslope areas that have been cleared or otherwise altered can affect soils or water that move down the cliff face. Recreational uses such as hiking or rock-climbing and scrambling on cliff faces can easily damage the fragile plant assemblages that occur on cliffs. The best way to protect P. wolfii in Minnesota is to protect the cliff habitats where it occurs or has the potential to occur.

Logging projects near cliffs should be evaluated for their potential impact on the cliff habitat. Roads and trails can be routed away from sensitive areas and rock climbing should be prohibited on cliffs where rare plant populations are present.

  Conservation Efforts in Minnesota

The Minnesota Biological Survey has been completed in the range of P. wolfii, and at least 10 of the most recent records were discovered during this inventory effort. About half of the known records in Minnesota are on state-owned lands. Where the potential exists for human disturbance on these lands, special protection should be afforded to P. wolfii and its rare habitat. Habitat protection needs for the species should be incorporated into resource management plans.

  References and Additional Information

Allison, H. 1959. Key to the grasses of Minnesota found in the wild or commonly cultivated as crops. Department of Botany, University of Minnesota, Minneapolis, Minnesota. 52 pp.

Minnesota Department of Natural Resources. 2005. Field guide to the native plant communities of Minnesota: the eastern broadleaf forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 394 pp.

NatureServe. 2011. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia. . Accessed 5 January 2011.

Schwegman, J. E. 1991. New records for Illinois vascular plants. Erigenia 11:9-12.

Soreng, R. J. 2007. Poa sect. Sylvestres. Pages 510-514 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 24. Oxford University Press, New York, New York.