Rare Species Guide

  Basis for Listing

Poa wolfii (Wolf’s bluegrass) is currently known to occur in 10 east-central states (NatureServe 2024). It is considered vulnerable or imperiled in all but one. Its status in Minnesota was unclear until a careful reexamination of all available evidence, including a critical study of herbarium specimens, concluded that P. wolfii is extremely rare in Minnesota. Only one authentic occurrence can be credited. It is a discovery by the eminent botanist C. O. Rosendahl in Houston County in1902. Despite the lack of recent evidence, it seems likely that P. wolfii still exists in Minnesota. There are approximately 15 species of Poa in Minnesota. They can be very difficult to identify, especially during a typical field survey, so it is possible that P. wolfii has been overlooked. Although there has been a significant decline in P. wolfii habitat since the last time it was seen in Minnesota, there are still pockets of suitable habitat that have not been investigated by an experienced botanist. Poa wolfii was listed as a special concern species in Minnesota in 1984.

  Description

Field recognition: Because of the well-known morphological and taxonomic complexity of the genus Poa, it might not be practical for anyone other than a well-prepared botanist to make a positive identification in the field. Hopefully, that will not prevent attempts to relocate this species in Minnesota. Any native Poa growing in a forest interior in southeastern Minnesota could be either P. wolfii or P. sylvestris (woodland bluegrass). Both of which would be notable discoveries. Poa palustris (fowl bluegrass) is a common look-alike that will be encountered much more often. Although other possibilities exist, a simplified key to these three species is included below (Poa pratensis - Kentucky bluegrass - is included to help avoid the most obvious mistake):

1a. Plants possessing conspicuous rhizome………. P. pratensis

1b. Plants lacking rhizomes.

2a. Lemmas with hairs on the veins, but not between the veins.

3a. Lemmas 2-3 mm long; lower branches of panicle numbering 2-9 at a node; ligules often more than 2.5 mm long………. P. palustris

3b. Lemmas 3.2-4.5 mm long; lower branches of panicle mostly 2-3 at a node; ligules not more than 2.5 mm long ………. P. wolfii

2b. Lemmas with hairs on the veins and also between the veins (the hairs between the veins are very fine, white, and may be sparse – look carefully)………. P. sylvestris

Technical description: Plants perennial; not rhizomatous, not stoloniferous, loosely tufted. Basal branching mainly pseudointravaginal. Culms 25-90 cm. Sheaths closed for 1/2 - 3/4 their length, smooth or sparsely scabrous, margins not ciliate; ligules 0.3-2.1 mm, smooth or sparsely scabrous, truncate to obtuse, ciliolate; blades 0.6-3.5 mm  wide, flat. Panicles 7.5-15(18) cm,  lax, pyramidal, open, sparse; nodes with 1-3(5) branches; branches 3-8 cm, ascending, straight to spreading, angled, angles prominent, scabrous. Spikelets 4-6.5 mm,  laterally compressed; florets 2-5; rachilla internodes to 1 mm, smooth, glabrous. Glumes 1/2-1/3 the length of the adjacent lemmas, distinctly keeled, keels scabrous; lower glumes subulate to narrowly lanceolate, (1)3-veined; upper glumes shorter than or subequal to the lowest lemmas; calluses webbed; lemmas (2.5)3.2-4.7 mm, lanceolate, green, distinctly keeled, keels and marginal veins long-villous, hairs extending up almost the whole keel length, lateral veins prominent, intercostal regions smooth, minutely bumpy, usually glabrous, rarely sparsely softly puberulent, apices acute, blunt, or pointed, white, not bronze; palea keels softly puberulent at mid-length, apices scabrous; anthers (0.5)0.8-1.2(1.5) mm. (Soreng 2007).

  Habitat

Little is known for certain about where P. wolfii is likely to be found in Minnesota. From what we do know, the most likely habitat is in a southern mesic maple-basswood forest in the rugged “blufflands” region (Rochester Plateau Subsection) in the southeastern corner of the state. It will likely be in dense shade under an unbroken canopy of mature trees such as Acer saccharum (sugar maple) and Tilia americana (basswood). Understory trees will likely be few and widely scattered, composed mostly of Ostrya virginiana (ironwood). Ideally, invasive shrubs such as Rhamnus cathartica (common buckthorn) will be absent. Soils will likely be moist, non-acidic loam, which will have a significant humus component. Previous reports of P. wolfii favoring cliffs in Minnesota are based on erroneous herbarium specimens that have since been attributed to a similar species.

  Biology / Life History

Poa wolfii is a perennial of indeterminate growth. Like most grasses, the flowers are assumed to be wind pollinated. It reproduces only by seeds, which are quite small, only about 1 mm (0.04 in.) long, and when mature, drop to the ground near the parent plant. They are likely moved short distances by small seed-foraging mammals and insects, and possibly longer distances by birds. Although P. wolfii can become established in a previously unoccupied habitat, it is not aggressive and will not easily migrate any great distance.

  Conservation / Management

Current recommendations are to maintain an intact forest community with its full complement of native species. Preserving an intact canopy will be essential, though it seems likely that a healthy, viable population of P. wolfii will not be compromised by a small canopy gap that may occur when a tree falls.

  Best Time to Search

Best time to search for Poa wolfii is when the spikelets are mature, in the last two weeks of June and all of July.

  Authors/Revisions

Welby R. Smith (MNDNR), 2008, 2026

(Note: all content ©MNDNR)

  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.