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CoreyW. Burt WSPGroupCanada Limited 582Lancaster St.W Kitchener, ON, N2K 1M3

JessicaA. Consiglio CreditValleyConservation 1255 OldDerry Rd. Mississauga, ON, L5N6R4

Michael J. Oldham Natural Heritage Information Centre Ontario Ministry of NaturalResources and Forestry 300Water St. Peterborough, ON, K9L 3C8

Significance of the Report. The invasive grass Microstegium vimineum (Trin.)A.Camus is reportedfor the firsttime from Canada.

Previous Knowledge. Microstegium vimineum (Trin.) A. Camus (Japanese Stiltgrass) is an annual grass native to China, India, Japan, Korea, Taiwan, Malaysia,andportionsoftheCaucasus(Ohwi1965).Ithasbeenintroducedinto other parts ofAsia and into Europe,Africa, and CentralAmerica (Weber 2003, EPPO 2020). Japanese Stiltgrass is also known as Nepalese Browntop, Nepal Microstegium,andPackingGrass.Microstegium vimineum wasfirstrecordedin North America in 1919, growing along a creek bank in Knoxville, Tennessee (Fairbrothers and Gray 1972). It has since been introduced and become established in the northeastern, southeastern, and midwestern states, as well as in Texas (USDA NRCS 2020). The closest known record of M. vimineum to CanadaislocatedinNiagaraCounty,NewYork(iMapInvasivesPresencerecord #1039405) (NatureServe 2020), which is approximately 20 km from the new Canadian population reported here, in Short Hills Provincial Park, Niagara RegionalMunicipality, Ontario.

Considered an invasive species in North America and a potential threat to economic and ecological resources, Microstegium vimineum is regulated as a pest in Canada under the Plant Protection Act (Canadian Food Inspection Agency2019). Itis capable ofinvading streambanks, floodplains, mesic woodlands, forests, swamps, and other wetlands as well as disturbed habitats like roadsides, trail edges, early successional fields, wet fields, lawns, thickets, and

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FIGURE 1:Map showingthe location of the first collection of Microstegium vimineum in Canada, indicatedbyablack starintheinset.The NorthAmericanmapprovidescontext.

gardens (Fairbrothers and Gray 1972; Hunt and Zaremba 1992; Redman 1995; Cole andWeltzin 2004; Huebner 2010). In addition to rapidly colonizing naturally or anthropogenicallydisturbed areas, M. vimineum can also become established in shaded environments (Barden 1987). It can form dense monocultures (Hunt and Zaremba 1992) and seed banks have been reported to remain viable for at least three years (Barden 1987). Additionally, field experiments have demonstratedthatM.vimineum cansuppressnativetreeregeneration(Floryand Clay2010a)andreducenativeplantbiomassandspeciesrichnessthroughdirect competition (Flory andClay2010b).

Discussion. Microstegium vimineum was observed on September 8, 2019 while botanizingin ShortHills ProvincialPark, Niagara RegionalMunicipality, Ontario(Figure1).ShortHillsProvincialParkisamosaicofnaturalandcultural vegetation communities includingdeciduous forest, woodland, regenerating old


field meadows and coniferous plantations. These communities are interspersed byextensivetrailsystemsutilizedbypedestrians,cyclistsandequestrians.Short Hills Provincial Park covers 688 ha of land which the Ontario government initiallybegan acquiringin the 1960s, andto date, approximately15% ofthe park remains active agricultural land (Ministry of Natural Resources and Forestry 2019).

The firstMicrostegium vimineum specimen was collectedin the western portion ofShortHills ProvincialPark, adjacentto the BruceTrail. It was located at the interface of an open oldfield meadow composed of cool season grasses and awoodlanddominatedbyJuglans nigra L.(BlackWalnut).Soilsintheareaappeared to be primarily comprised of sandy loam. The individuals initially encountered occurred in two dense patches. The first of these was approximately onemeterbyfour metersin area, approximatelyten meters east ofthetrail.The secondpatch was approximately20 meters northeast ofthe firstpatch, approximatelytenmetersbytenmetersinarea, situatedapproximatelytwometersfrom the trail. No individuals in either patch were observedflowering or fruiting.Associated species growing in the general area included regenerating trees and shrubs (Fraxinus pennsylvanica Marshall, Juglans nigra, and Rubus allegheniensis Porter), abundant exotic cool season grasses (Phleum pratense L., Poa pratensis L. subsp. pratensis and Dactylis glomerata L.), and forbs typical of disturbed habitats (Monarda fistulosa L., Agrimonia gryposepala Wallr., Plantago rugelii Decne., Medicago lupulina L., and Solidago canadensis L. var. canadensis).

AdditionalsearchingalongtheBruceTrailfurthernortheastoftheinitialcollection location revealed larger, contiguous patches of Microstegium vimineum thatdominatedthe groundlayer in areas adjacentto the trail, extendinginto deciduous woodland, deciduous forest, and meadow vegetation communities. The secondcollectionwasmadeinaJuglans nigra dominatedwoodland,growingin semi-shaded conditions where M. vimineum was the dominant vegetation in the groundlayer(Figure2).Severalindividualsatthislocationhaddevelopedinflorescences. Afterpreliminaryfieldsurveys,R.Gould(pers.comm.November20, 2019) confirmed that the extent of the infestation spanned several hectares of woodland,forest,andmeadowinthenorthwestportionofShortHillsProvincial Park. It shouldbe notedthatM. J. Oldham and others did not note the presence of M. vimineum during extensive botanical surveys in Niagara RegionalMunicipality in 2006, 2007, and 2008 (Oldham 2010). Additionally, in 2014 J. ConsigliovisitedthesamesectionofShortHillsProvincialParkwhereM. vimineum is now dominant anddid not observe this species.

The precise origin ofthe firstinvasion of Microstegium vimineum in Canada is currently unknown. Mehrhoff (2000) suggested seeds may be naturally dispersedby water, as the small caryopses are capable offloating, or maybecome attachedtotravellinganimals.Anthropogenicdispersalviavehiclesandclothing hasalsobeennoted(Mehrhoff2000)andislikelythereasonfortherapidspread of M. vimineum in other areas (Rauschert et al. 2009). Short Hills Provincial Park is surrounded by a network of roads, so seeds or a vegetative propagule could easilyhavebeenintroducedon vehiclestravellingfromthe UnitedStates.

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FIGURE2:AdensepatchofMicrostegium vimineum growingintheunderstoryofawoodlanddominatedby Juglans nigra.Photo byCoreyW. Burt.

Additionally, the Bruce Trail is awell-known hikingtrail whichis usedbyOntario residents aswell asAmerican visitors.

As the landscape matrix surroundingShortHills ProvincialParkis primarily composed of agricultural lands, it is possible that viable seeds of M. vimineum travelled to Canada as a contaminant in hay, forage, or other agricultural seed mixes. It is also worth noting that dumped potting soil and horticultural plant material which likely originated from adjacent private properties was observed in the northwestern portion of Short Hills Provincial Park near the largest observed patch of M. vimineum. Therefore, it is also possible that M. vimineum couldhavebeenintroducedtoShortHillsProvincialParkasasoilcontaminant.

Barden (1987) noted that Microstegium vimineum was slow to establish in areasofundisturbedvegetationbutestablishedrapidlyinanthropogenicallydisturbed areas which had been mowed. The trail system in ShortHills Provincial Park is mowed, and dense patches of M. vimineum were frequently observed along mowedtrail edges. Itis likelythat M. vimineum seeds and/or fragmented vegetativepropagulesweredispersedthroughoutShortHillsProvincialParkvia trailmowing,basedonpatchproximitytothetrailsystemandtheplant’sability to root readilyfrom the nodes.

The Canadian FoodInspectionAgency(CFIA) andOntario Parks have been notified of this sizable Microstegium vimineum population. Ontario Parks staff are workingto map and measure the exactextent ofthe populationwithin Short


FIGURE 3: Vegetative culms of Microstegium vimineum, clearly displaying the distinct line of silverhairsalongthemidvein of the blade. Photo by CoreyW. Burt.

HillsProvincialPark,andCFIAstaffwillbeconductingtargetedsurveysoutside of the park in adjacent lands.ANotice of Prohibition of Movement was issued inShortHillsProvincialParkwhichrestrictsthemovementofsoilandplantmaterial, and control measures are anticipated to take place in spring 2020 (S. Leone pers. comm. November 2019; R. Gould pers. comm. November 2019). Localbotanists shouldkeep watchfor this species in other counties and regions withinOntarioandinotherprovincestopreventfurtherestablishmentofthisinvasive grassin Canada.

Diagnostic Characters. Microstegium vimineum is asprawling annualgrass capable of growing up to 1 m in height (Gleason and Cronquist 1991; Thieret 2003;Chen andPhillips 2006). It readily roots from the nodes andforms extensivedensemats. Ehrenfeld(1999)reportedseveralpopulationsofarhizomatous, perennial form of M. vimineum; however, this is an error derived from a misidentification.Mehrhoff(2000)statedthatnoherbariumspecimenofthisallegedperennialformhadbeendepositedtoanherbarium, andthemorphological characters presented were similar to the native grass Leersia virginica Willd. One of the most notable characters of M. vimineum is the distinctline of silver

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FIGURE 4: Herbarium specimen (NHIC accession #09651) of Microstegium vimineum.

hairs along the midvein of the lanceolate leaves. Redman (1995) reported that this was absentin early season,in specimens in fruit andin flower, andin specimens growinginfull sun.Contraryto Redman’s findings,the M. vimineum observedin ShortHills ProvincialParkhad silver hairsalongthe midveinin specimens that were flowering and in specimens that had been growing in full sun (Figures 3 and 4). The inflorescences are arranged on terminal and axillary racemes and may be cleistogamous or chasmogamous (Gibson et al. 2002; Theiret 2003). Pedicels are ciliate (Gleason and Cronquist 1991) and spikelets occurinpairs,onepedicellate,theothersessile(ChenandPhillips2006).Fertile


lemmasmaybeawnedorawnless(GleasonandCronquist1991).Severalprevious authors have designated varietal status based upon the presence or absence of awns (Fernald 1950; Hitchcock 1951; Bor 1960); however, a morphological analysis of New Jersey specimens concluded that this condition is variable and that these subspecific ranks should not be recognized (Fairbrothers and Gray 1972). Specimens collected from Short Hills Provincial Park sported long, twisted awns.

Microstegium vimineum is morphologically similar to Leersia virginica and Brachyelytrum P. Beauv. species. It can be readily distinguished vegetatively frombothtaxabytheprominentlineofsilverhairsalongthemidveinoftheleaf blades. There is also a distinct phenological difference, as L. virginica and Brachyelytrum species both fruit inAugust, while M. vimineum does not begin fruiting until late September to early October (Mehrhoff 2000; Stephenson 1971).Leersia virginica hasdistinctlypubescentnodesandrhizomes withoverlapping scales whereas M. vimineum has glabrous nodes and lacks rhizomes (MICHIGAN FLORA ONLINE 2011). Brachyelytrum species have larger spikelets which are equal to or greater than 8 mm in length (Theiret 2003; MICHIGANFLORAONLINE2011), while M. vimineum spikelets are 3.7–6.6 mm long, excluding awns(Theiret2003).

Specimen Citations. ONTARIO: Regional Municipality of Niagara: Bruce Trail, Short Hills Provincial Park, Pelham. Black Walnut dominant cultural woodland. Dominant species in ground layer. Thousands of plants throughout cultural woodland. Some fruiting, mostly vegetative. First Canadian Record. 43.10204668, –79.28996053. September 8, 2019. C. Burt, J. Consiglio CBJC2019- 070 (NHIC).

ONTARIO: Regional Municipality of Niagara: Bruce Trail, Short Hills Provincial Park, Pelham. Cultural Savannah; ELC code CUS1; Black Walnut dominant.Onevegetativecolonyadjacenttrail(1¥ 4m)at17T6381034772718 and one large clump (10 m ¥ 10 m) approx. 10 m south of trail at 17T638107 4772709. A second collection was made trailside in ELC code CUW1 at 17T 639152 4773567 with some fruiting but mostly vegetative. Associated species: Fraxinus pennsylvanica, Juglans nigra, Phleum pratense, Monarda fistulosa, Agrimonia gryposepala, Rubus allegheniensis, Poa pratensis, Dactylis glomerata, Plantago rugelii, Medicago lupulina, Solidago canadensis. September 8, 2019. C. Burt, J. Consiglio CBJC-2019-067 (HAM).


Thank you to Nadia Cavallin and Joseph Mentlik who provided assistance using microscope photographysoftwareandprovidedadigitalscannedcopyoftheHAMherbariumspecimen,toEwa Kielasinska who created the location map, to Ron Gould and CFIA staff for providing additional commentsandinputonthepopulationofMicrostegium vimineum inShortHillsProvincialPark,and toDawn Renfrew for providingfeedbackonanearlierdraftofthis paper.


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