Assessed by COSSARO as Threatened
February 2011

Part 1: COSSARO Candidate Species at Risk Evaluation form

February 2011
Purple Twayblade (Liparis liliifolia)

Current designations:

NRANK Canada – N2
COSEWIC – Threatened (November 2010)
SARA – Endangered (Schedule 1) General Status Canada – At risk (2005) ESA 2007 – Endangered
General Status Ontario – At risk (2005)

Distribution and status outside Ontario

The distribution of this species extends from southern Ontario and Quebec, eastward to New England, westward to Minnesota and Oklahoma and southward to the upland regions of Georgia (COSEWIC 2010). This orchid is most common in the Midwestern and southern states and becomes increasingly uncommon further to the north (Mattrick 2004).

Eligibility criteria

Native status

Yes. The species has been known to occur in Ontario since 1864 (COSEWIC 2010).

Taxonomic distinctness

Yes. There are no taxonomic controversies surrounding this species, which has been consistently classified as Liparis liliifolia since 1825.

Designatable units

No morphological or taxonomic differentiation is recognized within this species, so only one designatable unit is recognized.

Priority-setting criteria

Recent arrival

No. The species has been known to occur in Ontario since 1864 (COSEWIC 2010).



Primary criteria (rarity and declines)

1. Global rank

Not in any category. The global status rank of Purple Twayblade was last assessed in 2002 as secure (G5; Nature Serve 2011).

2. Global decline

Not in any category. In regions with large areas of suitable habitat, such as in the Midwestern U.S., Purple Twayblade is increasing both in abundance and distribution, becoming more common today than historically (Sheviak 1974, Homoya 1993). In contrast, its range has shrunk in the northeast, especially New England, with the return of a more forested landscape (Mattrick 2004).

3. Northeastern north america ranks

  1. Purple Twayblade is ranked S1, S2, or SX in 53% of the 17 neighbouring jurisdictions where it is ranked (Table 1). In New England, this species is ranked in Division 2, or Regionally Rare in The New England Plant Conservation Program, as a taxon with fewer than 20 current occurrences (reported since 1970) within New England (Brumback et al. 1996).

4. Northeastern north america decline

TH. Purple Twayblades were quite common in parts of southern New England at the turn of the last century. Most of the more than 100 known populations were eliminated with changes to the landscape of New England. There has been further population losses since 1993, with only 12 of 27 relocated despite repeated searches (Mattrick 2004). This is, however, an inconspicuous orchid that colonizes successional habitats that are not typically visited by botanists.

5. Ontario occurrences

TH. According to NHIC (2011), there are 11 element occurrences, only five of which are extant. In the more recently updated status report, however, there may be as many as18 extant populations in Ontario, although only 11 of these were recorded in 2008/9. The total population in Ontario is estimated to be 100-300 individuals (COSEWIC 2010).

6. Ontario decline

Not in any category. Since fieldwork for the 1998 COSEWIC assessment (White 2001), seven new occurrences of Purple Twayblade have been discovered in Ontario. This includes two populations in which over 200 plants were recorded, but no plants were found in either location when they were last checked in 2008. It is unknown whether new populations since 2001 previously existed and were located as a result of increased search effort, or if they have been recently established. The discovery of several new populations in recent years has extended the known range of this orchid into eastern Ontario and southern Quebec (COSEWIC 2010). While some declines or disappearances of previously known populations are still evident, this may be due to natural succession, with new colonization events elsewhere making up for such perceived declines.

7. Ontario’s conservation responsibility

Not in any category. The Canadian populations in Ontario and Quebec occupy less than 10% of the global range of the species (Brodribb and Oldham, 2000).

Secondary criteria (threats and vulnerability)

1. Population sustainability

Not in any category. Although there is no information relevant for determining sustainability of Purple Twayblade populations in Ontario, all currently known populations comprise less than 50 stems. This is, however, not necessarily reflective of population number, as Purple Twayblade is a colonizing species that grows underground in association with its host fungus, and may not produce above ground stems every year.

2. Lack of regulatory protection for exploited wild populations

Not in any category. No known harvest in Ontario.

3. Direct threats

Special Concern. Threats to Purple Twayblade include housing development and urbanization, succession (shading by a maturing forest), inbreeding, browse by deer, the presence and continued spread of invasive species, and flooding caused by beaver dams (COSEWIC 2010; Mattrick 2004).

4. Specialized life history or habitat-use characteristics

Special Concern. Similar to many orchids, Liparis liliifolia has a very specific fungal associate. The fungus is the same over the entire range of this species and has virtually no genetic variation. The specificity of this association and the lack of the genetic variation within the fungus are surprising and not found among most orchids (Mattrick 2004; Whigham et al. 2006). Throughout its range, however, Liparis liliifolia occupies a variety of habitats, with new population discoveries giving a clear indication that this species is not as tied to Carolinan forest habitat as previously thought (COSEWIC 2010).

COSSARO criteria met (primary/secondary)

Endangered – [1/0]
Threatened – [2/0]
Special concern – [0/2]

Recommended Status: Threatened


Purple Twayblade (Liparis liliifolia) is Threatened in Ontario, downlisted from Endangered. This inconspicuous terrestrial perennial orchid occurs throughout the eastern and central United States. It occurs in a variety of habitats and colonizes successional habitats not typically visited by botanists. Purple Twayblades are increasing in abundance and distribution in the Midwest, but declining in New England. It occurs in scattered populations in southern and eastern Ontario and there is one recently discovered population in southern Quebec. The discovery of several new populations in recent years has extended its known range in Canada. The majority of the populations comprise few individuals, and the total known population size in Ontario remains small (< 300). Threats to Purple Twayblade include housing development and urbanization, succession, flooding caused by beaver dams, invasive species, small population sizes, and herbivory. Small, scattered populations in Ontario account for its conservation listing. Increased numbers of known populations as a result of enhanced survey effort account for the downlisting from Endangered.

Information sources

Brodribb, K.E. and M.J. Oldham. 2000. COSSARO Candidate V, T, E Species Evaluation Form for Purple Twayblade (Liparis liliifolia). Committee on the Status of Species at Risk in Ontario.

Brumback, W. E., L. J. Mehrhoff, R. W. Enser, S. C. Gawler, R. G. Popp, P. Somers, D. D. Sperduto, W. D. Countryman, and C. B. Hellquist. 1996. Flora Conservanda: New England. The New England Plant Conservation Program (NEPCoP) list of plants in need of conservation. Rhodora 98: 233-361.

COSEWIC. 2010. Update COSEWIC status report on Purple Twayblade (Liparis liliifolia) in Canada. Committee on the Status of Endangered Wildlife in Canada, 2-month Interim Status Report. Ottawa. xi + 24 pp.

Homoya, M.A. 1993. Orchids of Indiana. Indiana University Press, Indianapolis. 276 pp.

Mattrick, Christopher. 2004. Liparis liliifolia (L.) L.C. Rich. ex Lindley (Lily-leaved twayblade) Conservation and Research Plan for New England. New England Wild Flower Society, Framingham, Massachusetts, USA.

Natural Heritage Information Center (NHIC). 2010. Liparis liliifolia General Element Report in NHIC Elements Database. Accessed February, 2011.

NatureServe 2011. an Online Encyclopedia of Life. Accessed February 2011.

Sheviak, C.J. 1974. An introduction to the ecology of the Illinois Orchidaceae. Illinois State Museum, Scientific Papers XIV. Springfield, Illinois. 89 pp.

Whigham, D.F., J.P. O'Neilla, H.N. Rasmussen, B.A. Caldwell, & M.K. McCormick. 2006. Seed longevity in terrestrial orchids – Potential for persistent in situ seed banks Biological Conservation 129:24-30.

White, D.J. 2001. Update COSEWIC Status Report on the Purple Twayblade Liparis liliifolia in Canada, in COSEWIC assessment and update status report on the Purple Twayblade Liparis liliifolia in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. 1-10 pp.

Table 1: Northeastern North America rank, status and decline

Province/StateNorth America rank, status and decline
LBNot present
MBNot present
MENot present
NBNot present
NFNot present
NSNot present
PENot present

Occurs as a native species in 22 of 29 northeastern jurisdictions Srank or equivalent information available for 17 of 22 jurisdictions = 77% S1, S2, SH, or SX in 9 of 17 = 53%

Part 2: Ontario evaluation using COSEWIC criteria

Regional (Ontario) COSEWIC criteria assessment

Criterion A – Decline in total number of mature individuals

Insufficient information. Any declines that may be occurring may be being offset by increases elsewhere.

Criterion B – Small distribution range and decline or fluctuation

N/A. Although very small area of occupancy, this plant is not severely fragmented and locations likely >10 and no extreme fluctuations in population size.

Criterion C – Small and Declining Number of Mature Individuals

N/A. No declines are likely occurring.

Criterion D – Very Small or Restricted Total Population

TH. Meets Threatened D1 based on the total population being >250 and <1000 mature individuals.

Criterion E – Quantitative Analysis

N/A. None have been conducted.

Rescue effect

Possibly Orchid seeds are very mobile and this plant is not a habitat specialist. Its fungal associate is also widespread, although Purple Twayblade is not common in adjacent American states. The species appears to have been expanding its range in the Midwestern United States and its seeds are wind-dispersed, suggesting rescue is possible.