Swamp rose-mallow (Hibiscus moscheutos) COSEWIC assessment and status report: chapter 2

Executive Summary

Swamp Rose-mallow

Hibiscus moscheutos

Species Information

Hibiscus moscheutos is a robust perennial of the mallow family (Malvaceae) growing to two metres in height with up to eight showy blooms found in the axils of the upper leaves.  The large hollyhock-like flowers are unmistakable, with the pink or white petals 6-10 cm long.  The flowers are bisexual, and as is characteristic of all mallows, the stamens are united into a column arising from the centre of the flower.  The style protrudes from the tip of the staminal column and is tipped with five round stigmas.  When not in flower, the combination of tall stature, hairy, oblong or maple-like leaves, and nearly globular capsules is distinctive.

Distribution

The global range of H. moscheutos encompasses most of the eastern United States north of Florida and east of the Mississippi River, with a narrowing coastal distribution evident north of Maryland to Massachusetts.  The Canadian range is restricted to southern Ontario, where H. moscheutos is confined to the coastal marshes and remnant wetlands of Lakes Erie, St. Clair, and Ontario, with only two inland stations.  Hibiscus moscheutos appears to have expanded its range northeastward in Ontario over the last 15-20 years.

Habitat

In Canada, H. moscheutos is largely restricted to the Carolinian or Deciduous Forest Region.  However, recent discoveries in central and eastern Lake Ontario have extended the range of the species into the Great Lakes - St. Lawrence forest region.  All populations are confined to early successional wetlands that are associated with or have had a recent association with Lakes Erie, Ontario, or St. Clair.  The species is most common in deep-water Typha marshes, where it occurs along the interface with the open water in the cattail mat; and in meadow marshes.  It reaches its greatest numbers in dyked wetlands, where competition is controlled and the open habitat is maintained by periodic flooding.  The importance of water-level fluctuations in maintaining marsh habitat has been well documented in the literature.  Historically, populations of Hibiscus would have been maintained in early successional coastal habitats by natural fire, storms, and beaver activity.  Various forms of human disturbance also serve to maintain or create open conditions, well illustrated by several populations thriving in micro-wetlands along railway verges.  Rose-mallow is thus tolerant of both disturbance and unstable substrates.  With the low water levels of the Great Lakes over the past few years, water-level fluctuations that periodically expose and then re-flood, thus controlling Phragmites, shrubs, and small trees, are probably critical for the long-term suvival of this species in Canada.

Biology

Vegetative reproduction appears to be important in Hibiscus moscheutos, with clumps able to produce new flowering stems yearly.  Clumps may also become fragmented and dispersed by wind and wave action, facilitating the colonization of new sites.  In areas to the south of Ontario, most pollination is accomplished by a single species of non-social bee, Ptilothrix bombiformis, with much of the bee's activity centred around these plants.  Other visitors to flowers noted are several species of moths, butterflies, small bees and flies, but none appear to be effective pollinators.  It is important to note that P. bombiformis has not been reported to occur in Canada.  Hibiscus moscheutos is found in open wetlands and is probably dependent upon periodic burning, flooding, drought, or anthropogenic disturbance to decrease shading from trees and shrubs and create open habitat.

Population Sizes and Trends

There are 51 extant stations for Hibiscus moscheutos in Canada, compared with 40 documented for the original status report.  Hibiscus moscheutos varied from an infrequent component of a community, with only a few flowering stems, to the dominant species, with an estimated 10,000 flowering stems present representing an unknown number of individual plants.  The total number of stems in Canada is estimated at ~25,000.  Twenty populations are believed to be extirpated, based on supplementary information of field surveys conducted late in 2003.

Although many stations have been known for over 50 years, it is difficult to determine whether populations have been declining or fluctuating in numbers over this time period.  This is largely due to the fact that prior to 1985, quantitative data was gathered at only three stations.  In the 17 years since the 1985 field surveys and those of the update report in 2002, the number of populations seem to have remained relatively stable.  Seven of the populations and four subpopulations documented in the original report are now believed extirpated, however all but two of these are small populations.  Based on his field observation in 2002, the senior author believes that some of the stations are in decline as a result of competition with Phragmites, and to a lesser extent Typha X glauca.

Limiting Factors and Threats

Habitat quality appears to be declining at a majority of Hibiscus stations as a result of continuing nutrient loading, successional change, and general lack of natural disturbance.  The resulting proliferation of the exotic grass Phragmites and the hybrid cattail, Typha X glauca, is a symptom of this degradation, as these species exploit the compromised environment.  It is believed that Phragmites has probably resulted in the extirpation of populations or subpopulations of Hibiscus from six sites.  Phragmites monocultures can replace diverse wetland vegetation and decrease plant diversity by causing alterations in nutrient cycling and hydrologic regimes.  The second-most problematic invasive species impacting Hibiscus is hybrid cattail.  It is dominant or co-dominant (invariably with Phragmites) at a number of the Hibiscus sites, and at one is believed to be effectively out-competing the Hibiscus over the last few years. 

Existing Protection

The species is recognized as Critically Imperiled (S1) in Wisconsin, Imperiled (S2) in Rhode Island and Vulnerable (S3) in Michigan; it is not at risk in 24 other US states.  It is considered as secure globally (G5) and has been accorded a national rank in Canada of Vulnerable (N3). 

The major coastal marshes that support Hibiscus are quite secure, either as protected parks, private hunt clubs, or First Nation Lands that are leased out for waterfowl hunting.  There is thus little chance that these marshes will be converted to other uses, and none of the major marshes have been developed since the original status report.  Many are also identified as provincially significant wetlands, and are thus protected under the Provincial Policy Statement.

COSEWIC History

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal–Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list. On June 5, 2003, the Species at Risk Act (SARA) was proclaimed. SARA establishes COSEWIC as an advisory body ensuring that species will continue to be assessed under a rigorous and independent scientific process.

COSEWIC Mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses the national status of wild species, subspecies, varieties, or other designatable units that are considered to be at risk in Canada. Designations are made on native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fishes, arthropods, molluscs, vascular plants, mosses, and lichens.

COSEWIC Membership

COSEWIC comprises members from each provincial and territorial government wildlife agency, four federal entities (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biodiversity Information Partnership, chaired by the Canadian Museum of Nature), three non–government science members and the co–chairs of the species specialist subcommittees and the Aboriginal Traditional Knowledge subcommittee. The Committee meets to consider status reports on candidate species.

Definitions (November 2004)

Species
Any indigenous species, subspecies, variety, or geographically defined population of wild fauna and flora.

Extinct (X)
A species that no longer exists.

Extirpated (XT)
A species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)
A species facing imminent extirpation or extinction.

Threatened (T)
A species likely to become endangered if limiting factors are not reversed.

Special Concern (SC)*
A species of special concern because of characteristics that make it particularly sensitive to human activities or natural events.

Not at Risk (NAR)*
A species that has been evaluated and found to be not at risk.

Data Deficient (DD)***
A species for which there is insufficient scientific information to support status designation.

* Formerly described as “Vulnerable” from 1990 to 1999, or “Rare” prior to 1990.

** Formerly described as “Not In Any Category”, or “No Designation Required.”

*** Formerly described as “Indeterminate” from 1994 to 1999 or “ISIBD” (insufficient scientific information on which to base a designation) prior to 1994.

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list.

The Canadian Wildlife Service, Environment Canada, provides full administrative and financial support to the COSEWIC Secretariat.

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