Gulliver, our logopillar
 M o n a r c h W a t c h Nav Links
Reading Room
READING
ROOM

Introduction

Articles

Season
Summaries


Scientific
Bibliography


Classroom
Bibliography


Frequently
Asked
Questions


monarch

Home
Help
Search
Order

Site by
JpL
Updated
01-FEB-99

Articles : The Milkweeds of Canada (Asclepias spp.)

Status, Distribution, and Potential Impact from Noxious Weed Legislation

Asclepias speciosa Torr. - Showy Milkweed

Description

This robust Milkweed grows to 1.5 meters tall and has opposite leaves that are oblong and blunt at each end. The flower clusters are few but large and terminal or in the uppermost leaf axils. The hoods of each large, greenish-purple flower hide the short, incurved horns. The pods are densely hairy.

Illustration

An illustration can be found in Gleason (1968) vol 3, page 78.

Biological and Economic Significance

This Milkweed is an uncommon plant whose natural significance is largely unknown. The species is considered the primary food source of the larvae of Monarch Butterfly (Danaus plexippus) in western Canada (Crolla & Lafontaine, 1996).

Distribution

Asclepias speciosa has a moderate range in west-central United States from Washington to Minnesota and south to Oklahoma and California. In Canada it occurs in southern British Columbia, southern Alberta, southern Saskatchewan, and southern Manitoba.

Figure: North American distribution of Asclepias speciosa

General Habitat

Thickets, roadsides, and moist grassland.

Population Biology

The average population size for this Milkweed is unknown.

Evidence of Threats to Survival

No imminent threats are known. Due to its grassland and roadside habitat, it could be targeted by "weed control" programs especially since it bears a superficial resemblance to Common Milkweed (Asclepias syriaca). It is listed as a noxious weed in Manitoba and is sometimes targeted for control.

Present Legal or Other Formal Status

This Milkweed has no legal protection, nor is it considered rare in any Canadian province. Its status in the United States is unknown.

Assessment of Status

Asclepias speciosa is uncommon from British Columbia to southern Manitoba.


Asclepias sullivantii Engelm. ex Gray - Sullivant's Milkweed

Description

This Milkweed grows to 1.5 metres tall and has oval-shaped leaves that are broadest in the middle and taper abruptly at both ends. This plant is quite similar to Common Milkweed (Asclepias syriaca) except that this species is entirely smooth and the leaf ends are very blunt. The flower clusters are compact and many-flowered and are terminal or sometimes one or more clusters occur also in the uppermost leaf axils. The hoods of each flower hide the slightly incurved horns. The flowers are white, pink, or lavender.

Illustration

An illustration can be found in Gleason (1968) vol 3, page 79.

Biological and Economic Significance

This Milkweed is a very rare plant whose natural significance is largely unknown. The species could be used occasionally as a food source by the larvae of Monarch Butterfly (Danaus plexippus), however, due to its very limited range and extreme rarity, it is probably not a significant food source. The plant has a high rubber content and was a candidate for possible latex production during the Second World War (Fox, 1944).

Distribution

Asclepias sullivantii has a moderate range in east-central United States from Ohio to Minnesota and south to Oklahoma. In Canada it occurs only in extreme southern Ontario.

Figure: North American distribution of Asclepias sullivantii

Figure: Ontario distribution of Asclepias sullivantii

General Habitat

Wet meadows, moist prairies, railway embankments, and roadsides.

Population Biology

Fox (1944) reported that several colonies investigated on Walpole Island in extreme southwestern Ontario were "not large" in size. Notes on the DAQ herbarium specimens collected by M. J. Oldham report colonies of 10 plants and 20 plants.

Evidence of Threats to Survival

No imminent threats are known. Since it has been recorded in Ontario along roadsides and railway embankments, it could be targeted by "weed control" programs especially since its bears a superficial resemblance to Common Milkweed (Asclepias syriaca).

Present Legal or Other Formal Status

This Milkweed has no legal protection, however, it is considered rare in Ontario in Argus & Keddy (1984). It is considered rare in Canada and is given the priority ranking of "3" in Argus & Pryer (1990) because of its absence or rarity in bordering states and because it is considered to be "N2" nationally and "S2" in Ontario where "2" indicates "imperiled because of rarity". It is regarded as "S2" in Ontario (very rare) in Olham (1994).

In the United States, it is regarded as a "G5" species (Argus & Pryer, 1990) which means that it is "abundant and demonstrably secure with many occurrences".

The status in individual states from Argus & Pryer (1990) is as follows: "SH" (Historical-not-recorded since 1900) - North Dakota; "S1" (Critically imperiled) - Michigan; "S1S2" (Critically imperiled or imperiled) - Wisconsin "S4" (Apparently secure) - Iowa; and status uncertain or unknown - Arkansas and South Dakota.

Assessment of Status

Asclepias sullivantii is very rare in extreme southern Ontario--its only Canadian occurrence. A 1991 collection made by M. J. Oldham (specimen at CAN) and 1987 and 1990 collections, also made by M. J. Oldham (specimens at DAO), are shown on the Ontario map. The new records occur within the known range of the species and do not change its rare status.


Asclepias syriacaL. - Common Milkweed

Description

This Milkweed grows to 1.5 metres tall and has oval-shaped leaves that are broadest in the middle and taper abruptly at both ends. This plant is more -or-less hairy throughout. The flower clusters are compact and many-flowered and are terminal and in the uppermost leaf axils. The hoods of each flower are quite spreading and don't hid the short incurved horns. The flowers are normally greenish-purple but white-flowered forms do occur (Dore, 1944). The pods are quite distinctive because of their densely hairy and "warty" appearance on stalks that are bent downward.

Illustration

An illustration can be found in Gleason (1968) vol 3, page 77.

Biological and Economic Significance

This Milkweed is a very common plant in eastern North American whose natural significance is largely unknown. During the late stages of the Second World War, the leaves of Common Milkweed were gathered in Ontario for their possible use as a source for "rubber" and the mature pods were gathered for possible use as a replacement for kapok in life jackets (Groh & Dore, 1945). It is not known how useful these products were but there is no evidence that their collection and use developed beyond the "pilot project" stage. The species is the most abundant and widespread of the Canadian Milkweeds and is the main food source for the larvae of Monarch Butterfly (Danaus plexippus) in Canada (Malcolm et al., 1989; Urquhart & Urquhart, 1979).

Distribution

Asclepias syriaca has a moderate range in east-central United States from Maine to North Dakota and south to Kansas and Georgia. In Canada it occurs in Nova Scotia to southeastern Saskatchewan. Malcolm et al., (1989) report that the present range of this species is essentially the same as that shown in Woodson (1954), however, it is now more common in many areas where it was of sporadic occurrence. As in 1945, its main centre of abundance in Canada is in southern Ontario in the Sarnia, Hamilton, Toronto, Kingston, and Belleville areas (Dore & Groh, 1945; Urquhart & Urquhart, 1979). Since the 1945 surveys, the species has also become very common in portions of central and northern Ontario, especially in the vicinities of Sudbury, Sault Ste. Marie, and Thunder Bay (Urquhart & Urquhart, 1979).

Figure: North American distribution of Asclepias syriaca

Figure: Saskatchewan distribution of Asclepias syriaca

General Habitat

Fields, meadows, agricultural land, prairies, railway embankments, and roadsides.

Population Biology

Surveys were conducted for Common Milkweed in Ontario and Quebec in the mid 1940's (Groh & Dore, 1945). In these surveys, stands varied from a few isolated plants to patches of tens of thousands of stalks. In Michigan, Wilbur (1976) reports colonies of up to several thousand stems. Malcolm et al., (1989) studies Common Milkweed across its North American range and reported patch sizes from four to 25,000 stems with an average of 345 stems. This species spreads vegetatively by means of underground rhizomes that may form large clones of up to several thousand stems (Gleason, 1968). Normally, each patch represents a single clone (Wilbur, 1976). Even though other species of Milkweed are able to reproduce vegetatively, this species is the most prolific (Wilbur, 1976). Although the most important means of reproduction in this species is by vegetative means (Wilbur, 1976), Common Milkweed is able to produce large numbers of seeds compared to other Milkweed species. These air-borne propagules enable long-distance spread.

Evidence of Threats to Survival

It is considered to be a noxious weed in Nova Scotia, Manitoba, Quebec, and Saskachewan. All Milkweeds are considered noxious weeds in Ontario, however, this is the primary species of concern. In provinces--such as Nova Scotia--where there is a limited population, the species could be eliminated by an aggressive control program. No imminent threats are known in Ontario and Quebec because the species is so abundant.

Present Legal or Other Formal Status

This Milkweed has no legal protection and it is considered common or uncommon across most of its Canadian range, except is Saskatchewan where it is considered to be rare (Maher et al., 1979). Its status in the United States is unknown.

Assessment of Status

Asclepias syriaca is very common in southern Ontario--although less common elsewhere, it also occurs from Saskatchewan--where it is rare--to Nova Scotia.


Asclepias tuberosaL. - Butterfly-weed

Description

This distinctive Milkweed grows to 70 centimetres tall and has alternate to opposite, thick, fleshy leaves that are linear to lance-shaped. The entire plant is hairy and is often much-branched. It is the only Milkweed that does not have milky juice. The flower clusters are several-flowered and are terminal and also in many of the uppermost leaf axils. The hoods of each flower barely conceal the straight horns. The flowers are a distinctive yellow-orange colour and the seed pods are slender.

Illustration

An illustration can be found in Gleason (1968) vol 3, page 75.

Biological and Economic Significance

This Milkweed is an uncommon plant whose natural significance is largely unknown. The species could be used occasionally as a food source by the larvae of the Monarch Butterfly (Danaus plexippus), however, due to its limited range, it is probably not a significant food source.

Distribution

Asclepias tuberosa has a wide range in the United States from New England to North Dakota and south to Florida and Arizona. In Canada it occurs only in extreme southwestern Quebec and in Southern Ontario.

Figure: North American distribution of Asclepias tuberosa

General Habitat

Dry sandy soil of meadows, open woods, and prairies.

Population Biology

In Michigan, Wilbur (1976) reports that it occurs in colonies that range from isolated individuals to patches containing several hundred plants. This species is slow to reach flowering size (Woodson, 1954) but individual plants can be quite long-lived-one individual reported in Wilbur (1976) is known to be over 25 years old. Butterfly-weed is rarely affected by herbivores but only about 1% of flowers produce mature pods (Wilber, 1976).

Evidence of Threats to Survival

No imminent threats are known. Due to its lack of abundance and its "unmilkweed-like" appearance, it is not likely to be targeted by "weed control" programs.

Present Legal or Other Formal Status

This Milkweed has no legal protection, however, it is considered rare in Quebec in Bouchard et.al., (1983). The Quebec record may not be native (Bouchard et.al., 1983). Its status in the United States is unknown.

Assessment of Status

Asclepias tuberosa is very rare in extreme southwestern Quebec and uncommon in southern Ontario-its only Canadian occurrences.


Asclepias variegataL. - Variegated Milkweed

Description

This Milkweed grows to one metre tall and has oval-shaped, opposite leaves that are broadest in the middle and generally taper abruptly at both ends. The flower clusters are compact and many-flowered and are terminal or sometimes one or more clusters occur also in the uppermost leaf axils. The hoods of each flower hide the short, flat horns. The flowers are white with a purplish centre.

Illustration

An illustration can be found in Gleason (1968) vol 3, page 78.

Biological and Economic Significance

This Milkweed is a very rare plant whose natural significance is largely unknown. The species could be used occasionally as a food source by the larvae of Monarch Butterfly (Danaus plexippus) if it still occurred in Ontario, however, it is probably not a significant food source.

Distribution

Asclepias variegata has a moderate range in the southeastern United States from New England to Ohio and south to Florida and Texas. In Canada it is known only from an 1859 record in southern Ontario. Since this is a showy species that hasn't been recorded in the country in over 130 years, the record may be based on a cultivated plant or a short-lived escape from cultivation (Argus & Keddy, 1984; Morton & Venn, 1990). Cultivated or not, this Milkweed appears to be extirpated in Canada.

Figure: North American distribution of Asclepias variegata

Figure: Ontario distribution of Asclepias variegata

General Habitat

Upland woods and thickets.

Population Biology

The average population size for Variegated Milkweed is impossible to judge because the species' occurrence in Canada is based on a single, very old record.

Evidence of Threats to Survival

This Milkweed appears to be extirpated in Canada.

Present Legal or Other Formal Status

This Milkweed has no legal protection, however, it is considered rare in Ontario in Argus & Keddy (1984). It is considered rare in Canada and is given the priority ranking of "3" in Argus & Pryer (1990) because of its absence or rarity in bordering states and because it is considered to be "NIX" nationally and "SX" in Ontario where "X" indicates "apparently extinct or extirpated without exception that it will be rediscovered". It is regarded as "SE?" in Ontario (possibly not native) in Oldham (1994).

In the United States, it is regarded as a "G5" species (Argus & Pryer, 1990) which means that it is "abundant and demonstrably secure with many occurrences".

The status in individual states from Argus & Pryer (1990) is as follows. "S1" (Critically imperiled)-Connecticut, New York, and Ohio, "S2" (Imperiled)-Indiana and New Jersey.

Assessment of Status

This Milkweed appears to be extirpated in Canada. It is not clear whether the only known record (made in 1859) is from garden material, from a garden escape, or from a naturally occurring stand that no longer exists.


Asclepias verticillataL. - Whorled Milkweed

Description

This slender, distinctive Milkweed grows to 50 centimetres tall and has numerous linear leaves that are arranged on the stem in whorls of three to six. The several flower clusters are terminal and in the upper leaf axils. The hoods of each greenish-white flower are surpassed by the curved horns.

Illustration

An illustration can be found Gleason (1968) vol 3, page 75.

Biological and Economic Significance

This Milkweed is a relatively rare plant whose natural significance is largely unknown. The species could be used occasionally as a food source by the larvae of Monarch Butterfly (Danaus plexippus), however, due to somewhat limited range and rarity, it is probably no a significant food source.

Distribution

Asclepias verticillata has a moderate range in the east-central United States from New England and Florida across to North Dakota and Texas. In Canada it occurs in southeastern Saskatchewan, southern Manitoba, and southwestern Ontario.

Figure: North American distribution ofAsclepias verticillata

Figure: Ontario distribution of Asclepias verticllata

Figure: Saskatchewan distribution of Asclepias verticllata

General Habitat

Dry fields, roadsides, and open sandy woods.

Population Biology

In southwestern Ontario, Oldham et al. (199l) report it to be very rare and localized, but with weedy tenancies. Wilbur (1976) described colonies in Michigan as dense but widely scattered, however, he did not report actual plant numbers.

The species can reproduce vegatatively under certain circumstances (Kephart, 1981) resulting in colonies several metres across that consist of just a few genetic individuals (Wilson et al., 1979). Whorled Milkweed is largely self-incompatible but some seeds may be produced by self-pollination (Wilson et al., 1979). Plants tend to be long-lived and are not affected much by herbivores (Wilbur, 1976).

Evidence of Threats to Survival

No imminent threats are known. Due to its roadside and field habitat, it could be targeted by "weed control" programs.

Present Legal or Other Formal Status

This Milkweed has no legal protection, however, it is considered rare in Saskatchewan in Maher et al., (1979), rare in Ontario in Argus & Keddy (1984), and uncommon in Manitoba. Since it is not rare in all of its Canadian range, it has no priority ranking in Argus & Pryer (1990). Its status in the United States is unknown.

Assessment of Status

Asclepias verticillata is rare in southwestern Ontario and in southeastern Saskatchewan. It is uncommon in Manitoba. A 1992 collection made by M.J. Oldham (specimen at CAN) is shown on the Ontario map. The new record occurs within the known range of the species and does not change its rare status in Ontario.


Asclepias viridifloraRaf. - Green Milkweed
(Acerates viridiflora(Raf.) Pursh ex Eat.)

Description

This Milkweed grows to 80 centimetres tall and has broad, opposite leaves that are blunt at both ends. The lateral flower clusters are densely-flowered in the upper leaf axils. The hoods of the greenish-white flowers lack horns.

Illustration

An illustration can be found in Gleason (1968) vol 3, page 80.

Biological and Economic Significance

This Milkweed is a relatively rare plant whose natural significance is largely unknown. The species could be used occasionally as a food source by the larvae of Monarch Butterfly (Danaus plexippus), however, due to somewhat limited range and rarity, it is probably not a significant food source.

Distribution

Asclepias viridiflora has an extensive range in the east-central United States from southern New England and Georgia across to Wyoming and New Mexico. In Canada it occurs in southern British Columbia, southeastern Alberta, southern Saskatchewan, southern Manitoba, and southern Ontario.

Figure: North American distribution of Asclepias viridiflora

Figure: Ontario distribution of Asclepias viridiflora

General Habitat

Sand dunes, dry prairie hillsides, and open sandy woods.

Population Biology

The average population size for this Milkweed is unknown. Green Milkweed suffers from herbivore damage but it has a low mortality due to its large root storage capacity (Wilbur, 1976).

Evidence of Threats to Survival

No imminent threats are known. Due to its habitat in woods and dunes, it is not likely to be targeted by "weed control" programs.

Present Legal or other Formal Status

This Milkweed has no legal protection, however, it is considered rare in Alberta in Argus &White (1978), rare in Ontario in Argus & Keddy (1984), and uncommon in Manitoba. Since it is not rare in all of its Canadian range, it has no priority ranking in Argus & Pryer (1990). Its status in the United States is unknown.

Assessment of Status

Asclepias viridiflora is rare in southern Ontario and in southeastern Alberta. It is uncommon in Manitoba.

Table of Contents Next Page

w w w . M o n a r c h W a t c h . o r g
m o n a r c h @ k u . e d u

spacerAll material on this site © Monarch Watch unless otherwise noted. Terms of use.
Monarch Watch (888) TAGGING - or - (785) 864-4441
monarch@ku.edu