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COSEWIC assessment and update status report on the Bluehearts in Canada

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COSEWIC
Executive Summary

Bluehearts
Buchnera americana

Species Information

Bluehearts is a perennial ranging in height from 40 to 80 cm; plants are usually unbranched, have hairy stems and sessile, opposite leaves. A flowering spike of deep purple, stalkless flowers is produced at the top of the plant. In Ontario, flowering begins in mid-July and lasts until early September. Fruits are oblong capsules about 7 mm long. The species is hemiparasitic on a variety of deciduous and coniferous trees, being linked to the root system of these by way of haustorial attachments.

Distribution

Buchnera americana is extant in 11 states from Ohio and Indiana to Georgia and Missouri. The areas of greatest concentration are in Tennessee, Kentucky, Arkansas and Missouri. It occurs as a northern disjunct along a 10 km stretch of Lake Huron in southwestern Ontario.

Habitat

Plants tend to occur along the edges of wet, interdunal depressions in Ontario.

Biology

The species is hemiparasitic on the roots of a great variety of trees including white pine, red ash, eastern cottonwood, white oak and presumably other plants but can mature without parasitic attachment. It has been described as a perennial plant, however there is some question whether it may survive primarily as an annual in Ontario and possibly other northern states. The small seeds of bluehearts require light for germination and can remain viable in the soil for 2.5-3 years based on limited testing. Bluehearts may be butterfly pollinated, but self-pollination, based on colour and morphology, may be widespread.

Population Sizes and Trends

Bluehearts undergoes highly variable population fluctuations from year to year. The total number of plants in 1981 was 2182, which was the only year when all 8 known sites were surveyed. Significant decreases occurred during years of high water levels such as in 1986 and in 1997 when fewer than 600 plants were counted at 6 extant sites. In 1988, there was a lengthy drought during the summer that may have also reduced numbers of flowering plants. 

Limiting Factors and Threats

Major natural limiting factors include the very specific habitat requirements and the dynamic nature of habitat. This is a seral species that disappears from stable communities. In Ontario, fluctuating water level is an extremely important factor in maintaining the open conditions favoured by this species. The major anthropogenic impact in Ontario is a drastic reduction in amount of natural interdunal habitat due to conversion for cottages and residences. This species is increasingly threatened by recreational activities. High water levels reduce the numbers of plants present in a given year but contribute to maintaining open habitat required by this species.

Special Significance of the Species

Bluehearts is of particular interest and significance because of its facultative parasitic life style, its considerable disjunction from the core populations in the USA, and its specificity to a narrow habitat range in Ontario where it relies on water level fluctuations to maintain its open habitat.