Hot Spring Phacelia - Phacelia thermalis
State Rank Reason
Hot spring phacelia is known from a very small number of sites in northeastern Montana, where it is disjunct from its primary range (northern California to southwestern Idaho). The species is an annual and may be vulnerable to competition from invasive exotics, particularly sweet clover, which is widespread in the type of habitat where hot spring phacelia has been found.
General Description
Hot Spring Phacelia is an annual that is branched from the base. It has prostrate or ascending stems. The alternate leaves have broadly lance-shaped blades that are 1-9 cm long with toothed and deeply lobed margins and well-developed petioles. Foliage is glandular-hairy. The short-stalked flowers are borne in crowded, narrow, 1-sided, curved spikes that are up to 10 cm long. The spikes unwind as they mature and originate in the leaf axils. The lavendar to whitish flowers each have a 5-lobed tubular corolla that is 3-4 mm long and 5 narrowly lance-shaped, hairy sepals that are as long as the corolla in flower but twice as long in fruit. The stamens are included in the corolla tube. The fruit is a capsule with 2-4 seeds.
Phenology
In Montana, collection dates range from June 12 to July 9, the latter presumed to be in fruit.
Diagnostic Characteristics
The similar P. ivesiana has linear calyx lobes, transversely corrugated seeds and is known only from Carbon County. P. scopulina has leaves that are lobed less than halfway to the midrib, and is known only from southern Silver Bow County. In central and eastern Montana, the only other annual Phacelia with pinnately lobed or divided leaves is Phacelia linearis, which is single-stemmed with linear leaves and showy petals that exceed the calyx. Hot spring phacelia also bears superficial resemblance to annual species in other genera of the Waterleaf Family, but has a multi-flowered inflorescence as opposed to solitary flowers.
General Distribution
Summary of Observations Submitted for Montana
Number of Occurrences: 5
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Relative Density
Recency
(Records associated with a range of dates are excluded from time charts)
Distribution Comments
This species is native from northern California to southeastern Oregon and east to southwestern Idaho and Montana (Hickman 1993). It has been reported introduced in Saskatchewan (Scoggan 1978).
Habitat
Habitat information for the very few Montana records of this plant varies widely. In Fergus County it was collected on level ground immediately above a steep-sloped coulee. The Garfield County collection came from a steep slope immediately above the beach of York Island (Heidel 1994). It occupies open to partially wooded settings; the only associated species mentioned in collection records is Douglas-fir at the Fergus County site.
Ecology
Hot spring phacelia is an annual and population numbers may fluctuate significantly from year to year. It occurs in disturbed habitats, and Scoggan (1979) reports it as introduced in Saskatchewan.
Management
As an annual species near the northern limit of its range, this plant may be particularly vulnerable to competition from weeds. Its habitat in northeastern Montana has been extensively invaded by sweet clover (Melilotus spp.), which can invade arid microhabitats, shifting the course of succession and out-competing native plant species (Heidel 1994).
References
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Heidel, B. L. 1994. Sensitive plant species survey in Garfield and McCone Counties, Montana. Unpublished report to the Bureau of Land Management. Montana Natural Heritage Program, Helena, Montana. 58 pp. plus appendices.- Scoggan, H. J. 1979. The flora of Canada. Part 4: DICOTYLEDONEAE (LOASACEAE to COMPOSITAE). National Museum of Natural Sciences Publications in Botany No. 7(4). Ottawa, Canada. 1711 pp.
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