Overview

Distribution

National Distribution

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

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Global Range: Past reports listing this species as possibly occurring in Kentucky or Georgia are erroneous. For more information as to the explanation and history of the false reports see Patrick and Wofford (1980).

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Physical Description

Morphology

Description

Plants caulescent, 65–200 cm; fibrous rooted. Stems terete, glabrous. Leaves: basal caducous; cauline opposite, petiolate; blades lanceolate, hastate, ovate, or sagittate, 1–24 × 0.5–18 cm, bases cuneate, or round (distal), or cordate, truncate, hastate, or sagittate (proximal), margins coarsely dentate or entire, apices acuminate to acute, faces sparsely hirsute, hispid, or scabrous. Phyllaries 11–15 in 2–3 series, outer reflexed or appressed, apices acute, abaxial faces scabrous. Ray florets 7–9; corollas yellow. Disc florets 20–40; corollas yellow. Cypselae 7–8 × 5–6 mm; pappi 0.5–1 mm. 2n = 14.
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Diagnostic Description

Flowering heads are smaller than many other Silphium. Leaves regularly occurring along the stem (Cronquist 1980), but [p]erhaps the most important giveaway field character. . .is the shape of the base of the lowermost pair of leaves. Such leaves have hastate-subhastate bases or, in other words, outwardly flared or lobed bases, each attached by a copiously hairy, long, more or less declined petiole (Patrick and Wofford 1980).

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Ecology

Habitat

Comments: Silphium brachiatum is only known from the Cumberland Plateau (sometimes referred to as the Appalachian Plateau in Alabama) in Tennessee and Alabama and the Tennessee Valley of Alabama. The species is found on Bangor and Monteagle Limestone formations (Schotz 1998), within open dry mixed forests of various oaks and hickories including Quercus muehlenbergii, Carya glabra, and Juniperus virginiana. The species has been found on roadsides, powerline right-of-ways, and in forests with substantial past disturbance. Specifically, the habitat requirements include calcareous soils with exposed limestone bedrock, dry sites with partial shade and with forest openings (Patrick and Wofford 1980).

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Population Biology

Number of Occurrences

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 21 - 80

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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Silphium brachiatum

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 2
Species With Barcodes: 1
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Conservation

Conservation Status

National NatureServe Conservation Status

United States

Rounded National Status Rank: N2 - Imperiled

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NatureServe Conservation Status

Rounded Global Status Rank: G2 - Imperiled

Reasons: Silphium brachiatum has a narrow range in southern Middle Tennessee and northern Alabama. Currently there are only 39 extant occurrences, 30 of which are ranked as viable. Although limited in distribution, the habitat in which the species occurs does not seem rare. Nine Alabama occurrences are found on protected lands (Schotz 1998) and three occurrences in Tennessee are within designated state natural areas.

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Global Short Term Trend: Relatively stable to decline of 30%

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Threats

Comments: As the species occurs in cleared or open areas, selective timber cutting likely wouldn't adversely impact Silphium brachiatum and may benefit the species by providing additional light. However, intensive forestry practices including clearcutting and site preparation would pose a threat (Schotz 1998). Since many of the occurrences are along road and powerline right-of-ways, maintenance or enlargement could impact the species (but mechanical clearing of woody plants may aid the species). The species' association with limestone could prove problematic. As of 2006, there are plans for at least one limestone mine to be reactivated which would impact a Tennessee occurrence (Withers, pers. comm.). Threats from limestone quarrying were also noted by Patrick and Wofford (1980). One Alabama occurrence with 75 - 100 plants is under threat from residential development. In his 1998 status survey, Schotz did not observe impacts from mammal browsing or insects. In studying the lack of flowering plants in a Tennessee State Natural Area, Lincicome (2005) concluded that deer browsing did not cause apical meristem damage, but he did hypothesize that the observed damage was the result of aphids. Various occurrences are ranked as viable and Silphium brachiatum still occurs at the type locality found in 1867. However, it is unclear what effect development may have on the species.

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Relevance to Humans and Ecosystems

Risks

Stewardship Overview: Silphium brachiatum appears to do better outside of heavy shade. Hand thinning of timber at sites with heavy forest cover is recommended. Some of the occurrences along roadways may be mowed, but care should be taken for such disturbance and increased light levels may promote the growth of more weedy species (Schotz 1998). Fire does not appear to either benefit or adversely impact the species (Kral 1983).

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