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Puzzling Rockcress - Sandbergia perplexa
State Rank Reason (see State Rank above)
Rare in Montana, where it is known only from the very southern end of the Bitterroot Valley on the Bitterroot National Forest. Spotted knapweed is known from at least one of the populations and further spread of invasive weeds at the known occurrences is likely without control measures. Trend data and repeat observations of the known occurrences are lacking.
Puzzling Rockcress is a rosette-forming, short-lived perennial with 1 to several erect stems that are 15-40 cm high and which arise from a simple or branched rootcrown. The lance-shaped basal leaves are 2-4 cm long and have petioles and deeply toothed to shallowly lobed margins. Upper stem leaves are smaller and sessile, and the foliage is covered with branched hairs. Stalked flowers occur at the stem tips in a compact, unbranched inflorescence that expands as the fruits mature. Each flower has 4 separate sepals, 4 separate, white petals that are 3-6 mm long, and 4 long and 2 short stamens. The style is ca. 1 mm long. The hairy, linear capsules, or siliques, are 1-2 cm long with a circular cross-section and are borne on erect to ascending stalks that are 10-17 mm long.
Flowering in May-June, fruiting in June.
Leaves of H. virgata clasp the stem, and the siliques are glabrous. Species of Arabis usually have flattened siliques.
Endemic to east-central ID and adjacent MT; one collection from southern Ravalli County and reported for Beaverhead County (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).
Observations in Montana Natural Heritage Program Database
Number of Observations:
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Sparsely vegetated, gravelly slopes of sagebrush steppe, mountain mahogany woodlands, or pine woodlands in the montane zone.
Ecological Systems Associated with this Species
Threats or Limiting Factors
STATE THREAT SCORE REASON
Reported threats to Montana's populations of Puzzling Rockcress include those that impact its habitat, limited to south Ravalli County (MTNHP Threat Assessment 2021). Noxious weeds and active logging are encountered at all populations. Widespread Spotted Knapweed (Centaurea stoebe) infestations negatively impact populations and rapidly spread following ground disturbance. Logging operations inflict such disturbance, favoring noxious weeds, and likely inflict direct damage to plants and populations. Information on the severity of direct impacts due to wood harvesting is needed to assess the relative contribution from this threat.
- Literature Cited AboveLegend: View Online Publication
- Lesica, P., M.T. Lavin, and P.F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
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