Allocetraria oakesiana (Tuck.) Randlane & Thell
Yellow ribbon lichen
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Allocetraria oakesiana, Cetraria oakesiana
Basis for Listing
Allocetraria oakesiana is found in the northeastern United States and has a typical Appalachian-Great Lakes distribution. It is very rare in Minnesota and has only been collected once in Cook County in a Picea mariana-Abies balsamea (black spruce-balsam fir) forest. It was never collected by Fink (1910), but may have been overlooked because it is often quite small and resembles a faded C. pinastri (powdered sunshine lichen). It is unlikely that A. oakesiana has recently invaded the area. This lichen is found near the ground on the bases of trees and on stumps and logs in cool, moist habitats. On Isle Royale, it is only found on the unburned parts of the island, which suggests that this species is intolerant of certain types of disturbance. When A. oakesiana was designated a state special concern species in 1984, too little information was available to assess its status with any certainty. However, recent survey efforts have failed to document any additional locations in Minnesota. For this reason, A. oakesiana was reclassified as state threatened in 1996.
Allocetraria oakesiana is a foliose (leaflike) lichen whose thallus (lichen body) is yellowish-green, 3-7 cm (1.2-2.8 in.) broad, with narrow (1-4 mm wide; 0.04-0.16 in.), more or less parallel lobes. The medulla (middle layer of the thallus) is white. The lower surface of the thallus is brown to light tan, with few rhizines (root-like structures). Apothecia (disk-like fruiting bodies) are rare. When present, apothecia can be up to 6 mm (0.24 in.) in diameter, with a brown disk and a thin margin (Thell et al. 1995). Pale yellow soredia (powdery vegetative propagules) are present on lobe tips and margins. When subjected to chemical spot tests, A. oakesiana does not respond to bleach (Wetmore 1981). Parmelia ulophyllodes (powder-edged speckled greenshield) is a somewhat similar lichen, but it has broader lobes and turns red when subjected to a bleach chemical spot test (Hale 1979).
In Minnesota, A. oakesiana was found in a shady, moist, undisturbed P. mariana-A. balsamea forest near Lake Superior. Elsewhere, this lichen usually occurs at the base of conifers, in moderately open conifer forests. It may be found in areas of high humidity, and typically occurs near water features such as lakes, streams, ponds, or pools. Allocetraria oakesiana may be found on the lower trunk of living or dead trees. It favors old-growth trees, and while not all collections are from old-growth forests, it has never been collected from very young stands. Absence of tall undergrowth is a habitat feature (U.S. Forest Service 1999).
Biology / Life History
Allocetraria oakesiana is sorediate. Soredia are asexual reproductive structures that include both the fungus and the algae. Soredia have a shorter dispersal range than spores. This species also reproduces sexually, with spore distribution by wind, rain, and insects.
Conservation / Management
Allocetraria oakesiana would benefit from maintenance of a continuous riparian buffer strip of uncut woods along streams. A 61 m (200 ft.) buffer of forest around a water source or bog that kept humidity at an acceptable level would satisfy the moisture requirements of this species (U.S. Forest Service 1999). Threats to this lichen include certain forms of timber harvest and environmental changes associated with global warming. Because Minnesota is near the edge of this lichen's natural range, climate change could result in loss of habitat and disruption of its precise environmental requirements. Potential threats from air pollution include mercury, sulfur dioxide, and nitrogen dioxide (U.S. Forest Service 1999).
Conservation Efforts in Minnesota
This species and other rare lichens are being targeted for botanical searches by scientists in an attempt to locate additional occurrences and conserve remaining populations.