Xanthomendoza fulva

Family: Teloschistaceae

Bare-bottomed Sunburst (Xanthomendoza fulva) is a vivid yellow to orange foliose lichen commonly found on tree bark in Minnesota. It is distinguished by its narrow, often ascending lobes, granular soredia produced from the lower surface, and a white, nearly bare underside lacking true rhizines.

This page documents field observations used for identification. Visual presentation and artistic interpretation are handled separately in the Gallery section, Bare-bottomed Sunburst.

Description

Xanthomendoza fulva is recognized by:

Growth form: foliose
Thallus: yellow to orange-yellow, thin to moderately thick
Lobes: narrow (c. 0.2–0.6 mm), rounded to finely divided, often ascending at the margins
Surface features: mealy to granular soredia, primarily along the lower surface edges
Underside: white to pale, smooth
Attachment: loose to lightly attached, lacking true rhizines

Colonies are often irregular and variable, with transitions between granular and more distinctly lobed growth within a single thallus.

Substrate and Habitat

Typically found on:

Tree bark, especially hardwoods
Occasionally on wood; rarely on rock

Habitats include open woodlands, forest edges, and urban or suburban trees. The species often occurs in nutrient-enriched environments and tolerates human disturbance well.

Identification

Key features for field diagnosis:

Color: yellow to orange-yellow
Form: foliose, irregular rosettes
Surface: sorediate, especially along lower margins
Underside: white, nearly bare
Attachment: lacking rhizines
Reproductive structures: apothecia rare; pycnidia often present

This is the diagnostic core of the species.
Lower-surface soredia combined with a white, non-rhizinate underside are the most reliable characters.

Ecology and Notes

This species is highly variable in appearance and often co-occurs with other yellow foliose lichens, contributing to frequent misidentification. Moist or cold-season conditions tend to intensify coloration and make soredia more apparent.

Confirmed Minnesota observations are common and well represented by Research Grade records.

References

Consortium of North American Lichen Herbaria
Minnesota Lichen Guide
iNaturalist (Research Grade observations)