Chrysothrix xanthina (Vain.) Kalb

Description

Description: (From Harris & Ladd 2008) - Thallus crustose, leprose, thin, on bark, wood and rarely rock or bryophytes, bright yellow or greenish yellow, unstratified, of ± scattered granules usually coalescing into small discontinuous patches, sometimes into more extensive patches, when ± continuous one-few granules thick to ca. 100 µm, occasionally remaining as mostly separate granules; rhizohyphae absent; photobiont chlorococcoid, to 15 µm across. Granules spherical to ± irregular, 25-40 µm across; hyphae 2-4 µm across. Apothecia on a single Florida specimen (Buck 28935), arthonioid, yellow pruinose, ca. 0.1-0.2 mm across; spores 3-septate, ca. 10.5-12 x 2.5-3 µm (± immature?). Pycnidia not seen.

Illustrations: Color illustration: Harris and Ladd (2008; Opuscula Philolichenum, 5: 32, pl. 1, fig. 3).

Chemistry: (From Harris & Ladd 2008) - Chemistry: spot tests negative, UV–; pinastric acid.

Discussion: (From Harris & Ladd 2008) - Chrysothrix xanthina is distinctive in its relatively thin thallus, small granules, production of pinastric acid and occurrence on bark or wood. Rare specimens on rock are distinguished from C. onokoensis by thin thallus lacking rhizohyphae and from C. insulizans by more continuous thallus and producing pinastric acid instead of leprapinic? acid and calycin. Corticolous material assigned to C. insulizans is morphologically very similar and only separable with chromatography. Kalb (2001) resurrected C. xanthina from the synonymy of C. candelaris based on chemistry and soredial size (see above under C. candelaris). Kalb (2001) considered it a subtropical/tropical taxon and cited a single Florida specimen. However, material indistinguishable from his concept of C. xanthina is widely distributed in eastern North America from the Canadian border to Florida, and westward to the eastern edge of the mixed grass prairie regions of the Great Plains, occurring on both hardwoods and conifers. A variety of trees with both acidic and circumneutral to slightly basic bark are common substrates, including most of the common genera of trees in the region: Acer, Betula, Carpinus, Carya, Cercis, Crataegus, Fraxinus, Gleditsia, Gymnocladus, Juglans, Juniperus, Nyssa, Pinus, Platanus, Prunus, Quercus, Taxodium and Tilia. This species also occurs on decorticate hardwood and softwood, and rarely on lightly shaded, sheltered sandstone. The synonyms cited above were not included in Laundon (1981); both have apothecia. Since becoming aware of the critical characters in Chrysothrix, we have not re-examined the type material of Bilimbia stevensonii so that we have no record of soredial size or chemistry. Its definitive disposition is left for future study.

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