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Clark, Jim & Steven L. Stephenson. Biosystematics of the myxomycetes Didymium squamulosum, Physarum compressum, and Physarum melleum: additional isolates. Mycotaxon 85: 85 - 89. 2003.

ABSTRACT: Twenty-four isolates of Didymium squamulosum, 18 isolates of Physarum compressum, and two isolates of Physarum melleum were cultured and their reproductive system determined.   These isolates are additions to the 85 isolates (33 D. squamulosum, 33 P. compressum, and 19 P. melleum) that have been studied previously.   Eleven of the 24  D. squamulosum isolates were nonheterothallic and presumptive apomictics, while the remaining 13 isolates belonged to three new biological species: A4 (three isolates from Costa Rica, sympatric with the A1 and A2 biological species), A5 (one isolate from Mexico), and A6 (one isolate from Thailand, two isolates from New Zealand, and six isolates from Australia).  Seventeen of the  P. compressum isolates were nonheterothallic, with the remaining isolate from Costa Rica (CR 18) being compatible with the previously determined A1 biological species isolated from the Canary Islands.   Both of the P. melleum isolates were nonheterothallic.   These results confirm and extend the conclusions derived from earlier studies.   The D. squamulosum morphospecies, which consists of two overlapping morphotypes, appears to be an extremely complicated species complex consisting of numerous geographically restricted sympatric and allopatric biological species and many apomictic lines.  The biological species are usually, but not always, confined to one of the morphotypes.  On the other hand, the P. compressum morphospecies seems to be a species complex consisting of a single uncommon but widespread biological species and countless apomictic lines with relatively minor morphological variations.   The Physarum melleum morphospecies is probably similar to P. compressum, although to date no heterothallic isolates have been reported.

KEY WORDS: apomixis, biological species, heterothallism

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