Which Irish botanist first identified Fleming's mould specimen as Penicillium rubrum?

The Irish botanist who first identified Fleming’s mould specimen as Penicillium rubrum was C. J. La Touche.

Charles John Patrick La Touche was working at St Mary’s Hospital in London as a mycologist when Fleming’s contaminated bacterial culture attracted attention in 1928. Fleming recognized that the mould inhibited bacterial growth, but identification required specialist knowledge of fungi. La Touche examined the specimen and identified it as P. rubrum, the name used in Fleming’s original publication.

The classification did not remain settled. In 1931, American mycologist Charles Thom re-examined the specimen and associated it with P. notatum and the P. chrysogenum group. Modern genomic work later showed that Fleming’s strain belongs to P. rubens, so P. rubrum is now a historical identification rather than the accepted current name.

Joseph Bigger influenced Fleming’s bacteriological work, while Ronald Hare later investigated the discovery’s circumstances. Charles Thom revised the fungal classification, but La Touche made the first identification asked about here.