Fusarium clavum represents phylo-species FIESC 5 (O’Donnell et al. 2009) resolved as a well-supported clade (ML-BS = 94 %, MP-BS = 82 %, PP = 1.0) in the Equiseti clade, closely related to F. compactum, F. duofalcatisporum, F. ipomoeae and F. lacertarum. All five of these species produce only falcate aerial conidia (Gerlach & Nirenberg 1982, Subrahmanyam 1983, Leslie & Summerbell 2006, Wang et al. 2019), a feature apparently unique to this phylogenetic group. Fusarium clavum forms abundant lateral phialidic pegs on the aerial mycelia, a characteristic shared with F. duofalcatisporum, but not known for F. compactum, F. ipomoeae and F. lacertarum (Gerlach & Nirenberg 1982, Subrahmanyam 1983, Leslie & Summerbell 2006, Wang et al. 2019). However, the falcate aerial conidia of F. clavum (1– 2(– 3)-septate; 13 – 30 × 3 – 4 μm overall) are smaller than those of F. duofalcatisporum (1– 3(– 4)-septate; 13 – 40 × 2 – 5 μm overall). Isolates of F. clavum included in this study were obtained from environmental, plant and human samples collected in Africa, Asia, Europe and North America, indicative of a broad distribution.

This species can be distinguished from F. equiseti and other species in the FIESC by the shorter and more robust sporodochial conidia. The apical cell of the sporodochial conidia (i.e., macroconidia) of F. croceum is much less elongated than those of F. equiseti.

Fusarium flagelliforme represents phylo-species FIESC 12 (O’Donnell et al. 2009), a fully supported clade (ML & MP-BS = 100 %; PP = 1.0), closely related to F. longifundum in the Equiseti clade. Similar to F. longifundum, this species lacks conidiophores and conidia on its aerial mycelia, but does produce abundant sporodochia and sporodochial conidia on the carnation leaf pieces and surrounding medium. The sporodochial conidia of F. flagelliforme ((3–)4–5(–6)-septate; 37–85 × 3–5 μm overall) are larger than those of F. longifundum ((3–)5(–6)-septate; 21–76 × 3–5 μm overall). This species appears to be restricted to Europe, mostly associated with cereals.