Benin. Collines: Glazoué, c. 189 m a.s.l., 7°58’ 25"N, 2°14'24"E, on Zornia glochidiata DC. (Fabaceae), 22 Sep 2019, Y. Meswaet, A. Tabé and M. Piepenbring, YMM299 (Holotype: M-0312659; Isotypes: UNIPAR) . Ex holotype sequences.MW848616 (tef1).

The epithet zorniicola refers to the host genus Zornia and “-cola” (lat. colere = to dwell).

Cercospora zorniicola is characterised by external hyphae, unbranched conidiophores that are uniform in colour and width, with mostly monoblastic conidiogenous cells (Fig. 13).

Leaf spots almost lacking or brown to dark brown discolorations, amphigenous, 0.5–2 mm diam., often located along the main veins, surrounded by a yellow discoloration of undefined size and shape. Caespituli amphigenous, greyish brown to dark brown. Mycelium internal and external. External hyphae 2–3 μm wide, septate, branched, subhyaline to pale olivaceous, smooth. Stromata lacking or formed by few substomatal aggregated swollen hyphal cells, up to 22 μm wide, in substomatal chambers or embedded in the mesophyll, dark brown. Conidiophores in small, loose fascicles of up to approx. 14 conidiophores, arising from internal hyphae breaking through the adaxial epidermis of the leaves, or penetrating through stomatal openings, occasionally solitary arising from external hyphae, erect, straight, subcylindrical to geniculate, unbranched, (15–)24.5–134(–158) × 3.5–4.5 μm, 1–5(–6)-septate, brown to dark brown, often uniform in colour and width. Conidiogenous cells usually monoblastic, rarely polyblastic; loci 1.5–3 μm wide, thickened and darkened. Conidia solitary, acicular to narrowly obclavate, straight to curved, (15–)27.5–182.5(–200) × (2–)2.5–3.5(–4) μm, 1–8(–12)-septate, hyaline, tip acute, base truncate to short obconically truncate, 1.5–3 µm wide, hila thickened and darkened.

Benin. Borgou: Parakou, on the way to N’Dali, c. 367 m a.s.l., 9°27'53"N, 2°37'43"E, on Zornia glochidiata, 17 Sep 2019, Y. Meswaet and R. Dramani, YMM13 (Paratypes: M-0312660; UNIPAR). Benin. Borgou: Parakou, c. 391 m a.s.l., 9°22'56"N, 2°37'33"E, same host, 29 Aug 2019, Y. Meswaet and A. Tabé, YMM233 (M-0312661).

The genus Zornia comprises 80 species mainly distributed in tropical regions of the world (Fortuna-Perez et al. 2013). No species of Cercospora are currently known on hosts belonging to Zornia (Farr and Rossman 2021). Pseudocercospora zorniae (J.M. Yen & Gilles) Deighton (≡ Cercospora zorniae J.M. Yen & Gilles) is the only known species of cercosporoid fungi infecting species of Zornia.

In the multi-gene phylogeny (Fig. 1), Cercospora zorniicola grouped closely, but with poor support, with isolates of Cercospora cf. citrullina (MUCC 576) on Citrullus lanatus (Thunb.) Matsum. & Nakai (Cucurbitaceae) and C. kikuchii on Glycine max, Phaseolus spp., Cyamopsis tetragonoloba (L.) Taub., Vigna and other Fabaceae hosts (Mulder and Holliday 1975; Groenewald et al. 2013). However, morphologically, C. zorniicola is clearly distinct from C. cf. citrullina by external hyphae, unbranched, darker and longer conidiophores [(15–)24.5–134(–158) μm] and somewhat longer conidia [(15–)27.5–182.5(–200) μm], while C. cf. citrullina has pale to pale brown and short conidiophores (50–86 μm) and shorter conidia (40–130 μm) (Groenewald et al. 2013). C. zorniicola differs from C. kikuchii in having external hyphae, darker and shorter conidiophores [(15–)24.5–134(–158) μm] and shorter conidia [(15–)27.5–182.5(–200) μm], while C. kikuchii has paler and longer conidiophores (45–200 μm) and above all, much longer conidia (50–375 µm) with numerous indistinct septa (Mulder and Holliday 1975; Hsieh and Goh 1990). In the phylogeny based on tef1 molecular sequence data, it is not possible to distinguish C. zorniicola from other Cercospora spp. (see Suppl. material 4).

Based on a MegaBLAST search in the NCBI GenBank nucleotide database using the tef1 sequence data of C. zorniicola, the closest matches were Cercospora aff. canescens on Dioscorea rotundata Poir. (Dioscoreaceae) from Ghana (GenBank JX143316; Identities 294 / 300, i.e., 98%), Cercospora cf. coreopsidis W.W. Ray on Coreopsis lanceolata L. (Asteraceae) form South Korea (GenBank JX143344; Identities 293 / 300, i.e., 97%) and Cercospora nicotianae on Nicotiana tabacum (Solanaceae) from China (GenBank MK881748; Identities 292 / 300, i.e., 97%). This species is proposed to be new to science based on a distinct combination of morphological characteristics and because no other species of Cercospora is currently known on a species of this host genus.