Other representative cultures examined: IMI 393171, IMI 393172, IMI 393173, and IMI 1393176 (details in Table 1). UK: Cornwall: Gwennap, Burncoose, ex Fagus sylvatica bark, 2004, C. M. Brasier & A. V. Brown (IMI 1393174, previously P1617/BRN21 in Forestry Commission collection); Trevince, Horse Wood, ex Fagus sylvatica bark, 2004, A. V. Brown & C. M. Brasier (IMI 393175, previously P1797/ HRS03 in Forestry Commission collection).

Previously known informally as Phytophthora taxon C (PtC). Colonies on CA (10 d at 20 x in darkness) largely submerged (Figs 1–4). On subsequent exposure to light, with a small central boss of patchy aerial mycelium (Figs 5–6). In diurnal light, with alternating rings of aerial mycelium (Figs 7–8). Some isolates degenerate during subculturing on artificial media to produce irregular, sectoring colonies or faster striate colonies with lobes of denser aerial mycelium. Optimum temperature for growth on CA (6 isolates, Table 1), ca 18 x. Upper temperature limit for growth (7 isolates, Table 1) ca 26 x. Growth rate at 20 x in darkness ca 3.8–4.6 mm dx1 (mean 4.2 mm dx1 ). Homothallic, gametangia usually frequent to abundant after 10 d on CA (Figs 9–17). Oogonia, diam range of means (4 isolates, Table 1) 23.5–25.5 mm, common range ca 21–28 mm; often with tapered stalks (Figs 10–14, 16). Antheridia amphigynous. Antheridial lengthrwidth range of means ca 11.5–12.5r 10–10.5 mm, common range ca 10–14r9–12 mm. Oospores plerotic, diam range of means ca 21.1–22.5 mm, common range ca 19–25 mm; wall thickness average ca 3.5 mm, common range 3.5–5 mm. Sporangia occasional on CA in the light. Produced abundantly on CA plugs immersed in unsterile pond water or soil leachate; with sympodial sporangiophores. Papillate, caducous, from regular ovoid or limoniform (Figs 18–22) to distinctly asymmetrical or ‘mouse-shaped’ with one rounded and one flatter side (Figs 23–26). Most have a conspicuous vacuole. Sporangia lengthrwidth range of means (4 isolates, Table 1) ca 38.5–45.5r22.5–27 mm, common range ca 34–52r19–31 mm. Length:width ratio average ca 1.5 mm. Sporangial pedicels range of means ca 8.6– 14.1 mm, common range ca 5–19 mm. Hyphae sometimes denticulate or tuberculate. No chlamydospores observed.

Phytophthora kernoviae differt ab aliis speciebus papillatis per suam combinationem characterum; systema sexus homothallica; oogonia saepe cum base attenuata, diam. in medio ca 21–28 mm; antheridia semper amphigynosa, in medio ca 10–14r9–12 mm; sporangia papillata, saepe cum vacuola conspicua, decidua cum pedicellulibus brevibus (in medio ca 5–19 mm); longitudo et altitudo sporangiorum ca 34–52r 19–31 mm; temperaturae crescentiae in agaro ‘carrot agar’, optima ca 18 xC (incrementum radiale ca 3.8–4.6 mm per diem) et maxima ca 26 x; coloniae in agaro ‘carrot agar’ in tenebris saepe ex parte submersae.

UK: Cornwall: Caerhays, isol. ex Fagus sylvatica bark, Jan. 2004, C. M. Brasier (IMI393170 – holotypus). [Dried culture on carrot agar; previously Forestry Commission Phytophthora culture collection isolate P1571]