Phytophthora tentaculata Kröber & Marwitz was described in 1993 in Germany on greenhouse-grown nursery ornamentals. It has since been found in Italy, Spain, China and the U.S. (California) causing a root and stem rot of many different plant species including nursery-grown native species used for habitat restoration. P. tentaculata is homothallic and is classified in Stamps group I which is characterized by the production of mostly paragynous antheridia, papillate sporangia and the production of both hyphal swellings and chlamydospores in culture. P. tentaculata is placed in phylogenetic Clade 1 (Cooke et al., 2000) with species such as P. cactorum, P. nicotianae, P. clandestina, P. iranica, P. hedraiandra and P. pseudotsugae.
Etymology: refers to the spider web-like growth habit of the mycelium in culture.
Sporangia of P. tentaculata are spherical or ovoid to obpyriform, papillate to occasionally bipapillate and measure 10-81 x 13-52 mm (average 35.7 x 27.4 mm). They are primarily noncaducous, rarely caducous with a short pedicel, and often have elongated necks or beaks. Small hyphal swellings are intercalary and often occur with hyphal branching. On PARP and V8 juice agar, the hyphal growth pattern resembles a non-organized web spun by spiders in the family Theridiidae; hyphae often grow forming loops in the agar. Chlamydospores are intercalary to terminal, thin-walled, measuring 10-45 mm (average 26.6 mm), occasionally with a short hyphal projection. P. tentaculata is homothallic, with mostly paragynous antheridia. Antheridia are diclinous and often form tooth-like projections when they encircle the oogonia. Oospores are spherical, aplerotic, and measure 14-38 mm (average 28.1 mm) (Erwin and Ribeiro, 1996; Kröber and Marwitz, 1993).