Its name applies to water moulds of many forms, functions, and host preferences, many of which are actually different species which have not yet been separated and described.

[2][3] Some species previously treated as part of the complex include Phytophthora rosacearum, P. sansomeana, P. sojae, P. medicaginis, and P.

[2] Water moulds in the P. megasperma complex can be found on a multitude of host plants, including many agricultural crops.

It has been noted on soybeans,[4] kiwifruit (Actinidia deliciosa), horse chestnut (Aesculus hippocastanum), hollyhock (Alcea rosea), asparagus (Asparagus officinalis), Brassica oleracea, crops such as cabbage, cauliflower, safflower (Carthamus tinctorius), Port Orford cedar (Chamaecyparis lawsoniana), chickpea (Cicer arietinum), carrot (Daucus carota), carnation (Dianthus caryophyllus), eucalyptus (Eucalyptus spp.

), stone fruit such as apricot, cherry, plum, and peach, Douglas fir (Pseudotsuga menziesii), sugarcane (Saccharum officinarum), and potato (Solanum tuberosum).