Aphanomyces exoparasiticus Coker & Couch 1926

Aphanomyces exoparasiticus Coker & Couch; Couch, Jour
EHsha Mitchell Soc. 41 : 216. 1926.
Mycelium facultatively a semiparasite on threads of other Phy corny cetes, also culturable as a pure saprophyte; hyphae, when growing as a semiparasite, twining about threads of the host and rapidly destroying them; when growing as a saprophyte on vegetable or animal matter in water, much as in A. laevis or A. slellatus, but not so strongly developed; mycelium abundantly developed on cornmeal agar, forming rhizoid-like lateral outgrowths much like those entwining host-threads when growing semiparasitically; sporangia abundant on hempseed, rather sparingly developed when growing as a semiparasite in water, indistinguishable from those of A. laevis or A. scaler; spores 8.1-11.1 m, averaging about 9.3 p thick; sexual organs abundantly developed under most conditions, very numerous on cornmeal agar, fairly abundant when growing semiparasitically on other fungi in water, rarely or not at all developed when growing saprophytically on bits of hempseed or corn-grains in water; oogonia usually borne on lateral stalks, several times as long as the diameter of the oogonia, 28-40 p in diameter, most 33-37 ft, not counting the long, usually pointed, rarely short and blunt, very conspicuous spines, which vary from 5.5-14 p long; spines 10-20 to an oogonium; oogonial wall 1.8-2.5 p thick; eggs single, nearly filling the oogonium, 24-30 p thick, spheric with a large centric or subcentric oildrop surrounded by granular protoplasm, the wall 2-2.5 p thick; antheridial branches diclinous, arising usually from a thread running near base of the oogonial stalk and twining around latter; antheridia either short and tuber-like or often long and wrapping around the oogonia, coming in contact very early with the oogonia, into which they empty their contents; empty antheridia thick-walled and long-persistent.
Type locality: Chapel Hill, North Carolina. Habitat: Semiparasitic on Phycomyceles such as Pythium. Distribution: New York and North Carolina.