Pythium porphyrae has a
mycelial thallus that is
eucarpic, meaning only part of the thallus turns into
sporangia. and are not
septate. On algae, the hyphae will extend through the cell wall. It does not have
haustoria not
chlamydospores. The
appressoria are club-shaped. It has sporangia that are unbranched, filamentous, and non-inflated, typically forming 6–17
zoospores per vesicle.
Encysted zoospores are 8–12 μm in diameter. Hyphal swellings are
intercalary and
globose, from 12–28 μm in diameter.
Oogonia average 17 μm in diameter and are also intercalary and globose, but rarely are terminal. In each oogonium are 1–2
diclinous antheridia coming out far away from the oogonial stalk. The antheridia's cells are
clavate (club shaped) or globose. The antheridia will be
apical to the oogonial wall. Sometimes there will be two antheridial cells on one stalk. The
yellowish
oospores average 15 μm in diameter, have thick (~2 μm) walls, and are
plerotic (fill the whole oogonium).
Conidia are spherical at 8.8–30.8 μm diameter, but rarely produced.
Pythium porphyrae shares many physical traits with
P. marinum and
P. monospermum, and appears to be most closely related to
P. adhaerens. However it has up to four diclinous antheridia and sometimes two antheridial cells per stalk;
P. monospermum has 1–4 either diclinous or
monoclinous antheridia and
P. marinum has only a single diclinous antheridium.
P. monospermum and
P. marinum also have oogonia terminally on short branches, yet in
P. porphyrae they tent to be intercalary. In a
laboratory it will grow 5 mm per day on
seawater-cornmeal agar with low aerial
mycelium and colorless colonies, but will not grow at all on
potato-carrot agar. ==Ecology==