Systematics and Evolution, Part A The Mycota

Brachyallomyces(Emerson 1941 ). Emerson found
that by varying the substrate he could induce some
putativeBrachyallomycesisolates to form gameto-
phytes, and he was careful to ascribe only those
isolates that remained consistently asexual to the
subgenus. It was later revealed that asexuality was
maintained by mitosis in the resistant sporangia of
someA. anomalusisolates (Fig.7.6e), while in
other isolates meiosis was presumably followed
by endomitosis (nuclear replication without divi-
sion) in germinating meiospores to reestablish the

diploid condition (Fig.7.6f) (Wilson and Flanagan

1968 ). The sporophytic thalli ofA. anomalusiso-

lates are entirely like those ofEuallomycesspecies

but lack a sexual stage.

C. Life Cycles of Other Blastocladiomycota

In the 70 years since the publication of Emer-

son’s monograph onAllomyces, many new blas-

toclads have been discovered, and the diversity

Fig. 7.5(a–m) Life cycle ofAllomyces neo-monilifor-
mis.(a) Germinating resistant sporangium with rup-
tured outer wall and swollen inner wall with two
discharge papillae. (b) Beginning of meiospore release.
(c) Biflagellate meiospores exiting resistant sporan-
gium; some have encysted. (d) Cysts, each with single
papilla, clustered at mouth of empty resistant sporan-
gium. (e–h) Stages in emergence of uniflagellate
gametes from cysts; syngamy not shown. (i) Germina-

tion of encysted zygotes. (j, k) Young thallus (j) devel-

ops into mature sporophytic thallus (k) bearing

resistant sporangia (R) and thin-walled zoosporangia

(Z). (l) Release of zoospores from thin-walled zoospor-

angia. (m) Germination of encysted zoospore to form

young thallus (j). Drawing from Emerson ( 1941 ), used

with permission from Lloyd Library and Museum;

American Society of Pharmacognosy

Blastocladiomycota 189