sequence data ofC. clavulifera(D Hudspeth
and M Hudspeth pers. commun.).
- Leptomitales s. lat. and Related
Clades
In theLeptomitales(Fig.3.8) only members of
the familyLeptomitaceae(Table3.5) have been
sequenced to date. This family includes the
generaApodachlya (Fig.3.8f),Apodachlyella
(Fig. 3.8g–i) and Leptomitus (Fig. 3.8d, e),
which are commonly known assewage moulds
because they are frequently isolated from pol-
luted or organic-rich water and have the capa-
bility offermentative nutrition(Dick1973a;
Gleason 1976 ; Riethmu ̈ller et al. 2006 ).Lepto-
mitushas also been reported as an opportunist
necrotrophic pathogen of perch (Willoughby
and Roberts 1991 ). They produce eucarpic
mycelial thalli (Fig.3.8d, f, g) which have con-
stricted hyphae plugged with granules ofcellu-
lin, a unique chitin-glucan polymer (Huizar
and Aronson 1986 ; Lee and Aronson 1975 ).
Oogonia in the Leptomitaceae are usually uni-
oosporiate (Fig.3.8e).Apodachlyahas a dis-
tinctive oospore with a single large fused lipid
globule pushing against a large optically trans-
lucent ooplast vacuole (Fig.3.8e) (Dick 1969 ).
The two sequenced species,Apodachlyaand
Leptomitus, form a well-supported monophy-
letic clade deeply separated from the Saproleg-
niales (Fig.3.5) (Petersen and Rosendahl 2000 ).
The related genusApodachlyella(Fig.3.8g–i)
was transferred by Dick ( 1986 ) to its own
monotypic family, the Apodachlyellaceae
(Table3.4). This genus produces an elongate
antheridium (Fig. 3.8h) containing cyst-like
male gametangial units (Fig.3.8i). Longcore
et al. ( 1987 ), however, questioned whether this
difference merited the reassignment ofApoda-
chlyellato a family of its own and suggested it
should be retained in the Leptomitaceae.
Dick (2001a) included in his revised Lepto-
mitales two additional families (Table3.4), the
Ducellieraceae(Hesse et al. 1989 ) andLeptoleg-
nielliaceae(Fig.3.8j–x), for which there are as
yet no formally published sequence data.Ducel-
lieriais a monotypic genus that infects pollen
grains and was originally thought to be an alga
(Hesse et al. 1989 ). The familyLeptolegniella-
ceaecontains mostly holocarpic genera, such as
Aphanomycopsis, a genus that infects algae
(Fig.3.8l) and insect eggs (Fig.3.8m) (Karling
1981 ). The taxonomically problematic oomy-
cete hyperparasite Pythiella(Blackwell 2010 )
(Fig.3.8r–x) has centrifugal sporogenesis and
an aphanomycoid pattern of zoosporogenesis
similar to Aphanomycopsis, which suggests
that this genus may also be part of the Leptoleg-
niellaceae, despite its reportly having periplas-
mic oogenesis (Fig.3.8v–x).
The holocarpic genusCornumyces(as illu-
strated byLagenidium pygmaeumwhich Dick
transferred toCornumyces) (Fig.3.8j–k), which
colonizes pollen grains, forms a separate clade
with affinity to the ~Leptomitales clade (Inaba
and Hariyama 2006 ). This supports Dick’s
(2001a) tentative placement ofCornumycesin
the Leptolegniellaceae. Inaba and Beakes
(unpublished data) also found that the genus
Cornumyces formed a monophyletic clade
(based on SSU rRNA sequences), together
with the holocarpic nematode-infecting genus
Chlamydomyzium (Fig.3.8n–q). This genus,
which Dick ( 1997 ) had originally placed in his
newly created Myzocytiopsidales but later con-
sidered asincertae sedis(Dick2001a), has been
shown to be an early-diverging saprolegniomy-
cete (Beakes et al. 2006 ; Glockling and Beakes
2006b). Environmental sampling has revealed
that both an unknown marine stramenopile
(MAST) clade (Massana et al. 2002 , 2004 , 2006 )
and a number of freshwater isolates from kera-
tin baits (Inaba, unpublished) also fall in clades
that diverge near these Leptomitales s. lat.
clades. Until there is far greater taxon sampling
within theLeptomitaless. lat., it is proposed
that those genera with eucarpic constricted
thalli be placed in theLeptomitaceaeand all
those with nonmycelial thalli, includingDucel-
laria, be included within an expanded ~Lepto-
legniellaceae until sequence data become
available (Fig.3.6, Table3.5).- Saprolegniales
Saprolegniales includes many of the familiar
and relatively well-studied genera (Figs. 3.9,Systematics of the Straminipila: Labyrinthulomycota, Hyphochytriomycota, and Oomycota 59