ever, the possibility that Albuginales-like oos-
pores associated with fossils might be derived
from an extinct organism unrelated to white
blister rusts with convergent traits cannot be
ruled out.
Papillate, multi-oospored oogonia, remi-
niscent of those found in present-day Saproleg-
niales, have also been described in similar
Rhynie chert deposits from the same time
period (Krings et al. 2010 ). Another fossil
genus,Combresomyces, having spiny papillate
oogonia with paragynus antheridia, resembling
present-day Pythium species, was recently
described as being associated with the remains
of a 300 mya seed fern,Lygniopteris(Strullu-
Derrien et al. 2010 ).Galteriella biscalitheceae,
associated with a sporangium of a fernBiscal-
litheca, also from around ca 300 mya, has
amphigynous and paragynous smooth-walled
oogonia. Therefore, it seems that by the early
Mesozoic era(ca. 300 mya) all fossils showing a
range of oogonium morphologies similar to
those found today in the Albuginales, Peronos-
porales, and Saprolegniales have been docu-
mented, which implies that much of the
oomycete diversity we know of today, with
most likely the exception of the hyperdiverse
downy mildews, had evolved by that period.
There are other remarkableevolutionary
parallels between the fungi and oomycetes.
The early-diverging chytridRozellahas endo-
biotic plasmodial thalli and microsporidia have
an injecting infection mechanism (Jones et al.
2011 ; Lara et al. 2009 ) that are reminiscent of
EurychasmaandHaptoglossarespectively. The
clade (MAST-1) of unknown marine strameno-
piles that are closest to the oomycetes (Seki-
moto 2008 ; Yubuki et al. 2010 ) may be
analogous to the recently described cryptofun-
gal clade that seems to be the sister clade to the
Fungi (Jones et al. 2011 ). This highlights that
many phylogenetically critical organisms
remain to be discovered and described, and
we still have little idea what sort of organisms
make up unknown MAST clade stramenopiles.
They are probably being sampled from their
zoospores, and many may be parasitoids or
parasites.
V. Conclusions
Since the last account of these groups (Dick
2001b) the application of molecular systematics
has greatly improved our understanding both
of how individual members of the stramenopile
clade relate to each other and to the wider
eukaryote community. The marine origin of
all the osmotrophic stramenopiles is also now
evident. Labyrinthulomycota, Hyphochytrio-
mycota, and Oomycota, together with the
ochrophytes, share a common ancestor, which
was most likely a photosynthetic mixotrophic
flagellate (Tsui et al. 2009 ). The Labyrinthulo-
mycota are part of one major stramenopile line,
and the Hyphochytriomycota s. str. and Oomy-
cota are part of another. If environmental
marine sequences are included in analyses, it
becomes apparent that the Hyphochytriomy-
cota s. str. and Oomycota are probably not as
closely related as originally thought (Beakes
1987 ). The largest and ecologically most impor-
tant group are the oomycetes, which because of
their economic importance have been much
more extensively studied than the other groups.
Since the last taxonomic synthesis it has
become clear that a number of early-diverging
clades lie outside of the two main galaxy clades
proposed by Sparrow ( 1976 ). Nearly all early-
diverging genera are marine, holocarpic para-
sites of invertebrates and algae, with relatively
broad host ranges.
The migration of oomycetes from the sea to
the land probably occurred around the time the
Saprolegniomycetes and Peronosporomycetes
diverged and coincided with the evolution of
eucarpic thalli and sexual reproduction by
means of oogonia and antheridia. The transi-
tion to freshwater and terrestrial ecosystems
also seemed to bring about a broadening of
the ecological niches that oomycetes occupied,
from species that were general saprotrophs to
those that became specialized obligate bio-
trophs. It is possible that these arose from
ancestral species that were broad-spectrum fac-
ultative parasites of either arthropods or algae.
Finally it is clear that, compared with Fungi,
oomycete systematics is still very much a work
in progress. Many of the phylogenetically criti-84 G.W. Beakes et al.