providing evidence that Halophytophthora
s. str. species might also be important for nutri-
ent cycling in temperate marine ecosystems.
~Halophytophthoraspp. have ovoid to elongate
sporangia, often with conspicuous papillar
plugs (Nakagiri2002b), and most show a tran-
sient vesiculate discharge of their zoospores
(Fig.3.15e). Homothallic sexual reproduction
has only been reported to date in approxi-
mately half the known species. All have single
oospored oogonia with mostly paragynous
antheridia(as in Fig.3.15c) (Nakagiri2002b).
Although extensive sequencing of species within this
genus has been reported in conference abstracts or
presented online (e.g. by Nakagiri2002a; Coffey and
Levesque and colleagues), only relatively limited data
have actually been published in the peer-reviewed liter-
ature (e.g. Go ̈ker et al. 2007 ; Hulvey et al. 2010 ). Naka-
giri (2002a) was the first to report that the
Phytophthora-Peronosporaclade was close to a group
ofHalophytophthoraspp. and formed a sister clade to
what he referred to as theH. vesiculacomplex. He also
noted thatH. spinosaseemed to be only distantly
related to otherHalophytophthoraspecies in a clade
close toSapromyces, which makes it possible that this
species belongs to the Salispilaceae described by Hulvey
et al. ( 2010 ). The type speciesH. vesicula(Ho and Jong
1990 ) is part of a monophyleticHalophytophthoras. str.
clade, which also includesH. avicenniae,H. batema-
nensis, andH. polymorphica.The mainPhytophthora-
downy mildew clade itself includes a number of species,
such asH. elongata,H. exoprolifera, andH. porrigove-
sica(Coffey et al. 2011 ).Yet other species are to be
found dispersed amongstPhytopythiumandPythium
clades (Coffey et al. 2011 ). For instance,H. kandeliaeis
nested within thePhytopythiumclade, andH. episto-
miumseems close toPythium monospermum. Thus,
Halophytophthoraas previously circumscribed is a
good example of how ecological preference, which
might also lead to convergently evolved morphological
traits, is mostly not useful for group delimitation in a
taxonomic sense.
(v) Part 2:PhytophthoraClades
This section of thePeronosporaceaeincludes
some of the most highly adapted and devastat-
ing plant-pathogenic oomycete species. The
facultatively biotrophic genus ~Phytophthora
(Fig. 3.15f–j) is most likely paraphyletic
(Cooke et al. 2000 ; Runge et al.2011a) and
contains over 100 species, which typically pro-
duce ovoid to ellipisoidal sporangia, often on
aerial sporangiopores (Fig.3.15f–h) and single-
oospored oogonia, many of which have distinc-
tive collar-like amphigynous antheridia
(Fig.3.15i, j). Many of the characters that were
once thought to be important inPhytophthora
taxonomy (Sparrow1973c; Waterhouse 1970 ,
1973 ), such as amphigynous (as inPh. erythro-
septica) (Fig. 3.15i, j) versus paragynous
antheridial attachment (as in Pythium)
(Fig.3.14t) and the genetic breeding system
(homothallic versus heterothallic), have not
proved to be good indicators of phylogenetic
relatedness. Most Phytophthora species have
been sequenced (Blair et al. 2008 ; Briard et al.
1995 ; Cooke et al. 2000 ;Fo ̈rster et al. 2000 ;
Kroon et al. 2004 , 2012 ; Martin and Tooley
2003 , 2008 ), and the genus has been divided
into nine or ten monophyletic subclades
(groups 1–10). The morphological characteris-
tics and species composition of these groups
were recently reviewed by Kroon et al. ( 2012 ).
There does not seem to be a unique set of
morphological characters (synapomorphies)
that can be linked with a single clade, although
developmental trends can be associated with
groups of Phytophthora clades (Blair et al.
2008 ; Kroon et al. 2012 ; Runge et al.2011a).
Species in thepresumed basal clades(clades
6–10) are necrotrophic soil-borne pathogens
that produce non-caducous, generally non-
papillate sporangia that release zoospores
upon germination (as in Ph. sojae, clade 7,
Fig.3.15f). This group includes important root
and woody stem pathogens such asPh. cinna-
momi(Hardham 2005 ; Newhook and Podger
1972 ) and Ph. ramorum (Davidson et al.
2003 ). Species in clades 1, 2, 4, and 5 seem to
be more derived and often have an extended
biotrophicphase, produce papillate airborne,
deciduous sporangia, and are predominantly
foliage pathogens, for examplePh. infestans
(Fig. 3.15g, h, clade 1) and Ph. palmivora
(clade 4) (Kroon et al. 2012 ; Runge et al.
2011a). Species in the more derived lineages,
especially clade 4, are more difficult to isolate
and culture, and some even appear to beobli-74 G.W. Beakes et al.