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Perithecia
(singular: perithecium): globose to flask-like
ascomata
where the
hymenium
is
enclosed within a “box” opening through a narrow apical pore at the summit, called
ostiole
.
Perithecioid
(of apothecia): opening through a pore, hence
disc
not evident and the whole
structure resembling a
perithecium
(e.g.
Pertusaria pertusa
). In a few cases, it might be very
difficult for a beginner to distinguish between a true perithecium and a perithecioid
apothecium (e.g. in
Belonia russula
). In such cases, the species also appears in the keys
among those having perithecia.
Photobiont
: the photosynthetic partner of a lichen. In our keys three main types of photobionts
are used for identification:
cyanobacterial
,
chlorococcoid
, and
trentepohlioid
.
Phyllidia
(singular: phyllidium): flattened structures resembling small lobes, formed by
abstriction of a leaf-like part of the thallus, and serving for the vegetative reproduction of the
lichen; they are sometimes difficult to distinguish from flattened
isidia
; this term is used
very seldom in our keys.
Phyllocladia
(singular: phyllocladium): minute, granular, verrucose to coralloid, peltate to
digitate parts of the thallus of
Stereocaulon
, bearing the
photobiont
.
Pigmented
: coloured, not white nor transparent in section.
Placodioid
(of crustose thalli):
orbicular
, with radiating marginal
lobes
. A difficult, not
indispensable term of the lichenological terminology.
Placodiomorph
(of crustose thalli): see
placodioid
.
Plectenchyma
(of thallus sections): a general term for all false tissues formed by the mycobiont
only. See also
paraplectenchymatous
,
prosoplectenchymatous
.
Pluricellular
(of spores): many-celled.
Podetia
(singular: podetium): lichenised, fruticose structures of
Cladonia
and a few related
genera, ontogenetically developing from a vertical extension of the lower apothecial tissues.
Most of the
Cladonia
have two types of thallus: a primary, crustose to squamulose thallus,
and the "podetia". However, a beginner might wonder whether the thalli of e.g.
Dactylina
ramulosa
or
Thamnolia vermicularis
are "podetia" or not. As far as possible, we have tried
to use this term only within
Cladonia
. See also
pseudopodetia
.
Polar-diblastic
(of spores): two-celled, the cells being connected by a narrow canal (most
Teloschistaceae
), whose length may be important for identification.
Polymorphic
: of different forms.
Primary
(of thallus parts): some fruticose lichens (especially
Cladonia
) have two types of
thallus
: the primary one,
crustose
or
squamulose
, gives origin to
fruticose
structures
(
podetia
and
pseudopodetia
). In this book the term “primary squamules” exclusively refers
to those of
Cladonia
, while the term “primary thallus” also refers to other genera in which
podetia
or
pseudopodetia
originate from a crust-like thallus (e.g.
Baeomyces, Stereocaulon
).
The term “primary” has to do with the ontogeny of of thallus parts, non-primary structures
(like
podetia
) developing from the generative tissue of the
apothecia
, a character which is of
no use for identification.
Proliferating
(of podetia): formed on the centre (e.g. in
Cladonia verticillata
) or on the margins
(e.g. sometimes in
Cladonia pyxidata
) of
cups
, giving rise to one or several stocks of
podetia
.
Propagule
: any structure serving to reproduce the lichen. Mostly used for those related to
vegetative reproduction (
soredia
,
isidia
,
thalloconidia
, etc.). See also
diaspore
.
Proper
(of apothecial margin): see
margin
.
Prosoplechtenchymatous
(of thallus sections): fungal tissue consisting of coalesced, more or
less elongated hyphal cells; see also
paraplectenchymatous
.
Prothallus:
marginal part of the
thallus
of crustose lichens, composed only by the fungus,
normally with a different colour and texture
.
In some cases (e.g.
Placynthium nigrum
) it is
rather thick and felt-like, in other cases (e.g.
Rhizocarpon
species growing on quartz) it
