Anatomical Features of Chondropsis Semiviridis (Nyl.) Nyl. in Relation to its Vagrant Habit

Abstract

The anatomy of Chondropsis semiviridis (Nyl.) Nyl. shows adaptations to a vagrant life form and sub-arid habitat. The differential swelling of the thick upper cortex and the medulla is responsible for the rolling movement of the thallus under successive wet and dry conditions.

Full text

Lichenologist
20(1):
25-29 (1988)
ANATOMICAL FEATURES OF CHONDROPSIS
SEMIVIRIDIS (NYL.) NYL. IN RELATION
TO ITS VAGRANT HABIT
H. T. LUMBSCH* and H. W. KOTHE*
Abstract: The anatomy of Chondropsis
semiviridis (Nyl.)
Nyl.
shows adaptations
to a
vagrant life form and sub-arid habitat. The differential swelling of the thick upper
cortex and the medulla is responsible for the rolling movement of the thallus under
successive wet and dry conditions.
Introduction
Among the unattached lichens two groups can be distinguished. The non-
obligatory unattached lichens, which are normally in connection with their
substratum and the obligatory unattached lichens, which are exclusively terri-
colous. According to Biidel & Wessels (1986), the facultatively unattached
lichen species should be called erratic, while the term for the latter should be
vagrant. In the early literature these terms are used as synonyms (Rogers 1977,
Weber 1977). Vagrant lichens are known from windswept steppes and deserts
all over the world, for example Xanthoparmelia
chlorochroa
(Tuck.) Hale in
Wyoming or Xanthomaculina convoluta (Hue) Hale in the Namib Desert
(Weber 1977). Hygroscopical movement of the thallus has been described in
the latter species (Biidel
&
Wessels 1986). A similar rolling movement of the
thallus when drying or wetting is known from
Chondropsis semiviridis
(Nyl.)
NyJ.
and such
lichens
are
caJJed
hygrochasic vagrants (Rogers
1971,1977).
The
anatomical structures responsible for this movement are described in this
paper.
Two species of the genus
Chondropsis
Nyl. (Parmeliaceae) are known, i.e.
C.
semiviridis
and C.
sorediata
Elix
&
Child (Elix
&
Child 1986). C.
semiviridis
las an Australasian distribution (Galloway 1980, Rogers & Lange 1972).
C.
sorediata
is sympatric but rarer and more scattered in its distribution. The
phytosociology and the influence of environment on the distribution of
C.
semiviridis
was investigated by Rogers (1972a, b).
Material and Methods
Specimen
examined:
New Zealand, South Island, Central Otago, Alexandra, on soil in steppe,
.985,
Henssen
&
Lumbsch
30393 (MB).
Light
microscopy:
Thalli were examined histologically with the aid of a freezing microtome. The
iections (14 nm) were stained in lactophenol-cotton blue.
Scanning electron microscopy
(SEM): Lichen thalli were fixed in 37% formalin/100% acetic
icid/70% ethanol (0-5:0-5:9) for about
6
h and then washed in three changes of
tap
water. There-
ifter they were dehydrated according to Samson et
al.
(1979). Critical point dried specimens were
nounted on stubs and sputter-coated with gold. To examine the anatomy of dry thalli, air-dried
ipecimens were mounted and coated with gold. The specimens were examined in a Leitz AMR
1200 B
SEM.
•Fachbereich Biologie der Philipps-Universitat, Karl von Frisch-Strasse, D-3550 Marburg/
Lahn, F.R.G.
W24-2829/88/010025 + 05 803.00/0 © 1988 British Lichen Society

to
X
n
S3
w
o
r
o
o
H
o
FIG.
1. C
semiviridis.
A, thallus in dry state; B, thallus in wet state; C, longitudinal section; D, longitudinal section showing the lower cortex. Scales: "
A-B
=
50mm;C-D
=
g

1988Chondropsis—Lumbsch & Kothe 27
Results
The dichotomously branched thalli of
C.
semiviridis
lack
rhizines.
The appear-
ance of
the
species when dry is quite different from when it is wet. In the dry
state the lower surface of the thallus
is
visible and the lichen resembles
a
ball,
as
the lobes are
recurved
(Fig.
1
A).
When
wet,
the thallus spreads outflat
(Fig.
IB).
The lichen increases from 5-10 mm in diameter when dry to 10-35 mm when
wet.
The thallus is covered by a thin epicortex (Fig. 1C). The upper cortex is
prosoplectenchymateous, composed of hyphae with thickly gelatinized walls.
This layer varies in thickness from 80 to 100 nm. The algal layer is located
FIG.
2.
C.
semiviridis
(SEM).
A, Longitudinal section of thallus in dry
state;
B,
longitudinal section
of thallus in wet state. Scales =
100
nm.

28 THE LICHENOLOGIST Vol. 20
between the upper cortex and the medulla. The medulla, 100-120 fim thick, is
composed of mostly perclinally-arranged hyphae with gelatinized walls. The
lower cortex is quite thin (Fig. ID) with short-celled hyphae without any
obvious arrangement. The lower cortex is dark in section because of crystals
which are attached to it.
The difference between the wet and dry thalli when sectioned is obvious
(Figs
2A-B).
While the medullary layer
does
not show any conspicuous change,
the upper cortex is very denseley packed in the wet state as a result of the
swelling hyphae.
Discussion
The different swelling capacity of the upper cortex and the medullary layer is
responsible for the rolling movement. The medulla, with loosely packed
hyphae, is able to tolerate the increasing volume of
the
hyphae caused by their
swelling and does not change shape to any extent. However, this
is
not possible
in the more densely packed upper cortex, where interstices between the hyphae
are lacking, even in the dry
state.
Consequently the upper cortex expands more
than the medulla and unrolling takes
place.
A
comparison of
C.
semiviridis
with
Xanthomaculina convoluta
reveals that the anatomy of the latter species is more
complex (Budel & Wessels 1986): the upper cortex is differentiated into an
upper and lower layer and the algal layer and medulla penetrate into the
upper cortex as intrusions, which these authors interpreted as hinges. Our
observations on C.
semiviridis
indicate that these intrusions in
Xanthomaculina
could prevent the bending of the thallus. Such bending has been observed in
Chondropsis,
where a reflexed rather than a
flat
thallus is formed when moist.
Observations of movements in other lichens are rare. Jahns et al. (1976)
reported hygroscopical movement of the soralia of
Hypogymnia physodes
(L.)
Nyl. which was explained as due to a difference in water uptake between the
cortex and the surface of the soralia. The cortical structure of
Chondropsis is
an
adaptation surely not only to the rolling movement but also to the exposed
habitat of the lichen. Relatively thick upper cortices are observed in many
lichens from exposed habitats and are hypothesized to protect the photobiont
against harmful light
intensities.
Thick upper cortices
are
known
to be
environ-
mental modifications within one species (Kershaw 1985), but are constant
characteristics of a number of other genera (Filson 1978, Culberson &
Culberson
1981,
Hale 1985). In C.
semiviridis
the breadth of the lobes can be
correlated with annual rainfall (Rogers 1977), but the thickness of the cortex
is independent of environment in which the species lives and exhibits its
interesting vagrant live form.
We wish to thank Professor Dr
A.
Henssen for her interest in our studies, and Dr
B.
Hayward for
his comments
on
our manuscript. The
first
author
is
indebted
to
the
late
Mr
P.
Child and especially
Mr R. Elder for their companionship during lichen collecting in Central Otago.
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Accepted for publication
8
August
1987