Content uploaded by Jean Claessens
Author content
All content in this area was uploaded by Jean Claessens
Content may be subject to copyright.
Jour.Eur.Orch.
30 (3): 629 - 637. 1998.
Jean Claessens and Jacques Kleynen
Column structure and pollination of Corallorrhiza trifida
Châtelain (Orchidaceae)
Keywords
Corallorrhiza trifida, Orchidaceae, stipes, hamulus, autogamy.
Zusammenfassung
Claessens,J. & J.Kleynen (1998): Column structure and pollination of
Corallorrhiza trifida Châtelain (Orchidaceae).-Jour.Eur.Orch. 30(3): 629-637.
Corallorrhiza trifida
b
esitzt eine typische Säulchenstruktur, wodurch die
Autogamie ermöglicht wird. Das Rostellum bildet eine hackenförmige
Verlängerung, der Stipes (vom Hamulus- Typ). Die vier Pollinien werden mittels
vier dünnen, elastischen Pollenstielchen mit dem Stipes verbunden.
An der Basis vom Stipes befindet sich das Viszidium, das aber nur sehr kurze
Zeit, noch vor der Anthese, funktioniert. Die Selbstbestäubung, die bei
C.
trifida
die Regel ist, wird ermöglicht, indem die Antherenkappe austrocknet und sich
gleichzeitig erhebt. Die Pollinien fallen dann, fest verbunden mit den elastischen
Pollenstielchen, auf die Narbenfläche, wo sie kleben bleiben.
Summary
Claessens,J. & J.Kleynen (1998): Column structure and pollination of
Corallorrhiza trifida Chatelain (Orchidaceae).-Jour.Eur.Orch. 30(3): 629-637.
Corallorrhiza trifida has a particular column structure, which facilitates
autogamy. The rostellum forms a hook-like prolongation, the stipe (of the
hamulus-type). The four pollinies are connected to the rostellum by means of four
thin, elastic caudic1es.
There is a viscidium at the base of the stipe, which functions only a very short
time, before anthesis. Autogamy, which is general practice with
C.
trifida, is
realised by the simultanious dessication and lifting of the anther cap. This
Journal Europäischer Orchideen 30(3): 1998. 629
viscidium (an assumption that is false, as we will point out later), they can neither be
attached to a visitors head nor to a pencil tip.
KIRCHNER (1922) observed, how the anther cap drops off very easily, thus allowing
the pollinies to fall, passing both sides of the very small rostellum, right onto the
nearby stigma. Descriptions of later authors, e.g. SUMMERHA YES (1951), DAVIES
et al (1983) and LANG (1989) are based upon the observations of KIRCHNER and do
not bring any new knowledge as far as the process of autogamy is concerned.
They too report about visiting insects: SUMMERHAYES (1951): hoverflies and other
small insects
(Hymenopteres); LANG (1989) too observed hoverflies and dungflies
(Scatophaga). But very important is the fact, that none of the authors could actually
observe, whether the visitors were actual pollinators.
enables the pollinies, firmly joined to the caudicles, to fall on the stigmatic surface,
where they keep sticking.
Claessens, J. & J. Kleynen (1998): Column structure and pollination of Corallorrhiza
trifida
Châtelain (Orchidaceae).-Jour. Eur. Orch. 30(3): 629-637. La structure du
gynosteme de
Corallorrhiza trifida est bien typique pour l'espèce, et permet
l'autogamie. Le rostellum modèle un prolongement en forme d'un crochet, la stipe (du
type hamalus). Au moyen de quatre caudicules minces, elastiques, les masses
polliniques sont reliées
à
la stipe. A la base du stipe se trouve le viscidium, qui ne
fonctionne qu' une tres courte periode, bien avant l'anthese.
Resumé
L'autofécondation, qui est la règle chez C.
trifida, est realisée par la dessication et
puis la monte du capuchon de l'anthere. Les masses polliniques tombent, bien unis aux
caudicules elastiques, vers la surface stigmatique, ou
ils restent collées.
The very high rate of fruit set is a clear indication for autogamy. According to
SUMMERHAYES (1951), 85-100 % of the flowers set fruit. CATLING (1983) held
the plants of C.
trifida in insect-proof cages, and found a autogamy-rate of 50
%. The
observations of FREUDENSTEIN (1992) also affirm the high degree of autogamy. He
found, that 50 % of the open flowers had self-pollinated. Only 6,8
%
of the open
flowers had their pollinia removed.
* * *
Although there are various descriptions of potential pollinators and of the degree of
autogamy, one looks in vain in European literature if one tries to find a clear
description of the way in which pollination or autogamy takes place. The studies of
FREUDENSTEIN (1992, 1994a, 1994b) have filled up this lack, but it was not until
after we completed our own observations, that we heard of his studies.
Previous studies
The genus
Corallorrhiza has its main area of distribution in northern and central
America, where we can find ten species. Only one species,
Corallorrhiza trifida, can
be found in Europe. It is widely spread from the arctic to the submeridional zone and
can rarely be found in the meridional zone BUTTLER (1986).
Morphology and function
The little, yellowish-green plant has no leaves, just some sheath-like scales. Its name
refers to the corralloid rhizome. C.
trifida was before often described as being
saprophyte. e.g. in HEUKELS (1911) and VERMEULEN (1958), but is in reality a
mycoparasite, because the plants don't get their nutrition directly from the organic
material, but "their interaction with fungi is facilitated by the coralloid rhizome"
FREUDENSTEIN (1994). The rootless rhizome is a typical feature of this species.
Let's first describe the morphology and function of the column of C. trifida. The
column is about 2.0-3.3 mm long, slightly curved forward, having a ventral shallow,
gutter-shaped central channel. The stigma is oblong-elliptic-cordate, lying in a cavity,
perpendicular to the column axis. The anther cap is fugacious, whitish-yellow when
fresh, later on turning brown FREUDENSTEIN (1992).
The different European authors do not agree about rostellum, pollinies and their
connection. CAMUS (1929): C.
trifida has a bilocular anther without appendage or
rostellum.
SCHLECHTER, in describing the subtribe of the
Corallorrhizinae: "Die Pollinien ....
sind immer wachsartig und von fester Konsistenz und kleben bei
Concerning the possible pollinators of C.
trifida, there can be found several
indications in literature. SILÈN (1906) observed the visit of several Syrphids and
other small insects. He suggested that, because the pollinies do not possess a
630
Journal Europäischer Orchideen 30(3): 1998. Journal Europäischer Orchideen 30(3): 1998.
631
pollinium and viscidium. In e.g. the genus
Orchis we can see two caudicles,
connected with one common viscidium. The caudicles are an extension of the pollinies
and may often be yellowish.
The rostellum in its turn can also form a connection with the caudicles, which is called
stipes. So the stipes is an extension of the rostellum, and consists of cellular tissue of
the rostellum. In our case, the different colour of stipe (whitish) and caudicles
(yellowish) is an indication for the different place of initiation of both structures,
although one cannot always be able to state that two structures are different in origin,
j
ust on the basis of colour and consistency (DRESSLER pers. comm.). Their different
origin can best be seen in anatomical sections, where it is clear that the stipes is
cellular, while the caudicles are essentially just a secretion (FREUDENSTEIN, pers.
comm.)
RASMUSSEN (1985, 1986) distinguishes two types of stipes. The tegula is a
connecting strap, consisting of an only several layers, derived from the dorsal
epidermis of the rostellum. A hamulus is the entire distal portion of the rostellum,
prolonged into a stalk (FREUDENSTEIN 1994). Because of its delicacy and its
p
osition the tegula is much more difficult to observe than a hamulus.
FREUDENSTEIN (1994a, 1 994b ) shows beautiful microscopic cuts that demonstrate
stipes of the tegula-type
(Calypso bulbosa), and of the hamulus-type
(Corallorrhiza). Here one can clearly see the hook-like shaped stipes.
manchen Gattungen mit ihren Spitzen zusammen, oder aber es ist eine deutliche
Kaudikularbildung zu sehen, die manchmal als eine viereckige Platte beschrieben
wurde. Jedenfalls handelt es sich offenbar dabei weder um einen Stipes noch um ein
Viscidium" SCHLECHTER (1970, pA08). A little further, when describing
C.
trifida,
he says: "Die vier Pollinien hangen zusammen, und manchmal wird ein kleines, etwa
viereckiges Kaudikulum gebildet" SCHLECHTER (1970, p. 412). Perhaps he meant
the four caudicles, when speaking about a four-edged "Kaudikulum".
ZIEGENSPECK (1936) doesn't mention caudicles or viscidium. He points out that,
j
udging by the construction of the flower, it should be well pollinated by insects.
However, autogamy seems to be the rule. After ZIEGENSPECK the pollinies fall
apart when growing older and then fall onto the stigmatic surface. This process is
facilitated by the fact that, when the pollinies des integrate, the column bends
forward.
VERMEULEN (1958) mentions a little, roundish rostellum and says nothing about the
connection with the four pollinia.
In more recent literature the authors agree about the composing elements of the
column, but do not give information about the functioning of those elements. LUER
(1975): "The column is compressed and the anther is terminal, with four yellow, waxy,
subspherical pollinia, all of which are connected by a single, microscopic, elastic band
to a detachable viscidium". The only element lacking in his description is the presence
of a stipes. REINHARD et al (1991):" ... die vier Pollinien hangen zusammen, das
Viscidium ist ablOsbar; der Stipes ist klein und schmal. Details des Saulenbaus sind
wenig erforscht".
DRESSLER (1993) classifies
Corallorrhiza in the tribe Calypsoeae, a tribe
characterized by four superposed pollinia, stipe and viscidium. DELFORGE (1994)
states that the pollinies are connected with the pollinia by means of an elastic
caudicle.
As soon as the anther cap opens, about one week before anthesis, one can observe the
p
osition of the four pollinia, superposed, with the members of a pair stacked, one on
top of the other (photo 2 + 3). They are lense-shaped and flattened on the side where
they are pressed together. The pollinia are separated by a very thin, horizontal layer
(the septum), which later in development desiccates, shrinks and then is hardly visi
b
le
any more. The pollinia form four very thin, elastic caudicles which, as soon as the
anther opens, contact the hook-like stipes.
Unlike SILEN (1906), we were able to remove the pollinaria of
C.
trifida with a
needle, although this was only possible for a short time, directly after pollinia and
viscidium, with the help of the stipes, were connected with each other (photo 4). In
FREUDENSTEIN (1994a, p. 5, ill. a) one can clearly see, that the viscidium is placed
at the basis of the stipes. So pollination is basically possible, but as far as we could
observe, the viscidium only functions with a newly opened anther, when the flower is
still closed. It seems that when growing older, the viscidium looses its adhesive power.
Observations
In studying
C.
trifida, we experienced, that it is very important to study the flowers in
the very early stages of development, that is to say long before anthesis. For several
years we studied the development of the column of
C.
trifida.
It proved, that the development of the rostellum is of crucial importance, since this
organ determines the way in which pollination can take place. In
C.
trifida the
rostellum develops a prolongation, the stipes (photo 1). The difference between
caudicles and stipe is the place where they are formed. The caudicles are made in the
anther and consist of elastoviscin (the elastic material which keeps united the
pollengrains) and pollengrains. Their function is to unite
In
C.
trifida auto-pollination usually takes place before or directly after anthesis. As
soon as the anther cap has opened and the pollinaria are connected with the stipes, the
anther cap lifts upward, dries out and very soon falls off. The pollinia
632
Journal Europäischer Orchideen 30(3): 1998.
633
Journal Europäischer Orchideen 30(3):1998.
CATLING,P.M. (1983): Autogamy in eastern Canadian Orchidaceae: a review of
current knowledge and some new observations.- Naturaliste Canadien 110:
37-53.
DAVlES,P
&
J and A.HUXLEY (1983): Wild orchids of Britain and Europe.-
London.
DELFORGE,P. (1984): Guide des Orchidées d'Europe, d'Afrique du Nord et du
Proche Orient.- Lausanne.
DRESSLER,R.L. (1993): Phylogeny and classification of the orchid family.-
Cambridge.
DRESSLER,R.L. (1961): The structure of the orchid flower.- Missouri Botanical
Garden Bulletin 49: 60-69.
FREUDENSTEIN,J.V. (1992): Systematics of Corallorrhiza and the
Corallorrhizinae (Orchidaceae).- PhD. dissertation, Cornell University.
Ithaca, NY.
FREUDENSTEIN,J.V. (1994a): Gynostemium structure and relationships of the
Corallorrhizinae (Orchidaceae: Epidendroideae).- Plant Systematics and
Evolution 193: 1-19.
FREUDENSTEIN,J.V. (1994b): Character transformation and relationships in
Corallorrhiza (Orchidaceae: Epidendroideae). 11. Morphological variation
and phylogenetic analysis.- American Journal of Botany 81(11): 14581467.
HEUKELS,H. (1911): De flora van Nederland. Deel 1, Orchidaceae.- Leiden/
Groningen.
KIRCHNER,O. (1922): Zur Selbstbestäubung der Orchidaceen.- Ber. Deutsch.
Bot. Ges.
40: 317-321.
LANG,D. (1989): A guide to the wild Orchids of Great Britain and Ireland.-
Oxford, New York.
LUER,C.A. (1975): The native orchids of the United States and Canada,
excluding Florida.- New York.
RASMUSSEN, F.N. (1985): Orchids.- In: DAHLGREN,RM.T. et al: The
families of the Monocotyledons - Structure, evolution and taxonomy.-
Berlin, Heidelberg, New York, Tokio.
RASMUSSEN,F.N. (1986): On the various contrivances by which pollinia are
attached to viscidia.- Lindleyana 1: 21-32.
REINHARD,H.R et al. (1991): Die Orchideen der Schweiz und angrenzender
Gebiete.- Egg.
SCHLECHTER,R (1970): Die Orchideen, 3.Auflage.- Berlin und Hamburg.
SILEN,F. (1906): Blombiologiska iagttagelser i sodra Finland. Medd. Soc. pro
Fauna e Flora Fennica, Bd. XXXII, 120-134.
SUMMERHAYES,V.S. (1951): Wild Orchids of Britain.- London.
then lie quite loose in the clinandrium and the least vibration is sufficient to make
them fall down to the stigmatic surface (photo 5). In this process the elastic
caudicles play an important role: because of their elasticity they easily allow the
p
ollinia to fall down. They have exactly the right size to make the pollinia land on
the stigma. So on one hand they give the pollinia a great freedom of movement,
but on the other hand they guarantee, that the pollinia will sooner or later fall onto
the stigmatic surface. In BAUMANN & KÜNKELE (1982, p.51) the illustration
shows very well, how the pollinia have fallen down and are already partly
sticking onto the stigma.
FREUDENSTEIN (1994b) reports that "C. trifida rotates its stipe with attached
pollinia to contact the stigma very soon after anthesis". During our observations
we didn't observe this phenomenon. In the plants we observed, the stipes kept its
place, and the contact between pollinia and stigma was achieved only by means
of the elastic caudicles.
Soon after making contact with the stigma, the pollinia are soaked with stigmatic
fluid. This can very well be observed by the colour of the pollinia: they become
more whitish and more or less melt together with the stigmatic surface.
We often observed that at the same time the stipes more or less disappeared, as i
f
b
eing dissolved from the stigmatic fluid. What's left is just a little, roundish
structure, just as VERMEULEN (1958) described it. He probably saw
C.
trifida
only in late stages of its development.
Acknowledgements
We sincerely wish to thank Dr. Robert L. Dressler, Dr. John V. Freudenstein, Dr.
Finn N. Rasmussen, Hans R Reinhard and Jürgen Reinhardt for their great help,
references to literature as well as for their constructive remarks. We also thank
Dr. Eckhard Willing and Henk ten Brinke for their help in providing literature.
Bibliography
BAUMANN, H & S. KÜNKELE (1982): Die wildwachsenden Orchideen
Europas. Stuttgart.
BUTTLER, K.P. (1986): Orchideen.- Munchen.
CAMUS, E.G & A. (1921-1929): Iconographie des Orchidees d'Europe et du
bassin méditerranéen.- Paris.
Journal Europäischer Orchideen 30(3): 1998.
Journal Europäischer Orchideen 30(3): 1998.
634
VERMEULEN,P. (1958): Flora Neerlandica 1/5, Orchidaceae. Koninklijke
nederlandse Botanische Vereniging.
ZIEGENSPECK,H. (1936): Orchidaceae. In: KlRCHNER,O.VON et al: Lebens-
geschichte del Bliitenpflanzen Mitteleuropas, Band 1.- Stuttgatt.
•
Authors' addresses
Jacques Kleynen
Pr. Constantijnlaan 6
N
L - 6241 GH Bunde
Jean Claessens
Moorveldsberg 33
N
L - 6243 AW Geulle
Figures (phot. pag. 637, photos by Jean Claessens and Jacques Kleynen)
2
C.
trifida:
column in very early state of development,
before
anthesis (flower opened manually).
photo I:
C.
trifida:
front view of a column with newly opened anther. Stipes
and caudicles well visible.
photo 2:
photo 3:
C.
trifida:
column side view showing stipes,
caudicles and pollinia.
photo 4:
C. trifida: column with newly opened anther (before anthesis,
flower opened manually). Pollinaria removed with the help of
a
needle.
photo 5:
C. trifida: Older stage of the column. Anther cap lifted, pollinia
already partially sticking onto the stigmatic surface.
636
637
Journal Europäischer Orchideen 30(3); 1998.
Journal
Europäischer Orchideen 30(3):1998.
