Evolution of pollinaria structure in cambodian orchids
We have studied the species from 25 orchids genera, takened in Elephants Chain of South West Cambodia in october 2003. On this little territory, we have found all known types of the pollinarium structure. Number of pollinia reduces from eight to lower number (six, four and two). There are two parallel trends of development. One which exists is the free pollinia, and other with the formation of complex pollinaria structure. We shall propound the possible liaisons between genera.
Nous avons étudié les espèces de 25 genres d’orchidées, récoltées dans les montagnes de la Chaîne des Eléphants du Sud-Ouest du Cambodge en octobre 2003. Sur ce petit territoire nous avons trouvé tous les types connus de la structure pollinaire. Le nombre des pollinies se réduit de 8 à un nombre inférieur (six, quatre et deux). Il existe deux voies parallèles de développement. Une, qui existe, ce sont les pollinies libres, et une autre avec la formation d’une structure pollinaire complexe. Nous supposerons les liaisons possibles entres les genres étudiés.
Poster on 18th WOC, 11-14 March 2005, Dijon, France
|Materials and Methods
Most of founded in Cambodia orchids were litophyte plants who grow in little crevices of the rock (65%); the 30% of orchids were epiphytes, and only few were terrestrial species (5%). The living collection was deposited in the greenhouse of Parisian Museum.
The flourished orchids, have been studed in SEM and were distincted in the present list:
The pollinia of these orchids have been analysed in scan electron microscope (SEM). The fresh flowers were used for getting the intact pollinaria. It has been dried in a thermostat at 25° C and after metallized by gold. Modern electron microscope has been added for any amelioration of older examination methods (Telepova-Texier, 1998). In our prospections we have seen very small flourishing orchids, the most of them being at the period of fructification. Then, we have studied the structure of orchid flowers in the greenhouse during the 2004 year.
|Results and discussion
Any final inventory of cambodian orchids has been made at this moment. If in 1934 the flora of South-West of Cambodia contained approximately 100 species (Gagnepain and Guillaumin, 1930) in 2000 year there were mentioned 164 species (Schuiteman and Vogel, 2000). In this work the special attention was made to male parts of hermaphrodite flowers: anther, pollinia, stipes, viscidium, pollen grains. There is an important diversity in pollinaria structure between genera and also someones between the species (Fig. 1-6). There are two parallel mechanisms of pollinia reduction from 8 to 6, 4, 2 (I and II). Sept of 25 studied genera (Agrostophyllum, Acantephypium, Arundina, Calanthe, Eria, Eriodes, Spathoglottis) have eight slender pollinia in two pairs by four each one (Fig. 6). All these species belong to the subfamily Epidendroideae. One genus (Acantephypium) has in pairs the asymmetrical pollinia: below they are round and overhead - elliptic.
I. The 8 symmetrical pollinia of Eria and Eriodes genera are not attached on the common viscidium. We suppose these Eriodeae species being at the origin of the groupe, having a transformation of pollinarium structure in more simple form – the free pollinia (first groupe). However, it is not the loss, but the fusion processes, which comes to appearance of four (Fig. 1, 3, 4) and even two pollinia (Fig. 2) in this groupe. The species of tribe Coelogine have four big superposed pollinia (each composed from two equal half) and four granular viscidium. The progressive species of Epidendroideae subfamily have the particularity to produce the pollinia free (Bulbophyllum and Dendrobium). On account of the gradual loss of granular viscidium structure, it occurs or four, or two pollinia in the same of that two genera.
II. The genera, as Agrostophyllum, Calanthe, Spathoglottis, have also 8, but asymmetrical pollinia. Here we seen the fall in fertility of pollen grains at the base of pollinia, and after the loss of them, and the appearance of new structure - the stipes. The single Appendicula genus of South-West Asian has exeptionally six pollinia (Fig. 5); this is a result of the loss of one pollinia in each pair.
The distinctive character of the Vandoideae subfamily is a stipes presence: between pollinia and viscidium (Seidenfaden, 1992), but there are some exeption (for exemple, in the tribe Cymbidieae. The Vandoideae subfamily have 4 tribes (Dressler, 1981) with the number of pollinia equal to four, two and one. The tribe Cymbidieae is diveded in two groupe: two or four pollinia. Acriopsis javanica has the four slender pollinia, thin long stipes and minute viscidium (Fig. 3). Cymbidium lowianum has two cleft pollinia and has not stipes. This type of pollinarium structure can be compared with the species of Maxillaria tribe. In contraste, all species of Maxillarieae are characterized by four big pollinia (laterally flattened). They have very expand viscidium, but minute broad stipes, wich can be absent. Only one species of Polystachyeae tribe is know from Cambodia (P. concreta), having very short stips and 4 pollinia (two pairs, each from two unequal semiglobular parts). The species of Vandeae tribe have a complex pollinaria structure (Fig. 1), all with two pairs of pollinia, having different form (cleft, split, porate or whole). They stipes are also various forms. The important viscidium is sometimes protected by small cap on the anther tip.
The reducing to lower number of pollinia is an indication of progressive evolution inside the orchid family. There are two parallel mechanisms of pollinia reduction (from 8 to 6, 4, 2): loss or fusion. The ecology of cambodian territory is of an incredible exuberance in the morphological forms and its trends of the development.
Prof. Dr. AVERIANOV Leonid V. (Herbarium, Komarov Botanical Institute, Saint-Petersburg)
Prof. Dr. VIDAL Jules E. (Herbarium, Muséum National d’Histoire Naturelle, Paris)
Dr. HUL Sovanmoly (Herbarium, Muséum National d’Histoire Naturelle, Paris)
YOK Lin (lecturer in Royal University of Phnom Phen, Cambodia)
IEM Rainsy (conductor and cambodgian interpreter, Cambodia)
HOR Sanara (engineer of Phnom Phen Agronomic School, Cambodia)
DAM (local mountain guide, Cambodgia)
LOPEZ Elizabeth (Orchid’s greenhouse , Muséum National d’Histoire Naturelle, Paris)
MASCARELL Gérard (engineer of Electron Microscope Services, Muséum National d’Histoire Naturelle, Paris)
Dr. REYFTMAN Jean-Philippe (Numérical Impression Services, Muséum National d’Histoire Naturelle, Paris)
Dressler, R. L. 1981. The Orchids. Cambridge, Massachusetts, London. 332 p.
Gagnepain, F. and Guillaumin, A. 1934. Orchidaceae and Apostasiaceae. In : H. Lecomte (ed.),. Flore Générale de l’Indochine, Volume 6. Mason et Cie., Paris. pp. 142-652.
Schuiteman, A. and de Vogel, E. F. 2000. Orchid genera of Thailand, Laos; Cambodia and Vietnam. Grafische Vormgeving Kanters, Sliedrecht, Leiden, The Netherlands. 118 p.
Seidenfaden, G. 1992. The Orchids of Indochina. Opera Botanica. 114: 1-502.
Telepova-Texier, M. 1998. General problems in investigation of chlorophyllian air-roots of epiphitic orchids (Orchidaceae). I. Morphology. Rev. Cytol. et Biol. Végét. - Bot. 21: 3-15.
Legends of figures 1-6
1 - Pollinaria of Aerides houlletiana Reichenb. f.
2 - Pollinaria of Dendrobium tropaeliflorum Hook. f
3 - Pollinaria of Acriopsis javanica Reinw. ex Blume
4 - Pollinaria of Bulbophyllum pumilo (Hook.) Spreng
5 - Pollinaria of Appendicula reflexa Blume
6 - Pollinaria of Eria bipunctata Lindl.
© 2005 Marpha TELEPOVA-TEXIER