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Growth of Lichens on Palm Trees
by: Prof. Isidro T. Savillo
Savillo, I. 2003. Growth of Lichens on Palm Trees at http://www.oocities.org/growth_lichens/index.htm or at http://www.biologybrowser.org/bb/Geography/Asia/Philippines/index.shtml or at http://www.biologybrowser.org/bb/Organism/Plantae/Lichenes/
Click here for the ABSTRACT
Palm trees in the Philippines would only harbor lichen growth when the physical and chemical conditions are ambient, there is availability of propagules in the vicinity and the trees have reached a certain age as shown by the presence of circular dents or scars and/or deposition of secondary growth leading to non chlorophyllous stems. Areca catechu was the most common palm whose trunk was sometimes almost completely covered by a mixture of spreading corticolous lichens. Other palm trees such as Corypha elata and Vecchia merrillis also manifested moderately luxuriant lichen growth. As observed, Palm trees would favorably allow the growth of corticolous lichen even in places where there were moderate to constant exposure of vehicular pollution but these lichen types did not or scarcely grew on neighboring woody trees. Moreover, these corticolous lichens could spread luxuriantly on palm trees during continous rain even when they were located in area accessible to vehicular pollution such as those growing besides the roads or busy park. The phenomenon wherein palm trees harbored corticolous lichens in an extra- ordinary manner compared to other woody trees in the same vicinity was preliminary analyzed.
The development of propagules usually in soredial form, was most likely observed to start appearing on circular dents or scars carved on the surface of the palm tree trunk. These were seen on palm trees whose outermost trunk retained the chlorophyllous character thus allowing only the growth and development of propagules on the circular dents or scars which were non chlorophyllous, rough and not fibrously slippery. These propagules would then grow by spreading outwards towards the chlorophyllous portion. Their ability to adhere tightly to the green portion of the trunk had continuously satisfied their crustose or foliose nature despite of the fibrously slippery texture of the substrate. In case of palm trees where the older portions of the stems had developed secondary growth, propagule development started on some rough and/or minutely cracked areas of the trunk such as in Cocos nucifera, Corypha elata and other palm trees with elongated trunks. The slim trunks of Areca catechu harbored lichen growth luxuriantly covering almost the whole trunk. This was followed by Corypha elata and Vecchia merrillis where the lichen grew continuously spanning more than the vertical half of the trunk. On the other hand, Cocos nucifera did not posses the same luxuriant population growth of lichens as that of Corypha, Areca and Vecchia. Lichens were observed to grow on one side of the Cocos nucifera where water flowed from the base of the modified leaves. The unequal distribution of trunk wetting was mainly attributed to the curving or slanting position of some Cocos nucifera as it aged and grew considerably taller. The lichen growth was non- continous and appeared as sporadic bursts.
Most lichens remained alive during the dry season on palm trees but not as healthy as during the rainy season. Dry season in the Philippines was characterized by the arrival of surprising rains brought about by the tropical convergent zones. There might be more water saturation on the trunks of palm trees brought about by the bases of the modified leaves which served as temporary reservoir of rain water and the “husky” nature of the outer internal structure of its trunk. Death to a few lichens on palm trees usually occurred when they were located in areas prone to vehicular exhausts and this usually happened during dry season. When there was continous rain, the Corypha elata displayed the luxuriant growth despite of its location which was near the busy highway.
In open seas, the Cocos nucifera were observed not to harbor lichen growth. On the other hand, Terminalia catappa harbored lichen growth on area of the trunk facing away from the sea. However in bays or islands partly surrounded by islets, Cocos nucifera were seen to harbor lichen growth. The mountains which jutted out and served as barrier to the piece of ocean might have reduced the availability of the sea spray to the growing lichen.
Moreover, Cocos nucifera was observed to harbor more crustose lichens which were non sorediate and non isidiate. Their reproduction depended largely on the common presence of fertile thalli thus the availability of ascospores for the photobionts to associate. Luxuriance of lichen growth was based mostly on foliose lichens considering that the thalli of some crustoses are not as discernible as that of the folioses.
Taxonomy of Lichens Growing on Palm Trees
Lichens identified were seen on trunks or roots of palm trees encountered and this does not signify whether they are pollution tolerant or sensitive. This is just a list of lichens identified through inspection, living on palm trees.
Areca catechu- Dirinaria applanata (Fee) Awasthi, Pyxine cocoes (Swartz) Nyl, Physcia sp. (without the lower cortex) (Sipman, 2001. personal communication), Physcia sorediosa (Vain) Lynge and Graphis cf persicina Vainio; Vecchia merrilis- Physcia sp. (without the lower cortex) (Sipman, 2001), Graphina hiascens Mull Arg, Pyxine cocoes (Swartz) Nyl; Corypha elata- Physcia sorediosa (Vain) Lynge, Pyxine cocoes (Swartz) Nyl, Physma brysinum (Ach)Tuck, Coccocarpia glaucina Krempelh, Parmotrema sp. and Graphina mendax Mull Arg; Cocos nucifera- Dirinaria applanata (Fee) Awasthi, Physcia sp. (without the lower cortex), Lecanora sp., Pyxine cocoes (Swartz) Nyl, Amandinea efflorescens (Muell. Arg) Marbach, Pyrenula ochraceoflava (Nyl.) Harris, Arthonia cf antillarum Nyl., Dirinaria picta (Swartz) Clement and Shear, Graphina hiascens Mull Arg, Dirinaria papillulifera (Nyl) Awasthi and Pyxine consocians Vainio.
Acknowledgement
I sincerely thank Dr. Harrie Sipman for his assistance and guidance on the identification of the lichens.
References
1. Arvidsson, Lar. 1982. A monograph of the lichen genus Coccocarpia. Opera Botanica. No. 67.
2. Awasthi, D.D. 1975. A monograph of the lichen genus Dirinaria. Editor. J. Cramer, A.R. Gantner Verlag KG, FL- 4940 Valuz.
3. Awasthi, D.D. Pyxine in India. Phytomorphology 30, 359-379.
4. Louwhoff, S.H. J.J. and J.A. Elix. 1999. Parmotrema and allied lichen genera in Papua New Guinea. Editor: J. Cramer. Bibliotheca Lichenologica Band 73. Gebruder Borntraeger, D- 14129.
5. Moreberg, R. 1990. The lichen genus Physcia in Central and South America. Nord. J. Bot.- section Lichenology 10(3).
6. Thrower, S.L. 1988. Hongkong Lichens. Urban Council Publications, Hongkong.
7. Vainio, Edv. A. 1921. Lichenes Insularum Philippinarum III. Helsingforsiae. Sumptibus Academiae Scientiarum Fennicae.
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