AOBPreview originally published online on April 3, 2008
Annals of Botany 2008 101(9):1363-1377; doi:10.1093/aob/mcn046
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In Tropical Lowland Rain Forests Monocots have Tougher Leaves than Dicots, and Include a New Kind of Tough Leaf
1 Department of Anthropology, University of California, 1156 High St, Santa Cruz, CA 95064, USA
2 Plant Sciences Department, University of Cambridge, Downing Street, Cambridge CB2 3EA, UK
3 19 Cananga Close, Kamerunga, Qld 4870, Australia
4 Department of Anthropology, George Washington University, 2110 G Street, NW, Washington, DC 20052, USA
5 Commonwealth Scientific and Industrial Research Organization, Sustainable Ecosystems, Tropical Forest Research Centre, PO Box 780, Atherton, Queensland 4883, Australia
6 Department of Biological Sciences, University of Aarhus, Ny Munkegade 1540, DK-8000, Aarhus C, Denmark
7 Singapore Botanic Gardens, National Parks Board, 1 Cluny Road, Republic of Singapore 259569
* For correspondence. E-mail njdominy{at}ucsc.edu
Received: 17 September 2007 Returned for revision: 27 November 2007 Accepted: 25 February 2008 Published electronically: 3 April 2008
Background and Aims: There has been little previous work on the toughness of the laminae of monocots in tropical lowland rain forest (TLRF) despite the potential importance of greater toughness in inhibiting herbivory by invertebrates. Of 15 monocot families with >100 species in TLRF, eight have notably high densities of fibres in the lamina so that high values for toughness are expected.
Methods: In north-eastern Australia punch strength was determined with a penetrometer for both immature leaves (approx. 30 % final area on average) and fully expanded, fully toughened leaves. In Singapore and Panama, fracture toughness was determined with an automated scissors apparatus using fully toughened leaves only.
Key Results: In Australia punch strength was, on average, 7x greater in shade-tolerant monocots than in neighbouring dicots at the immature stage, and 3x greater at the mature stage. In Singapore, shade-tolerant monocots had, on average, 1·3x higher values for fracture toughness than neighbouring dicots. In Panama, both shade-tolerant and gap-demanding monocots were tested; they did not differ in fracture toughness. The monocots had markedly higher values than the dicots whether shade-tolerant or gap-demanding species were considered.
Conclusions: It is predicted that monocots will be found to experience lower rates of herbivory by invertebrates than dicots. The tough monocot leaves include both stiff leaves containing relatively little water at saturation (e.g. palms), and leaves which lack stiffness, are rich in water at saturation and roll readily during dry weather or even in bright sun around midday (e.g. gingers, heliconias and marants). Monocot leaves also show that it is possible for leaves to be notably tough throughout the expansion phase of development, something never recorded for dicots. The need to broaden the botanist's mental picture of a ‘tough leaf’ is emphasized.
Key words: Dicots, fracture toughness, herbivory, leaves, monocots, punch strength, tropical rain forest
Present address: Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AE, UK.
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  P. J. Grubb, R. V. Jackson, I. M. Barberis, J. N. Bee, D. A. Coomes, N. J. Dominy, M. A. S. De La Fuente, P. W. Lucas, D. J. Metcalfe, J.-C. Svenning, et al. Monocot Leaves are Eaten Less than Dicot Leaves in Tropical Lowland Rain Forests: Correlations with Toughness and Leaf Presentation Ann. Bot., June 1, 2008; 101(9): 1379 - 1389. [Abstract] [Full Text] [PDF]
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