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The veins that irrigate leaves during photosynthesis are demonstrated to be strikingly more abundant in flowering plants than in any other vascular plant lineage. Angiosperm vein densities average 8 mm of vein per mm2 of leaf area and can reach 25 mm mmK2, whereas such high densities are absent from all other plants, living or extinct. Leaves of non-angiosperms have consistently averaged close to 2 mm mmK2 throughout 380 million years of evolution despite a complex history that has involved four or more independent origins of laminate leaves with many veins and dramatic changes in climate and atmospheric composition. We further demonstrate that the high leaf vein densities unique to the angiosperms enable unparalleled transpiration rates, extending previous work indicating a strong correlation between vein density and assimilation rates. Because vein density is directly measurable in fossils, these correlations provide new access to the physiology of extinct plants and how they may have impacted their environments. First, the high assimilation rates currently confined to the angiosperms among living plants are likely to have been unique throughout evolutionary history. Second, the transpiration-driven recycling of water that is important for bolstering precipitation in modern tropical rainforests might have been significantly less in a world before the angiosperms.

Item Type:	Refereed Article
Keywords:	venation; transpiration; assimilation; tropical rainforest; tracheophyte
Research Division:	Biological Sciences
Research Group:	Evolutionary biology
Research Field:	Biological adaptation
Objective Division:	Environmental Management
Objective Group:	Terrestrial systems and management
Objective Field:	Terrestrial biodiversity
UTAS Author:	Brodribb, TJ (Professor Tim Brodribb)
ID Code:	62064
Year Published:	2009
Web of Science® Times Cited:	279
Deposited By:	Plant Science
Deposited On:	2010-03-09
Last Modified:	2010-05-10
Downloads:	0