HOW DENSE CAN YOU BE? MEASURES OF VEIN DENSITY IN ANGIOSPERM LEAVES

Recent explorations of hydraulic efficiency as an evolutionary constraint have identified vein density as a variable that has played an important role in plant evolution, particularly during the rise of the angiosperms. The metric most commonly used for comparing leaves with different vein densities is increasingly described as 'Vein Length per Area' (VLA), and has units of millimeters (of vein length) per square millimeters (of leaf surface area). The measurement of this requires both digital image processing and greater or lesser amounts human input, depending on methodology, and the practice of making such measurements seems to have arisen organically without extensive meta-analysis discussion. Here, I suggest three alternative ways of measuring vein density using a distance map, a sizing transform, and areole area distributions; then I compare these with vein length per area as it is typically measured; and finally I explore the measurement of vein density critically, treating it as a case study in accurate and meaningful digital data capture.