Colorful Cross Sections

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Identification of trees and shrubs may involve cutting through a twig or branch and inspecting the cut surface. For many species, the color of the pith can be an interesting and helpful feature in the ID process.
Four examples are provided in the first image. Clockwise from top left, the yellow cross-section of Mahonia sp.; the salmon-pink pith of Kentucky coffeetree (Gymnocladus dioicus); the small greenish pith of osage-orange (Maclura pomifera); and the chalky-white pith of Euscaphis japonicus.
Image of four cross sections
But another look is needed for the osage-orange, as the appearance of the pith can vary. The second image shows stem cross sections from the same plant, with a more distinctive pith resembling the salmon-pink color of the Kentucky coffeetree. The milky sap associated with this species is also very noticeable in the second image. The spines, by the way, are sharp and stout.
Image of osage-orange cross sections
For a comprehensive approach to winter twig ID, be sure to visit Winter Twig Keys, developed by Jon M. Stucky and Alexander Krings.