Preserving Extant Metasequoia Shoots for Herbaria

Abstract

Shoots and branches of Metasequoia have proven notoriously difficult to preserve in herbarium collections because of the abscission of the needles on drying. In the course of preparing an exhibit, the Yale Peabody Museum of Natural History's Division of Paleobotany successfully maintained a nearly ripe seed cone of Araucaria intact during the drying process by introducing glycerol into its tissues. Like Metasequoia, ripe araucarian cones also disintegrate within a few weeks of drying. We decided to try this same preservation method on fresh-cut branches of Metasequoia. In September 2004, three shoots from a mature Metasequoia tree on the Yale Peabody Museum grounds were immediately photographed, wrapped in dampened paper towels and refrigerated for three days. Afterward, the shoots were soaked in a solution of ethanol and deionized water (95:5) for five hours, then immersed in a solution of glycerol and deionized water (50:50) for 11 days and placed in a drying oven for three months at 30 °C. On removal from the oven, the shoots were allowed to cure at a temperature of 17 °C and a relative humidity of 9% for approximately three months. The shoots were then mounted on herbarium sheets as normal and accessioned into the Yale Peabody Museum herbarium. After nearly three years, the foliage sprays are still intact and show no signs of deterioration.