In the depths of winter, time feels endless. There will always be another weekend to haul cross-country skis from the closet. There will always be more evenings to hunker down with the ever-growing stack of bedside books. But then, suddenly, spring happens, and those best-laid plans vanish with the snowmelt. Temperatures bounce and runners emerge wearing shorts. At the Arboretum, willows (Salix) have leapt into action near the Hunnewell Building, their branches shifting to warmer yellows, dotted with swelling buds. Alders (Alnus) and hazelnuts (Corylus) have awoken, too, their catkins drooping ever-so low, and some conifers (like Metasequoia) have gotten right to business, producing clouds of pollen when you shake their cones.
Perhaps no flowers capture my mood better than those of the Persian ironwood (Parrotia persica). In winter, the buds are covered with dark velveteen scales, somewhat resembling the writer Edward Gorey, wearing one of his thick fur coats. But in spring, the coat is shed, and vibrant red stamens emerge. The flowers are small, but observing them up close reminds me of leaving the house in early spring, layered with a coat and scarf, and realizing, in mid-afternoon, that I am far overdressed. Others are out in in light jackets (or none), chatting with neighbors and tossing Frisbees. The flowers of Persian ironwood seem to suggest that everyone—myself included—should drop layers and follow suit.
Certainly, our most striking specimen of Persian ironwood is our oldest (accession 2230*A), which is tucked behind the hickories along Centre Street. This tree, accessioned in 1881, now comprises five burly trunks, along with a low thicket of upstarts. When I took classes on plant identification as an undergraduate, I learned Persian ironwood as a large bush or small tree, but this specimen proves that a “small tree” can be something quite substantial. The largest trunk has a circumference, at breast height, that I cannot wrap my arms around. The stems twist with sinewy ripples, as though flexing, and the bark—ah, the bark—flakes away in small splotches. When the International Dendrology Society named Persian ironwood the tree of the year in 2007, they listed this accession as the tallest known representative of the species, rising to more than 69 feet (21.1 meters) tall.
This Persian ironwood came to the Arboretum from the Harvard Botanic Garden, which then occupied seven acres on Garden Street, not far from Harvard Square in Cambridge. The garden had been established in 1807, and when Asa Gray was appointed a professor of natural history at Harvard in 1842, he simultaneously took over the garden. In fact, Gray lived in a stately home overlooking the collection, and his herbarium was situated next door. Then, in 1873, Charles Sprague Sargent assumed the directorship of the Harvard Botanic Garden, at the same time he officially became the first director of the Arboretum. Sargent aimed to expand and regroup the garden, rearranging the plantings to mirror the taxonomic system that Gray used to organize the herbarium. Sargent would later adopt this same idea for the Arboretum. “It is hoped,” Sargent explained to the Boston parks commissioners in 1879, “that such an arrangement, while avoiding the stiff and formal lines of the conventional botanic garden, will facilitate the comprehensive study of the collections, both in their scientific and picturesque aspects.”
Incidentally, the Persian ironwood, as a member of the witch-hazel family (Hamamelidaceae), falls outside of this taxonomic arrangement, as do numerous other small trees and shrubs planted nearby. This break from the plan can be explained, at least partially, by this location providing a protected microclimate within the Arboretum—a space where winter temperatures are somewhat buffered. While Persian ironwood is quite hardy (even surviving in southern Minnesota), other neighboring members of the family, like several species of winter-hazel (Corylopsis), are more sensitive to the cold, or at least their flowers are. When Sargent wrote about winter-hazels in 1916, he noted, in exasperation that the flowers were regularly “destroyed,” due to late frosts. This year, if all goes well, yellow flowers will soon festoon our winter-hazels, but for now they are holding back, letting the Persian ironwood shed its winter coat and test the prospects of spring.