Purple Dots: A Dive into the Washington Park Arboretum’s Interactive Map

a screenshot of the stylized map, showing many green dots and a few purple dots.
A screenshot of the Washington Park Arboretum Interactive Map

If you’ve spent any time looking through our interactive map of the Washington Park Arboretum, you’ve probably noticed those purple plant dots. While most of the dots denoting different plants in the collection are bright Kelly green, some of them are a festive light purple color. But why?

I stumbled on this question while trying to identify a tree that I had taken a picture of when I was wandering through the arboretum a couple weeks ago. I now know that it is a Japanese maple (Acer palmatum), but having very little background in plants, the map has been incredibly helpful as I try to learn more about what I am looking at. My tree just so happened to be one of those purple dots. I clicked over to the legend and found no answers there. I immediately began looking through other purple dots, searching for some common characteristics to connect all the plants. I started clicking on random green dots, seeing if anything that came up was common between those plants, but different from the purple plants. The records that include pictures? The plants that don’t have an accession year? Nothing was lining up.

My curiosity led me first to my colleague Sasha McGuire. As Sasha has been here more than just a few months, I thought she might know the answer. She was just as unsure, but suggested I reach out to Ray Larson, our Curator of Living Collections and the Otis Douglas Hyde Herbarium – he would probably know. Being acutely aware that it was a Friday afternoon, we took a break down to his office to ask about the confusing purple dots. His answer was simple: “Those are the curator’s favorites.”

It made perfect sense – no individual quality or information was connecting the variety of plants. The mystery was solved and I felt good, especially in knowing that one of the plants that stood out to me had done the same for the curator. But then I began to wonder why again. Why was that tree picked over its neighbors? What stood out to him about that tree, or any other favorite plant, that it was singled out? This time, I knew exactly who to ask to answer my question.

“Usually I pick the plants based on them having at least one outstanding or unusual ornamental characteristic,” Ray explained. “So this is compiled from my knowledge about the particular plant species or cultivar, its prominence in the collection (and ease of finding it), or something that makes it especially worth seeking out.” Ray also mentioned that many of these plants have more than one season when they’re particularly interesting. If there is only one season, though, then there needs to be something striking or unusual about their peak, like scent, form, or a long blooming season. In summary: “make sure you see this if you visit.”

Of course I had to ask about my Japanese maple that started these questions. Ray likes the tree “because it is especially prominent and has consistently good fall color and a nice form.” As far as I’m concerned, its early summer leaves look great against a bright blue sky. Now I’m looking forward to seeing what it looks like in the fall.

Fiery yellow leaves tipped with red against a bright blue sky
Looking up through the leaves of the Japanese maple, Acer palmatum, X-282-B

Another criteria that might mean a plant receives a coveted purple dot? “Maybe it is a particularly interesting form of an otherwise common plant in the gardens,” Ray adds. His example for this category is a pair of large bigleaf maples (Acer macrophyllum) found in the northwest portion of the Mountain Ashes (Sorbus) collection. “These have appealing forms, are large specimens easily seen along Arboretum Drive E and play off each other nicely.”

Ray also likes to make sure that there’s at least one favorite in a given area, but acknowledges that’s not necessarily the case yet. “There are many good plants still to highlight and I haven’t spent as much time in the south and west ends of the arboretum,” he admits. With a desk at the Center for Urban Horticulture, I don’t get over to the arboretum as much as I’d like, but I definitely know what plants I will be checking out during my next visit.