Horticulture agents periodically receive inquires from homeowners about the plants, insects, and disease problems that come from their home garden. Sometimes the questions include a photo of a plant and other times a sample is collected and brought to our office.
The samples that really try us are the ones that include no roots, stems, flowers, or buds, just a single leaf. Sometimes not even the whole leaf is included, just one leaflet from the entire leaf. The more information we receive, the easier it is to narrow down the possibilities, though many times, through sheer love (or hate) of the plant we can identify it by just one leaf.
Recently, an individual came to me with just such an inquiry. Over the phone, I initially received a call with the question that sounded something like, “There’s this tree in my yard, it just showed up, it has huge leaves and within a few weeks it is now 10 feet tall. The leaves are enormous and round, what kind of plant is this?” My gut told me it was an empress tree (Paulownia tomentosa). It has giant leaves and can grow that tall in the first year. However, the shape of the leaf can vary. So I asked the individual to either send me a photo or bring a sample to the office.
Identifying a plant takes me back to those games I played when I was a kid. You know the “guess who” game that involves narrowing down your opponent’s person by focusing on their differences.
When identifying a plant based on its leaves, you look for the characteristics that set it apart and make it unique. The size and shape of the leaves is one element. Is the leaf hairy (pubescent)? Is the leaf margin serrated, lobed, or entire? What color is the petiole (the stalk attaching the leaf to the stem)? Is it a single or compound leaf?
Surprisingly the hardest plants for me to identify are the ones that have the simplest leaves. I have to remind myself, that what makes that plant unique is how absolutely plain the leaves are. A good example of this is blackgum (Nyssa sylvatica).
The individual did bring me a sample of one leaf. Right away I did recognize it as the empress tree (Paulownia tomentosa). It was about 10 inches long and wide with three lobes and very pubescent. This particular tree has different leaves when it is in its juvenile phase. As the tree matures the leaves become more heart shaped.
It is not uncommon for several plant species to have juvenile leaves that change as the plant matures. Another characteristic that can stump even the best is some plant species have several different plant leaves on the same plant. Mulberry (Morus alba) and sassafras (Sassafras albidum) are good examples of this. This is why it is helpful to bring more than one leaf in for identification.
This fall as leaves change color, you who want to try identifying your trees on your own can use the free app called Leafsnap (leafsnap.com) that is free for iPhones and iPads. An online option is arborday.org/trees/whattree.
Still need help? Contact your local extension master gardener volunteer office by phone or by email. The Durham County Extension Master Gardener volunteers can be reached at firstname.lastname@example.org or at 919-560-0528.
Michelle Wallace is the Consumer Horticulture Agent for the NC Cooperative Extension Service in Durham County.