The Arnold Arboretum of Harvard University

The Arboretum for Educators

Resources for Teachers, Students, and Families
 
December 2025
During the 2025–2026 school year the Arboretum for Educators will feature one native tree species per month, highlighting recognizable features and sharing interesting facts. This will be followed by Outdoor Journaling suggestions and related Science Labs. Embark on a yearlong tree investigation and outdoor journaling program: can you “collect” all 10 trees by June? Be sure to read the previous newsletters.

Festive Hollies

iIex opaca
A cheery red berry against a dark green leaf brightens the spirit as we approach the winter solstice! Since ancient times the holly genus (Ilex) has been imbued with significance and hope by humans across the world, and appreciated by wildlife as a source of food and shelter during cold winter months. In North America, there are 23 native species, many found as far south as Florida, far west as Texas and all along the eastern seaboard to Massachusetts. Hollies exist as separate male and female plants—dioecious—so it is important to plant both in order to enjoy the characteristic red fruit. Get to know three specific hollies this December!
Ilex opaca branch
American holly (Ilex opaca) evergreen leaves are rather thick, glossy, dark green and sharp to the touch due to the spines along the leaf margins and tips. The leaves are arranged alternately on the branches. The poisonous (to humans and pets) round berries grow in clusters along the stem and persist throughout the winter. The entire holly tree can grow to 50 feet tall and maintains a dense, pyramidal shape. It is quite a specimen!
Ilex glabra branch
Inkberry holly (Ilex glabra) is another evergreen species, but this one grows as a shrub only up to 8 feet tall. The leaves are also glossy and rather thick, though medium green on top and slightly duller green underneath. The margins are mostly smooth with a few fine teeth closer to the tips. The berries are small, shiny black (hence the name inkberry!) and dangle individually on short stalks from the stems. Historically, soldiers crushed the berries to make black ink for writing letters while Indigenous peoples thickened the juice with acorn flour to make paint.
Ilex verticillata branch
Winterberry holly (Ilex verticillata) is easy to spot in winter as it is a deciduous holly and its most appealing feature—red berries—covers every inch of this 5-15ft. tall and wide shrub. Winterberry is most often used in holiday floral arrangements! If you were to spot the green leaves, you would notice they are papery thin with serrated margins and prominently visible veins on the surface; the underside is covered in short fine hairs. Clearly these leaves are not adapted for winter conditions compared with the two species above. Winterberry grows best in moist soil conditions and full sun.
Ilex verticillata in winter
Outdoor Journal Activities
  1. Locate some evergreen hollies and carefully touch the leaves. Note the thickness, smooth surface texture and glossy shine. Are the leaves straight or slightly curved? What happens if you place a few drops of water on the leaf? Why do you think that happens? Can you feel the veins? How is the underside different from the topside?
  2. Trace some holly leaves and measure their dimensions. Count how many spines on a leaf. Do all leaves of the same tree have the same number of spines? Look for leaves from different parts of the tree. Write down all your observations!
  3. Squeeze some berries and count the seeds inside. Smell. What does it remind you of? Can you observe any birds nearby feeding on the fruits? Make sure NOT to eat any berries yourself! Note how the berries grow on the branches and record all your observations in your journal.
  4. Can you find a male holly tree? How can you tell that it is male? How far away are the female holly trees?
  5. Find more outdoor ideas for engaging with hollies.
Science Labs
  1. Use hollies to understand winter plant adaptations and defenses against herbivory. Watch this video to set up a field lab lesson. Students will gather and interpret data and use it to form hypotheses. If you have different holly species, compare results among them to continue hypothesizing.
  2. Thick evergreen holly leaves are perfect for learning about stomata! Teach your students how to do stomatal peels using nail varnish or even white school glue! Once they are experts at obtaining good peels and using microscopes, practice gathering data across a variety of evergreen leaves and indoor house plants. This could be launching point to discuss how carbon affects plant physiology or generate science fair topics!
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