Acer rubrum, red maple, is a native deciduous medium sized tree that can grow quickly to about 70 ft. It is noted for its early spring red flowers and its red fall leaves. Red maple is common and can be found as a city tree to a forest tree to a swamp tree.
Acer rubrum, red maple, blooms in early spring - early April. This burst of red compact flower clusters can easily be seen on the bare tree tops and you know spring is coming!
The flowers are easily out a few weeks before the leaf buds show green.
In order to bloom so early, all the flower buds and also the leaf buds are formed the previous year while the tree is still photosynthesizing and has energy to form the buds.
These abundant early spring flowers provide important nectar and pollen for the emerging insects.
Red maple usually is dioecious meaning that it has two kinds of flowers: male (staminate) and female (pistillate) that grow on separate trees.
The flowers have both female-like and male-like structures but both are usually not functional. In male (staminate) flowers, the female pistil is reduced and nonfunctioning (pistillode). In female (pistillate) flowers, male stamen-like structures are present but not functioning (called staminodes).
Red maple has a complex gender system. Red maple is technically polygamo-dioecious meaning that a tree can have both bisexual and unisexual flowers. Sometimes there are bisexual flowers where both the male and female structures are functioning.
Studies have shown occasionally a few female flowers would appear on a male tree or a few male flowers on a female tree. When there are both female flowers and male flowers on a tree, they would be on different branches. Also found was that the functional gender of a few trees would change over the years.
The flower buds form on short lateral twigs. The outer parts are modified leaves called bud scales that protect the embryonic flowers as they overwinter. The bud scales are red with fuzzy pale edges. Inside of each bud are about 5 flowers that emerge in early spring before the leaves open. The flowers have 5 sepals and 5 petals that are red and look alike.
Male (staminate) flowers:
A cluster of red anthers of multiple flowers are just beginning to emerge from the bud scales. The fuzzy edges of the red bud scales can be seen.
Stamens growing longer as the flower emerges. Some of the anthers are already dehiscing (releasing pollen)
The flowers with sepals/petals emerging from the bud. Bud scales are red and the petal/sepals are deep red too.
There are about 5 flowers in a bud capsule and each flower has about 8 stamens. These mature flowers have lengthened flower stalks (pedicels) and anthers that are dehiscing (releasing pollen) yellow pollen.
The flowers have 5 petals and 5 sepals forming two circles around the flower, the petals are on the inner side. The male flowers are frequently yellowish especially when they are mature.
A large cluster of mature male flowers.
There is a nectar disk at the base of both the male and female flower. Here, in the male flower, drops of nectar can be seen between the stamens. In a female flower, the nectar drops would be at the base of the ovary.
Female (pistillate) flowers:
Cluster of female flowers: red flower bud scales with pale hairy edge, multiple flowers on long pedicels (flower stalks) from a single bud, deep red 5 sepals and 5 petals, and a long bifurcated stigma from each flower.
In photo below:
white arrow: female structure - stigma,
yellow arrow: male-like structure - anther-like.
Is this anther like structure a staminode (nonfunctioning) or a stamen? At a minimum, at some time the anther like structure should release pollen if it is functional for the flower to be bisexual. Most likely in this case, the structure is a staminode and the flower is female.
The fruits develop from the female flowers in late April before the leaves are fully developed. The fruit is a samara which has wings and does not open when dried to release seeds. They were called “helicopters” because how they twirl as they float down. The clusters of samaras droop on long slender stems and ripen in late spring, early summer. These in the photo are redder than most. Some are almost entirely green.
Leaves: Red maple leaves are opposite and simple with 3 to 5 lobes. It has 5 distinct palmate veins that radiate from the stalk to each of the lobes. The two basal lobes are small or not present at all. The leaf margins on the lobes are roughly toothed. The leaves are about 5 inches long. In the fall the leaves turn to shades of red with splashes of yellow and green.
"How beautiful when a whole [red maple] tree is like one great scarlet fruit full of ripe juices, every leaf, from lowest limb to topmost spire, all aglow, especially when you look toward the sun! What more remarkable object can there be in the landscape?"
Plant & Habitat
The Acer rubrum tree forms a single trunk up to about 70 ft.
Red maple is one of the most abundant trees in the east. It grows in a wide range of conditions, soil, water, light, etc. It grows well in disturbed areas. It grows rapidly in the beginning. Its stump sprouts readily.
Red maple in urban setting: Chester, NJ
Red maple on small mounds in swamp: Great Swamp, NJ
Text by Millie Ling and all photos by Hubert & Millie Ling. Photos: NJ
Additional information / References
Additional information / references:
- USDA – Acer rubrum plant guide: polygamo-dioecious https://plants.usda.gov/DocumentLibrary/plantguide/pdf/pg_acru.pdf
- Gender Variation in a Red Maple Population (Acer rubrum; Aceraceae): A Seven-Year Study of a "Polygamodioecious" Species: abstract https://www.jstor.org/stable/2444057
- USDA Forest Service: Lots of info on habitat and life history. https://www.srs.fs.usda.gov/pubs/misc/ag_654/volume_2/acer/rubrum.htm
- Phytoimages - image of male flower - nectary & pistillode: http://phytoimages.siu.edu/imgs/paraman1/r/Aceraceae_Acer_rubrum_66093.html
- The USDA website shows Acer rubrum county distribution NJ as well in the US and other information: https://plants.usda.gov/home/plantProfile?symbol=ACRU