Follicle

follicle [ FOL-i-kuhl ] noun: a dry, dehiscent fruit from a superior, unilocular (single cavity) ovary splitting along only one suture when mature

If you grow milkweed to attract monarch butterflies to your garden, then you know that they also attract milkweed bugs. You often find these bright red and black insects massed on the milkweed “pods” trying to gain access to the seeds within. But, do you know that the fruit of the milkweed is not actually a pod but rather a follicle?

Pods are technically legumes, which are similar to follicles as both develop from a superior, unilocular ovary. However, when a follicle matures and dries, it dehisces or splits along only one suture. A ripe legume, on the other hand, dehisces along both sutures from top to bottom.

Follicles of Asclepias incarnata with oleander aphids and milkweed bugs — Follicles of native *Asclepias incarnata* (swamp milkweed) in various stages of maturation covered with oleander aphids and milkweed bugs
in September. Photo © Mary Free

Follicle of mature native Asclepias syriaca (common milkweed) — Follicle of mature native *Asclepias syriaca* (common milkweed) covered with adult large milkweed bugs and nymph that eat the seeds, helping to regulate milkweed populations
in September.Photo © Mary Free

Follicles dehisce along only one suture as illustrated by Consolida ajacis (giant larkspur) — Follicles dehisce along only one suture as illustrated by these non-native *Consolida ajacis* (giant larkspur) fruit in July.
Photo © Elaine Mills

Legumes dehisce along two sutures from top to bottom as illustrated by Baptisia australis (Blue Wild Indigo) — Legumes dehisce along two sutures top to bottom like native *Baptisia australis* (blue wild indigo) fruit in October. Photo © Elaine Mills

Follicles can occur as simple fruits, derived from a single ovary in a flower. For example, a Paeonia (peony) fruit has five follicles, which develop from the five carpels in its single ovary. When follicles develop from multiple ovaries in a single flower, they are considered an aggregate fruit called an etaerio of follicles. The fruit of Aquilegia (columbine) also has five follicles, but they develop from five separate ovaries within the flower so are considered an aggregate fruit. Other examples include Helleborus (hellebore) and the cone-like aggregates of Magnolia.

Five dehsiced follicles of Paeonia mascula — Five dehsiced follicles of *Paeonia mascula* (wild peony) exposing black seeds and red unfertilized ovules.
Photo by Secundum naturam

Five follicles of native Aquilegia canadensis with seeds — An aggregate of five follicles of native *Aquilegia canadensis* (wild columbine) dehisced with seeds exposed in June.
Photo © Mary Free

Aggregates of follicles of Helleborus — Aggregates of follicles of *Helleborus* (hellebore) in varying stages of maturation, dehiscence, and disintegration. Photo © Mary Free

An aggregate of follicles of native Magnolia virginiana — An aggregate of follicles of native *Magnolia virginiana* (sweetbay magnolia) showing sutures where follicles will dehisce. Photo © Mary Free

Plants in the Apocynaceae (dogbane family) have two ovaries: in Amsonia (blue-star) and Apocynum (dogbane), the ovaries share a single style and usually produce paired follicles whereas it is more likely for Asclepias (milkweed) to produce one follicle rather than twins because both ovaries develop only in a small percentage of the flowers.

Dehsiced, paired follicles of native *Amsonia tabernaemontana* (eastern blue-star) in August.
Photo © Elaine Mills

Paired follicles of native *Apocynum cannabinum* (Indian hemp) in June.
Photo © Elaine Mills

Dehisced follicles of Asclepias incarnata exposing seeds — Dehisced follicles of native *Asclepias tuberosa* (butterfly-weed) releasing seeds in August.
Photo © Elaime Mills

References

Apocynum cannabinum published by: The Morton Arboretum. (accessed through Data Portal, https://swbiodiversity.org/seinet/taxa/index.php?taxon=3709&clid=3232 , June 11, 2021).

Armstrong WP. 2001. Fruit Identification Photos #3. Buttercup Family (Ranunculaceae). Wayne’s World: 9 May 2001. (accessed June 11, 2021).

McLaughlin SP. 1982. A Revision of the Southwestern Species of Amsonia (Apocynaceae). Annals of the Missouri Botanical Garden, 69(2): 336-350. doi: 10.2307/2398939.

Morse D. 1993. The Twinning of Follicles by Common Milkweed (Asclepias syriaca). The American Midland Naturalist, 130(1): 56-61. doi: 10.2307/2426274.

Twining, E. 1868. Illustrations of the Natural Orders of plants. Digitized by the Internet Archive in 2010. page 146.

Whittemore AT. Aquilegia. Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico [Online]. 21+ vols. New York and Oxford. Vol. 3. http://beta.floranorthamerica.org/Aquilegia. (accessed June 11, 2021).