What Is a Caruncle? Small Growths Near the Seed Scar
A caruncle is a small outgrowth on a seed coat near the point where the seed was attached. The Missouri Botanical Garden glossary defines it as a fleshy, often hard outgrowth near the micropyle, the tiny pore at the seed tip. Castor bean seeds have a clear one.
The short answer
A caruncle is a little cap at one end of some seeds. University of Wisconsin Extension says each castor bean seed has a small spongy caruncle at one end that helps absorb water for germination. Castor bean is in the spurge family. It looks like an elaiosome, but its main job is water uptake.
Where is the caruncle on a seed?
It sits by the micropyle near the hilum scar. The Missouri Botanical Garden glossary places it there and compares it with the elaiosome and the aril. NC State and Colorado State GardenNotes describe the seed coat, embryo and food store under it. See those parts in cannabis seed anatomy.
Which plants have a caruncle?
Castor bean is the classic case. Wisconsin Extension says it is the only member of its genus and sits in the spurge family, Euphorbiaceae. NC State describes the mottled seeds as resembling a tick, which is where the name Ricinus comes from.
| Structure | What it is | Source |
|---|---|---|
| Caruncle | Spongy or hard outgrowth near the micropyle | Missouri Botanical Garden, Wisconsin |
| Elaiosome | Fatty food body that draws ants | Missouri Botanical Garden |
| Aril | Fleshy covering grown from the seed stalk | Missouri Botanical Garden |
What does a caruncle do?
Wisconsin Extension says it helps the castor bean absorb water at germination. Water enters, the seed swells and the radicle splits the coat. Seeds stay viable two to three years, the same source notes, so dry cool storage matters, as common cannabis seed storage mistakes explains.
Caruncle vs elaiosome
Both are seed coat growths. Ants value the elaiosome as food, while the caruncle is described mainly by its spot and texture. Insects and plants interact in many ways, and pollinator roles are covered in what roles do bees play in outdoor cannabis.
Leaves after the seed
Wisconsin Extension describes castor bean as an ornamental with oversized tropical looking leaves. The Kind Seed Co blog covers leaf structure in cannabis leaf anatomy.
Sources
- Castor bean, Ricinus communis, University of Wisconsin Extension Horticulture
- Ricinus communis (castor bean), NC State Extension Gardener Plant Toolbox
- Glossary A to H, Angiosperm Phylogeny Website, Missouri Botanical Garden
- Extension Gardener Handbook, chapter 3: botany, NC State Extension
- Botany (CMG GardenNotes 120), Colorado State University Extension
FAQ
What is a caruncle on a seed?
The Missouri Botanical Garden glossary defines it as a fleshy, often hard outgrowth near the micropyle of a seed.
What does the caruncle do on a castor bean?
Wisconsin Extension says the spongy caruncle helps absorb water for germination.
What family is castor bean in?
Wisconsin Extension places Ricinus communis in the spurge family, Euphorbiaceae.
Is a caruncle the same as an elaiosome?
No. The Missouri Botanical Garden glossary lists them as separate structures and compares them.
How long do castor bean seeds stay viable?
Wisconsin Extension says the seeds stay viable for two to three years.
