What Is a Strobilus? Spore Cones on Horsetails and Club Mosses
A strobilus is a cluster of spore bearing leaves at the end of a shoot. Horsetails plus some club mosses carry them.
The short answer
The UW Botany lab manual says spores form in sporangia on leaves called sporophylls. A cluster of sporophylls at the tip of a shoot is a strobilus. NC State says field horsetail bears spores on a light brown cone at the tip of a stem in spring. The plural is strobili.
What is a strobilus?
The UW Botany manual says spores form in sporangia borne on sporophylls. A cluster of sporophylls at a shoot tip forms a strobilus. In Selaginella both large plus small spore leaves sit in the same strobilus.
| Option | What it does | Source |
|---|---|---|
| Sporophyll | Spore bearing leaf | Introduction to vascular plants: the lycophytes (Botany 130) |
| Sporangium | Holds spores | Introduction to vascular plants: the lycophytes (Botany 130) |
| Strobilus | Tip cluster | Introduction to vascular plants: the lycophytes (Botany 130) |
How do horsetail strobili form?
NC State says field horsetail grows spores on a cone at the tip of a non green stem in early to mid spring. Green sterile stems follow. Iowa State says the fertile shoots are short lived. They stand 6 to 12 inches tall under a spore cone.
Fertile shoot: spring cone. Light brown cone: tip of stem. Sterile shoot: green after.
Where else do strobili appear?
The UW Botany manual says to look for strobili on club mosses. One lab club moss has sporophylls but no strobilus. Iowa State says each scouring rush stem is topped by a spore cone. Utah State says gymnosperms bear seeds usually on scales of a cone.
Club mosses: some form strobili. Scouring rush: cone on each stem. Conifers: seeds on cone scales.
Troubleshooting
Cone but no green? Fertile horsetail shoots lack green per NC State.
Seeds or spores? Horsetails bear spores per NC State.
Many tips with cones? Scouring rush tops each stem per Iowa State.
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Sources
- Introduction to vascular plants: the lycophytes (Botany 130), University of Wisconsin Botany
- Equisetum arvense (field horsetail), NC State Extension Gardener Plant Toolbox
- Equisetum: biology and management, Iowa State University Extension, Integrated Crop Management
- Tree and botanical glossary, Utah State University Extension Forestry
FAQ
What is a sporophyll?
The UW Botany manual says sporophylls are leaves that bear sporangia where spores form.
What is the plural of strobilus?
Strobili. The UW Botany manual uses strobili for more than one.
Do horsetails make seeds?
No. NC State says field horsetail reproduces by spores from a cone at the stem tip.
When do horsetail cones appear?
NC State says early to mid spring. Iowa State says the fertile shoots are short lived.
Does scouring rush have a cone?
Yes. Iowa State says each scouring rush stem is topped by a spore producing cone.
