Variation in cones

Simple vs compound strobili

A strobilus is just a terminal collection of sporophylls (modified leaves that bear sporangia).

A simple strobilus is just that: a set of leaf-like structures (sporophylls) that bear pollen sacs or a set of leaf-like structures (sporophylls) that bear ovules.

A compound strobilus is a more branched system. The structure that bears the sporangia (the pollen sacs or ovules) appears to be a modified branch that is in the axil of modified leaf (a bract). We use the term "cone scale" for the modified branch that bears the pollen sacs or ovules. The cone scale sits in the axil of the leaf-like structure we call a "cone bract" or just "bract".

Check your understanding:

In some taxa that have compound strobili, the bract is fused to the abaxial side of the cone scale. In other taxa, the bract is free (not fused).

Bract fused to cone scale — Bract fused to abaxial surface of a cone scale on the seed cone of a pine tree.

The pollen cone of a pine tree (below) is one example of a simple strobilus. It is simply an arrangement of sporophylls.

Longitudinal section of pollen cone — Longitudinal section of a pollen cone of pine. The microsporangia are the pollen sacs. In this case, the cone scales are simply modified leaves.

Sessile vs stalked pollen sacs

Pollen cone with stalked pollen sacs — Ephedra pollen cone with stalked pollen sacs

Some gymnosperms have sessile pollen sacs and others have stalked pollen sacs.

The pollen cones of pines have pollen sacs that are sessile on the abaxial side of each pollen cone scale. These cones are shown to the left and diagramed above.

Other gymnosperms have stalked pollen sacs. These bear a superficial resemblance to the stamens of angiosperms. The pollen sacs of Ephedra, shown to the right, are stalked. (You may also notice that the pollen cone of Ephedra is a compound strobilus, with bracts subtending the structure that bears the pollen sacs.

Cone scale variation (seed cones)

Some cone scales are peltate; others are not

Peltate scales (like peltate leaves) are shaped somewhat like a parasol, with a stalk that attaches to the lower surface rather than to the edge.

Seed cones with and without peltate scales. — Seed cone with peltate cone scales (Cupressus) and with cone scales that are not peltate (Thuja). [Drawings from Kerner von Marilaun, 1895]

Cone scales may have prickles or not

Here is a little terminology you will probably not need. However, these terms help explain variation in the distal part of the cone scale.

The swollen end of a cone scale is called the apophysis.
A protuberance on the apophysis is the umbo. The umbo generally has a lighter color than the rest of the cone scale.
The umbo may have a prickle - a sharply pointed extension.

These parts are shown below:

Cone scale anatomy with umbos and prickles — Cone scale anatomy, showing the apophysis, umbo, and one species with a prickle. [Drawing from www.pinetum.org]

Check your understanding:

Seed variation

Seeds of some species have wings; seeds of others do not. Many times seeds will have dispersed or animals will have eaten the seeds by the time you find a cone on the ground. It is often possible, however, to see characteristics of seeds and their wings in the "shadows" and depressions or indentations they leave behind on the cone scale.

Signs of seeds and seed wings left behind on cone scales. — Seeds usually leave indentations in cone scales that can be measured. Wings often leave images on the cone scale that appear as a slightly different color.

Gymnosperms