Strobili

A strobilus (plural: strobili) is a structure present on many land plant species consisting of sporangia-bearing structures densely aggregated along a stem. Strobili are often called cones, but many botanists restrict the use of the term cone to the woody seed strobili of conifers. Strobili are characterized by a central axis (anatomically a stem) surrounded by spirally arranged or decussate structures that may be modified leaves or modified stems.

Leaves that bear sporangia are called sporophylls, while sporangia-bearing stems are called sporangiophores.

Some members of both of the two modern classes of Lycopodiophyta (Lycopodiopsida and Isoetopsida) produce strobili. In all cases, the lateral organs of the strobilus are microphylls, bearing sporangia. In other lycophytes, ordinary foliage leaves can act as sporophylls, and there are no organized strobili.

Strobili of Lycopodium

Liquid-preserved strobili of Lycopodium, showing reniform sporangia through translucent sporophylls

Strobili of Selaginella

Liquid-preserved strobili of Selaginella, showing mega- and microsporangia through translucent sporophylls.

The single extant genus of Equisetophyta, Equisetum, produces strobili in which the lateral organs are sporangiophores. Developmental evidence and comparison with fossil members of the group show that the sporangiophores are reduced stems, rather than leaves. Sporangia are terminal.

Strobilus of Equisetum

Liquid-preserved strobilus of Equisetum, showing sporangiophores

Cross-section of liquid-preserved strobilus of Equisetum, showing sporangiophores bearing sporangia

With the exception of flowering plants, seed plants produce ovules and pollen in different structures. Strobili bearing microsporangia are called microsporangiate strobili or pollen cones, and those bearing ovules are megasporangiate strobili or seed cones (or ovulate cones).

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Wikipedia