From en.wikipedia.org:
[Sporangia-bearing reproductive structure in some land plants] [text=the body
of cestode s, called a strobila] A STROBILUS ([plural form]: 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 some 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 _sporangiophore s_.
** Lycophytes
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. <gallery> Diphasiastrum complanatum strobilus
(01).jpeg|Strobili of _Diphasiastrum_ Lycopodium saururus.JPG|Strobili of
_Lycopodium_ Lycopodium strobilus wm.jpg|Liquid-preserved strobili of
_Lycopodium_, showing reniform sporangia through translucent sporophylls
Lycopodium strobilus mosbo6.jpg|Micrograph of the strobilus of _Lycopodium_
sp., showing spores borne in sporangia Selaginella pilifera0.jpg|Strobili of
_Selaginella_ Selaginella strobilus wm.jpg|Liquid-preserved strobili of
_Selaginella_, showing mega- and microsporangia through translucent
sporophylls </gallery>
** Sphenophytes
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.
<gallery> Image:Equisetum_hyemale.jpg|Strobilus of _Equisetum_ Image:Equisetum
sylvaticum 240405.jpg|Strobilus of _Equisetum_ Image:Equisetum strobilus
wm.jpg|Liquid-preserved strobilus of _Equisetum_, showing sporangiophores
Image:Equisetum strobilus xs of wm showing sporangiophores.jpg|Cross-section
of liquid-preserved strobilus of _Equisetum_, showing sporangiophores bearing
sporangia </gallery>
** Seed plants
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_).
*** Cycads
Cycadophyta are typically dioecious (seed strobili and pollen strobili are
produced on separate plants). The lateral organs of seed strobili are
megasporophylls (modified leaves) that bear two to several marginal ovules.
Pollen strobili consist of microsporophylls, each of which may have dozens or
hundreds of abaxial microsporangia.
<gallery> Image:Dioon edule04.jpg|_Dioon edule_, seed cone Image:Cycas
circinalis - sago palm - desc-top of trunk.jpg|_Cycas circinalis_, pollen cone
Image:Cycas microsporangia.jpg|Abaxial surface of _Cycas revoluta_
microsporophyll, showing microsporangia </gallery>
*** Ginkgos
The single living member of the Ginkgophyta, _Ginkgo biloba_ produces pollen
strobili, but the ovules are typically borne in pairs at the end of a stem,
not in a strobilus. When there are more than a pair of ovules in _G.
biloba_, however, or when fossil taxa bearing large numbers of ovules are
examined, it is clear that the paired ovules in the extant species are a
highly reduced strobilus. <gallery> Image:Ginkgo biloba
Inflorescences.jpg|Pollen cones of _Ginkgo_ Image:Ginkgo pollen cone
wm.jpg|Pollen cone of _Ginkgo_, showing microsporophylls each with two
microsporangia </gallery> [Clear]
*** Conifers
[Conifer cone] Pollen strobili of Pinophyta are similar to those of cycads
(although much smaller) and Ginkgoes in that they are composed of
microsporophylls with microsporangia on the abaxial surface. Seed cones of
many conifers are _compound strobili_. The central stem produces bracts and
in the axil of each bract is a _cone scale_. Morphologically the cone scale
is a reduced stem. Ovules are produced on the adaxial surface of the cone
scales.
*** Gnetophytes
Gnetophyta consists of three genera, _Ephedra_, _Gnetum_ and _Welwitschia_.
All three are typically dioecious, although some _Ephedra_ species exhibit
monoecy. In contrast to the conifers, which have simple pollen strobili and
compound seed strobili, gnetophytes have both compound pollen and seed
strobili. The seed strobili of _Ephedra_ and _Gnetum_ are reduced, with
_Ephedra_ producing only two ovules per strobilus and _Gnetum_ a single ovule.
<gallery> Image:Welwitschia-bug Probergrothius-Angolensus.jpg|Seed cones of
_Welwitschia_ Image:XN Welwitschia mirabilis 02.jpg|Pollen cones of
_Welwitschia_ Image:Ephedra pollen cones.jpg|Pollen cones of _Ephedra_
Image:Ephedra pollen cone wm.jpg|Pollen cone of _Ephedra_ showing
microsporangia Image:Female cone of Ephedra intermedia -
journal.pone.0053652.g002-C.png|_Ephedra intermedia_ seed cone. Image:Gnetum
gnemon BotGardBln1105C.JPG|Seed cones of _Gnetum_ </gallery>
*** Flowering plants
The flower of flowering plants is sometimes referred to as a bisexual
strobilus. Stamens include microsporangia within the anther, and ovules
(contained in carpels) contain megasporangia. Magnolia has a particularly
strobiloid flower with all parts arranged in a spiral, rather than as clear
whorls.
A number of flowering plants have inflorescences that resemble strobili, such
as catkins, but are actually more complex in structure than strobili.
<gallery> Image:Alnus rubra 9819.JPG|Staminate catkins of alder Image:Alnus
rubra 0020.JPG|Pistillate catkins of alder Image:Casuarina cunninghamiana
fruit and leaves01.jpg|Pistillate catkins of _Casuarina_ </gallery>
** Evolution
It is likely that strobili evolved independently in most if not all these
groups. This evolutionary convergence is not unusual, since the form of a
strobilus is one of the most compact that can be achieved in arranging lateral
organs around a cylindric axis, and the consolidation of reproductive parts in
a strobilus may optimize spore dispersal and nutrient partitioning.
** Etymology
The word _strobilus_ is related to the ancient Greek _strobilos_ = whirlwind.
The Hebrew word for conifer cone, _itstrubal_, is an ancient borrowing from
the Greek.
According to Liddell & Scott, the Greek: _strobilos (στρόβιλος)_ had many
meanings, generally of anything twisted up...hence of the hedgehog,... of an
egg-shell,... as a name of various twisted or spinning objects. For example:
1. a kind of seasnail...
2. a top...
3. a whirlpool, a whirlwind which spins upwards...
6. the cone of the fir or pine, fir-apple, pine-cone,… also of the tree itself.[1]
** References
[Reflist]
- Gifford, E. M. & Foster, A. S. (1988). _Comparative morphology of vascular plants_ , 3rd ed. New York: WH Freeman.
[Authority control]
Category:Plant morphology