Word of the Week: Sporangium

sporangium [ spuhran-jee-uhm ] noun, plural sporangia: a sac or receptacle in which reproductive spores are produced and stored

 

The sporangia of native Adiantum pedatum (maidenhair fern) appear in narrow bands on the underside of the pinnules near the lobed tips, which fold over partially covering the sori. Image © Mary Free

Although sporangia, in which spores are produced and stored, are often associated with fungi and seedless plants, such as bryophytes (e.g., mosses) and ferns, they occur in all plants sometime during their life cycles.

Mosses have a single sporangium at the terminus of a long stalk. In ferns, sporangia appear in clusters called sori, located on the undersides of some fronds or in bead-like aggregates, sometimes on separate fertile fronds. The leaves that bear the sporangia are called sporophylls.

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Comparable structures in conifers are located on the strobili. In the male stobilus or microstrobilus, the sporophylls are called micosporophylls and the sporangia, microsporangia, which produce the pollen. In most microstrobili, the microsporangia are located on the abaxial (under) side of the micosporophylls. In Taxaceae (yew) the microsporangia surround a central stalk. (Schulz, et. al. 2014) The number of microsporangia per micosporophyll differs among species and even within a species. In Pinus (pine), there are two micosporangia per micosporophyll. In the female strobilus or megastrobilus of pine, two megasporangia, which develop into seeds, appear on the adaxial (upper) surface of the megasporophyll (scale-like structure) of the seed cone.

Likewise, flowering plants possess microsporangia and megasporangia. The anther of the male reproductive organ or stamen usually contains four microsporangia in which pollen grains develop. Megasporangia occur inside the female ovules, which develop into seeds.

References

Schulz C, Klaus K, Knopf P, Mundry M, Dörken V, Stützel T. 2014. Male Cone Evolution in Conifers: Not All That Simple. American Journal of Plant Sciences, 5: 2842-2857. DOI: 10.4236/ajps.2014.518300.

Carter S, Lumen Learning. Introduction to Seedless Plants. Lumen Learning. License: CC BY: Attribution. [accessed 13 June 2021].

 

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