Sporangium

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A sporangium (pl., sporangia) is a plant, fungal, or algal structure producing and containing spores.[1] Sporangia, also known as sporanges (sing., sporange)[2], occur in angiosperms, gymnosperms, ferns, fern allies, bryophytes, algae, and fungi. Their spores are sometimes called sporangiospores.

Contents

Types

Microsporangia make up the anthers of the stamens of flowers, and the pollen-producing structures on the microsporophylls of male conifer cones or cycad cones.

Megasporangia are the comparable "female" structures on these plants, associated with the flower carpel and the megasporangial cone.

On ferns, the mature plant is a sporophyte that develops sporangia, tiny, stalked sacs which contain spores. The sporangia may cover the entire underside of the leaf, or occur in lines or clusters called sori. The sporangia are always borne on what is anatomically the underside of the leaf, (the abaxial surface), even if this surface is turned upward. The lycophytes, in contrast, always bear their sporangia on the upper, adaxial surface. A fern may bear sporangia on all leaves or on specialized leaves called sporophylls. Most ferns produce haploid spores.

In mosses, the little case that rises above the vegetative growth on a thin stalk is a sporangium often called a capsule that, as in ferns, produces meiospores. This sporophytic (diploid) growth arises out of the gametophytic (haploid) archegonium after the ovum is fertilized. The sporophyte initially has some chlorophyll, but later turns brown and becomes dependent upon the gametophyte for nutrition, which is absorbed through the foot (base of the stalk), embedded in the archegonial tissues.

Eusporangia and leptosporangia

Categorized based on developmental sequence, eusporangia and leptosporangia are differentiated in the vascular plants.

  • In a leptosporangium, found only in ferns, development involves a single initial cell that becomes the stalk, wall, and spores within the sporangium. There are around 64 spores in a leptosporangium.
  • In a eusporangium, characteristic of all other vascular plants and some primitive ferns, the initials are in a layer (i.e., more than one). A eusporangium is larger (hence contain more spores), and its wall is multi-layered. Although the wall may be stretched and damaged, resulting in only one cell-layer remaining.

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