Summary of sporangium development
From Smith, Cryptogramic Botany:
Liverworts: Embryo divides to form outer layer (ampithecium) that gives rise to jacket layer and inner mass (endothecium) that gives rise to archesporium (cells of which divide to produce sporocytes and nurse cell, may also produce elators).
Hornworts: Embryo divides to form ampithecium that gives rise to jacket layer and primiary sporogenous layer, and endothecium that gives rise to sterile columella in all but one species (where it gives rise to sporagenous tissue). Jacket layer is 4-6 cells thick, and outer layer develops into epidermis. Sporagenous tissue gives rise to sporocytes and filaments of sterile cells called pseudoelators.
Sphagnum: Upper tier of cells in the embryo divides to form endothecium that gives rise to sterile columella and ampithecium that gives rise to outer sterile layer and inner archesporium. Archesporium gives rise to sporogenous layer two to four cells thick. Outer sterile layer gives rise to jacket layer 3 or 4 cells thick.
Eubrya: Early division of capsule gives rise to multilayered ampithecium and endothecium (with ampithecial cells and endothecial cells). Endothecium (usually) gives rise to archesporium and columella. Columella cells adjacent to archesporium remain small and develop into inner spore sac. Ampithecium develops into a multilayered structure, including layers with and without chloroplasts and an epidermis.
Psilophyta: Paired sporangia (a synangium or maybe a reduced sporangiophore) develop from a single cell. First cell division leads to a jacket initial and an archesporial (primary sporogenous) cell. Repeated periclinal divisions of jacket initial lead to jacket layer four or five cells thick and divisions of archesporial cell lead to many sporogenous cells. No tapetum develops. Near maturity, irregular clumps of sporogenous tissue divide to give rise to spore mother cells, remainder disintegrate
Lycopods: Sporangia borne on sporophylls. Early cell division leads to a layer of jacket initials and an archesporium, which divides to form a mass of sporogenous tissue. Nearly all cells in this tissue function as spore mother cells that divide to for tetrads of megaspores. Tapetum is formed from innermost layer of jacket cells and outer layer of sporogenous tissue. Unlike most pteridophytes, tapetum does not break down during sporogenesis.
Selaginellaceae: Has microsporanigia and megasporangia borne on microsporophylls and megasporophylls that are always in strobili (maybe in same or different strobili). Development of mega- and microsporangia is the same up to sporocyte stage. One or multiple cells divide to form outer jacket initial(s) and inner archesporial cell(s). Inner cells develop into mass of sporogenous tissue while outer develop into jacket layer two cells thick, outer layer with thick-walled cells and inner layer with thin-walled cells. A distinct tapetum develops from the outer layer of sporogenous cells.
Isoetaceae: Each sporophyll bears a single flattened sporangia between the ligule and the leaf base, which is covered by a membranous outrgrowth from the epidermis just below the ligule called a 'velum. Early development of mega- and microsporangia is similar. Several cells divide to form jacket jacket initials and archesporial cells. Archesporial cells divide to form mass of sporogenous tissue. Later in development, this is divided into blocks of fertile cells divided by sterile cells. The sterile cells mature into trabeculae, that incompletely divide the sporangium chamber. Sporogenous cells adjacent to trabeculae and jacket layers form a tapetum that is generally two cells thick. Remaining sporogenous cells may become sporocytes. Jacket layer may become 3 or 4 cells thick.
Equisetum and allies: Sporangia are borne on branching sporangiophores and are associated with sterile bracts. Sporangiophores are clustered on the plant axis alternating with bracts (in extinct taxa), but it is not strictly correct to call it a strobilus, since it is not composed of sporophylls. Fossil taxa are a mix of hetero- and homosporous species. Equisetum has strobili with clusters of sporangiophores. Sporangia are of the eusporangiate type in that they are not entirely derived from a single initial cell, but all of the sporogenous tissue can be traced to s single cell. First cell division gives rise to inner cell that will give rise to the sporogenous tissue and outer cell that gives rise to part of the jacket layer, the remainder coming from cells lateral to original cell. Jacket layer is several cells thick, with inner layer functioning as tapetum. Tapetum and inner jacket layers disintegrate during development. Disintegrated SMCs and tapetum and jacekt cells form a liquid in which spores float. Spores form an outer exosporium that splits into four strips called elaters.
Ferns: Sporangia may be borne on the margin of a leaf blade, or on the abaxial surface. May be scattered over the surface or grouped in clusters (sorus). The sori may be covered by an indusium. In eusporangiate ferns, sori may be borne on a specialized part of the leaf blade (fertile spike)
Two types of sporangium development:
Eusporangiate ferns: Sporangia develop from more than one initial cell. Each sporangium contains an indefinite large number of spores and has a jacket layer more than one cell thick.
Ophioglossales: The fertile spike grows from a pyramidal apical cell which produces four quadrants of cells. Strips of epidermal cells (2 to 3 cells wide and several cells tall) on the two quadrants that are perpendicular to the leaf blade develop into sporangiogenic bands which then become three or 4 cells thick. The band differentiates into blocks of sterile cells and archesporial cells. Each block of archesporial cells divides to form a large number of sporogenous cell. The cells in the band external to the archesporium divide periclinally to form a jacket layer, and the cells between the sporangia also divide. Each sporangium becomes surrounded by a poorly defined tapetum which may come from the outer sporogenous cells or the inner sterile cells (unknown). Tapetum breaks down inot plasmodial mass with persistent nuclei in between SMCs.
Marattitales: Sporangia borne on abaxial surface of leaf blade, grouped in sori. In most genera, sporangia laterally fused to form a synangium. Sporangium development begins with a single sporangial initial cell that divides to produce archesporial cell and jacket initial. Archesporial cell divides many times to for sporogenous tissue of 500 or more SMCs, and jacket initial divides to form part of jacket layer. Remainder of jacket layer is formed from cells adjacent to sporangial initial. Jacket is several cells thick, with layer closest to sporogenous tissue forming a tapetum.
Leptosporangiate ferns: Sporangia develop from a single initial cell, jacket layer one cell thick, sporangia with a definite number of spores, and differentiation of the tapetum from a single internal cell of a developing sporangium. May be homosporous or heterosporous. Heterosporous families have sori or groups of sori enclosed in a many celled envelope superficially resembling a seed coat called a sporocarp.
Osmundaceae: A single sporangial intial divides to produce archesporial cell and jacket initial. Division of jacket initial and daughter cells is always anticlinal (thus the jacket layer one cell thick). The archesporial cell cuts off flat cells from each of its faces which have been called tapetal cells, but which do not have the typical form a of cells in a tapetum. The remainder of the archeporial cell becomes the primary sporogenous cell. It goes on to produce a large number of sporogenous cells, the outer layer of which functions as a tapetum and eventually disintegrates, while the rest become SMCs. Sporangia are borne on stalks that arise from cells other than the sporangial initial.
Schizaeaceae: Sporangium and stalk arise form single initial cell. First division produces lower cell that will give rise to stalk and upper cell with three cutting faces that divides a variable number of times. Last three cells cut off become jacket layer, others go to stalk. Apical growth ends with a periclinal division to form jacket initial and archesporial cell. Archesporial cell cuts off a tapetal initial from each of its four cutting faces. These divide to form a tapetum two cells thick. The remaining cell is the primary sporogenous cell which divides to form SMCs. Tapetum breaks down.
