Sporangia are Spore bearing structure. • May be eusporangiate or leptosporangiate. • Homo- or Heterosporous. • Terminal/ Lateral/ aggregated into specialized structures. Tassel is regarded as primitive and acrostichoid condition as advanced. The sporangia on expanded sporophyll are with or without the indusium(protective covering). • The sori lacking indusia are exindusiate or naked (Gleicheniaceae).

1. An Assignment on Pteridology
Topic: Soral & Sporangial Characters in Pteridophytes- A comparative Account
Submitted to,
Dr. Lesly Augustine
Assistant Professor
Dept. of Botany
Submitted by,
Anakha Mariya Jacob
21PBOT2476
1st
year M. Sc Botany

2. Sporangia
• Spore bearing structure.
• May be eusporangiate or leptosporangiate.
• Homo- or Heterosporous.
• Terminal/ Lateral/ aggregated into specialized structures.
• Specialized structures may be sporophyll/ strobili/sporocarp/sorus.
• Large sporangia are found in Ophioglossales & Marattiales.
• The more primitive families of ferns: Osmundaceae, Gleicheniaceae & Schizaeaceae
also have large sporangia but the walls are thin and the annulus unspecialized.
• The annulus is presumed to have originated by gradual differentiation within the surface
layer until complete dimorphism of all types resulted.
• Sporangia of Actinostachys, Schizaea, Stromatopteris, and Osmunda show
intergradation between surface cells and annular cells.

3. Dehiscence of a Sporangium
• In the eusporangiate ferns, dehiscence is by a slit and is fundamentally longitudinal in
all cases.
• In the transitional family, Osmundaceae, Osmunda & Todea, the annulus is located near
the tip but on to one side and forms a cleft that runs over the top of the sporangium and
down the opposite side. The sporangia open like a calm.
• In the leptosporangiate ferns,
❑ the annulus may form a cap at the distal end of sporangium as in Lygodium resulting
in longitudinal dehiscence.
❑ be obliquely placed as in Gleichenia, Hymenophyllum & Loxsoma leading to
oblique dehiscence
❑ Run over the top of a sporangium in line with stalk i.e., in a vertical position as
in Leptochilus resulting in vertical dehiscence.

5. • Sporangial initials are superficial in position and periclinal divisions of these cells result
in outer wall cells and inner primary sporogenous cells.
• Have multi-layered walls during ontogeny.
• More spore output compared to leptosporangiate type.
• Examples: Psilotum, Botrychium, Lycopodium, Equisetum, Selaginella

6. • Originates from a single superficial cell and the mature sporangium has a single-layered
wall.
• Sporangial initial divides by a transverse wall and the entire sporangium is derived from
the outer cell.
• The inner cell remains inactive in most leptosporangiate ferns or occasionally divides,
and the cells formed to contribute to the sporangial stalk.
• From the outer cell using three successive divisions, is formed a tetrahedral apical cell.
• This apical cell cuts off cells parallel to its three lateral faces.
• The lower segments form a three-rowed stalk and the uppermost segments contribute
to the sporangium wall.
• Finally, the apical cell divides periclinal to form an outer jacket cell and an inner
primary sporogenous cell.
• Jacket cell together with the uppermost cells formed by apical cells give rise to the one-
cell thick sporangial wall.
• Simultaneously, the primary sporogenous cell cuts off four tapetal initials from which
is derived the two-layered tapetum.
• The inner cells divide to form sporogenous tissue and finally form sporocytes.
• Spore output is less compared to that of the eusporangiate type.
• Example: Adiantum, Lygodium, Pteris, Gleichenia
• Sporangia of Osmundaceae in their structure and development is a transitional type
between eusporangiate and leptosporangia.
• The entire sporangia is not traceable to a single initial cell.
• The sporangium has a massive stalk partly contributed by neighboring cells.

7. • The form of initial cell destined to form sporogenous cells, tapetum, and wall of
sporangium is variable.
• At times it resembles the comparable cells of a eusporangium i.e. it is truncated at the
base but in some cases, it is similar to the initial cell of a leptosporangium i.e. pointed
at the base.
• Spore output is transitional, more than a leptosporangium and less than a sporangium.
• Example: Osmunda, Todea

11. • Borne singly on the apices of some aerial branches.
• Each sporangium is an oval or slightly cylindrical structure with a little greater diameter
than that of the aerial branch on which it is developed.
• They were 12 mm long and 4 mm in breadth in R. major and 4 mm long and 1 mm
broad in R. gwynne-vaughani.
•Five cells thick wall.
•1 cell thick cuticularized epidermis was followed by 3
cells thick middle layers of thin-walled cells.
•The inner-most layer was 1 cell thick tapetum.
•The wall was surrounding a spacious sporangial cavity.
•Columella absent.
•Homosporous with numerous spores.
•No special mechanism of sporangium dehiscence.
•The liberation of spores by the disintegration of the
sporangial wall.

12. • Eusporangiate development.
• Synangium- fusion of 3 sporangia.
• Borne on the axils of small leaf-like
appendages.
• Neither its outermost sporogenous cell
nor the innermost jacket cells develop into the
tapetum.
• The spores formed in the tetrads are colourless and reniform.
• Homosporous.
• On the middle part of the stem sporophylls are laxly borne intermixed with vegetative
leaves.
• The sporophylls resemble the vegetative leaves with bifurcate tips and bear single
sporangia on the adaxial face is little above the bases.
• No vascular connection leading to the sporangia.

13. • Found singly on fertile leaves known as sporophylls.
• Sporophylls bearing sporangia densely aggregated along stem to form either branched
or unbranched called strobilus.
• Strobili are terminal.
• Reniform, orange to yellow.
• Unseptate sac-like structure with a narrow or massive stalk.
• Homosporous.
• Eusporangiate development.
• Dehiscence by transverse rupture of sporangium apex along the line of stomium.
• Heterosporous.
• Largest among all known extant spore-producing plants.
• Highest spore output.
• 50-300 megaspores/ megasporangium.

14. • 150,000-1000,000 microspores/microsporangium.
• Sporangium traversed irregularly and incompletely by plate-like trabeculae.
• Trabeculae surrounded by tapetum.
• Microspores elongate, 45 microns long.
• Megaspores 250-900 microns in diameter.
• All leaves are potential sporophylls.
• Sporophylls are ligulate.
• Eusporangiate.
• In microsporangia the
sporocytes differentiate after the
formation of trabeculae, while in
megasporangia the sporocytes
differentiate before the formation
of trabeculae.
• No dehiscence
mechanism.
• Spores are released only
after the death and decay of the sporangia.

15. • Sporangia are produced on the axils of ligulated leaves called sporophylls.
• The sporophylls are compactly arranged to form cones or strobili.
• Heterosporous.
• Eusporangiate.
• Sporangia reniform to ovoid with a short stalk.
• In microsporangia, all sporocytes except 10-20% from form microspores.
• Each sporangium has 2 layered wall, a layer of tapetum and sporogenous tissue.
• Spores are with a prominent triradiate mark and characteristic ornamentation.

18. • Reflexed sporangia are produced on sporangiophores which are aggregated into definite
cones or strobili at the apex of fertile shoot.
• Homosporous.
• Eusporangiate.
• Strobilus is composed of
➢ sporangiophores: an axis with whorls of stalked, peltate structures.
➢ Immediately below the whorls of sporangiophores, the axis bears a small or large ring
like outgrowth, the annulus.

19. • Each sporangiophore is umbrella like in shape.
• 5-10 sporangia on the underside of each sporangiophore disc.
• Sporangia: slender stalk bearing a peltate and hexagonal disc on the under surface of
which there are elongate, cylindrical hanging sporangia.
• Each sporangium is an elongated, sac-like sructure attached to the inner side of stalked,
sheild-shaped sporangiophore.
• At first, the wall is 3-4 layered but when mature 2 jacket layers remain.
• Internal to the jacket, a mass of sporogenous tissue forming spore tetrads is present.
• When spores mature, the axis of the strobilus elongates with the result that the
sporangiophores are separated.
• The sporangium dehisce by means of a longitudinal slit.
Spores of Equisetum
• Spores are globular/ spherical in shape.

20. • Thick wall with 4 concentric layers:
❑ Innermost cellulosic, delicate intine.
❑ Exine
❑ Middle layer
❑ Thick epispore
• Intine and exine are products of spore-protoplast.
• Middle layer & Epispore are formed around the intine & exine by the activity
of the periplasmodium.
• Epispore splits to 4 spirally arranged ribbon like bands called elaters, flattened
at the tips.
• The bands are free from the spore wall except for one common point of
attachment.
• The elaters are hygroscopic.
• When moist, they are spirally coiled round the spore and uncoil
and become extended as the spore dries out.
• Elaters are different from those found in bryophytes.

21. • When the spore matures, elaters uncoil and this expansion of the elaters help in
the dehiscence of sporangium.
• In shedding, these elaters uncoil, become entangled with the elaters of other
spores and thus the spores are shed in groups rather than singly.
• The elaters aid in spore dispersal.
• The spores contain chloroplast.

26. • Tassel is regarded as primitive and acrostichoid condition as advanced.
• Sori are described to be derived from the tassel in three ways:
1. A superficial sorus can be obtained from the tassel by the development of a blade on
the axis. This is seen in Osmunda-Todea series.
2. A blade with monosporangial sori as in Lygodium can be obtained by a similar
expansion as in Osmunda-Todea series but along the axis of sporangial attachment. The
solitary sporangia later form sori by increase in number. This can be visualized
through Lygodium, Mohria and Gleichenia.

27. 3. The tassels can change into marginal sori by the webbing of sterile stalks of fertile tips.
This may be seen in Anemia, Schizaea and Trichomanes series.
• Protection of young sporangia during ontogeny is provided by circinate vernation.
• The sporangia on expanded sporophyll are with or without the
indusium(protective covering).
• The sori lacking indusia are exindusiate or naked (Gleicheniaceae).
• In forms having marginal sori, the indusium might become a cup or pouch-
like structure formed by extension of the abaxial and adaxial margins of leaf
(Trichomanes, Davallia, Dicksonia).
• In forms having superficial sori, the indusium is essentially an outgrowth of leaf
epidermis.

28. • The indusium is vairable in its form and extent.
❑ It may be delicate strip attached along one side only-Unilateral indusium ( Asplenium).
❑ Reniform and attached at sinus (Dryopteris).
❑ A peltate disc (Polystichum, Cyrtomium)
❑ Circular
❑ Horse shoe shaped
❑ Cup-shaped
• Instances where reflexed leaf margin provide protection to sporangia are refered as false
indusia.

29. • The indusium in superficial sori can be seen to have undergone a further change. The
point of attachment migrated from margin to the centre of receptacle and it became a
radially symmetrical structure.
• From a radially symmetrical indusium, an elongate lateral indusium is derived by
the extension of the area of attachment along on side. This is seen in Aspidium-
Athyrium-Asplenium series.

30. • Fertile leaves are alike the sterile leaves in form.
• Sporangia are borne in distinct sori on the abaxial side of the leaves.
• Sori are superficial.
• Oblong rings of free sporangia occur, each over a vein.

31. • They are sessile and arise in two rows beneath veins towards the margins of the
pinnules.
• All the sporangia in a sorus are free from each other.
• Eusporangiate.
• Simple.
• Free sporangia have a band of enlarged cells of thicker walls.
• Each sporangium has a several layered thick wall, with stomata in the outermost layer.
• High spore output: 1450-7000.
• No annulus, sporangia open by slits on the inner side, or by pores near the apex.
• Sporangia are produced in two rows on a fertile spike that arises at the junction of the
petiole with the sterile lamina, on its adaxial surface.
• Spike is a simple, more or less cylindrical and stalked structure with laterally
fused elongate synangia.

32. • Generally, a single spike is associated with a leaf but in O. palmatum several spikes are
present on a single leaf.
• The fertile spike bears two marginal rows of sunken and laterally fused sporangia.
• The apical region of the spike which is somewhat conical and devoid of sporangia
projects as a sterile process.
• The length of the spike varies according to the species.
• Prominent vascular bundle and stomata are present on spike. A ring of bundles become
organized within the stalk of the complex. At higher levels, the bundles on the adaxial
side become more closely grouped and enter the fertile spike.

33. • The number of sporangia in each spike ranges from 6-20, according to the size of the
plant.
• A number of vascular strands run longitudinally up the middle and
from these strands develop the lateral branches which lead to the sporangia.
• At maturity, each sporangium is spherical or oval and remains embedded in tissue of
the fertile spike.
• The wall of the sporangium is several layers thick.
• Stomata are present in the sporangium wall.
• Homosporous.

34. • Below it, is tapetum that comes from the innermost wall layer.
• No special dehiscence mechanism. It takes place by drying out and shrinking of
the sterile tissue within the spike.
• Each sporangia opens by a transverse slit in the sporangial wall.
• Spores as many as 10000.
• Bower (1896) suggested that fertile spike is a single septate sporangium growing on the
adaxial face of the leaf.
• This interpretation was later on (in 1911) rejected by Bower himself.
• According to present considerations, the fertile spike is regarded pinna-like in nature.
• It has been held by Goebel (19150, that the spike represents a single pinna.
• According to Roeper (1859), the spike represents two basal pinnae whwich have
fused laterally, during the ontogeny to form the spike. The interpretation
is supported by the course of vascular supply to the spike. The spike exhibits the

35. same vascular supply as would ordinarily go to a pair of pinnae. Later this
interpretation was supported by Chryslar (1910) and Bower (1926).
• According to Zimmermann (1930), the fertile spike and sterile lamina are the divisions
of a leaf, representing a dichotomy.
Soral & Sporangial Characters in Osmunda
• Sporangia do not occur in sori and are attached along the margins of non-laminated
fertile pinnules, forming tassel-like structures:
❑ either on an entire leaf (O. cinnamomea)
❑ on part of it ( O. regalis, O. claytoniana)
• Sporangia are not protected by indusium.
• In O. regalis, the fertile pinnules are found in the distal regions of the leaf.
• In O. claytoniana, the fertile pinnae are restricted to the middle of the leaf.
• In O. Cinnamomea, there are two kinds of leaves, the sterile and fertile.
The fertile leaves are reduced and blade-less.
• Homosporous

36. • Transitional type of sporangial development.
• Lack an indusium.
• During the course of sporangium development, the walls of a group of jacket cells
located near the tip towards one side of the jacket become thickened to form the
rudimentary annulus.
• Mature sporangia is a large pyriform body with short and massive stalk.
• One-layer thick wall.

37. • Dehiscence of the sporangium takes place by vertical split starting from
the rudimentary annulus to the outer side of the sporangium.
• High spore output: 128-512.
• Spores are spherical with a triradiate mark and abundant chloroplast.
• Heterosporous.
• Reproductive structures are flattened bean-shaped, spherical to ovoid, epipetiolar,
stalked sporocarps, inserted a short distance above the petiole.
• Length of the stalk and its point of attachment is variable in different species.
• Normally there is one sporocarp per petiole but in forms like M. polycarpa, there are
large number of sporocarps attached on one side of petiole and in M. quadrifolia the
stalk is occassionally branched forming 2-3 sporocarps per petiole.
• In some species, the sporocarps have distinct external ridge, the raphe and two bumps.
• The raphe represents the end of attachment of the stalk.

38. • One of the bumps is stouter and is present at the end of the raphe.
• The sporocarps have a thick wall resistant to injury and dessication and are reported to
remain viable up to 35-40 years. The outer layer is epidermis made up of single-layered
cuboidal cell with sunken stomata.
• Inside the sporocarp, around the cavity extends a ring of gelatinous tissue.
• There are rows of elongate sori, on either side, extending transversely to the long axis
of the sporocarp.
• Each sorus is borne on an elongate receptacle which is attached to the gelatinous ring,
at its two ends as well as to the wall of sporocarp on one side, along its length; the
other side faces the lumen of sporocarp.

39. • Number of sori in each sporocarp may vary from 2 in M. aegyptiaca to 20 in M.
Quadrifolia.
• Each sorus is enclosed by a delicate diaphragm, the indusium.
• On the crest of the receptacle are borne a number of megasporangia each having
a single large megaspore.
• Along the sides of the receptacle are borne smaller microsporangia each
having numerous microspores.
• The vascular supply to the sporocarp branches from the margin of petiolar trace. From
the main trace arise pinnate series of traces, on each side. These lateral bundles
alternate with one another.

40. • Each of the lateral bundles bifurcates and the vascular supply to the
individual sorus known as placental bundle arises at the point of forking.
• The placental bundle in turn bifurcates to form dorsal and ventral traces.

41. • Towards the lower margin of the sporocarp, there is a network of veins due
to anastomoses of the pinnate series of bundles.
• The sporocarps open only in water, splitting bivalve-like.
• The process is initiated by the absorption of water by gelatinous ring which
expands and frees the sori from the wall of sporocarp by an abscission along the
receptacle. This is followed by the breaking of ring at one end. The broken gelatinous
ring results into an elongate worm-like structure dragging the sori along with it.
• Microspores are small globular cells.
• Megaspores are large, ivory-white papillate structures enclosed by gelatinous layer and
are visible to naked eyes.

42. • Sporangia are aggregated into sporocarps.
• The sporocarps appear in chains or clusters ranging in number from 4 to 20.
• The sporocarps are usually borne on the inner segments of submerged leaves.
• In arrangement, the sporocarps are sympodial.

43. • The shape of the sporocarp varies from globose to ovoid, occasionally flattened also
with ridged surfaces.
• The wall of the sporocarp is made up of two layers of cells. The outermost layer when
young is clad with hairs.
• Externally all sporocarps are alike. But unlike in Marselia, the sporocarps are mono-
sporangiate.
• In each sporocarp there is an elevated receptacle bearing sporangia.
• The receptacle receives a vascular trace from the leaf segment.
• The first one or two sporocarps in each cluster are megasporangiate whereas all the later
formed ones are microsporangiate.
• In a megasporangiate sporocarp, only about 25 mega-sporangia are seen whereas in a
microsporangiate sporocarp, the number is much larger because of the branching of the
receptacle.
• Leptosporangiate.
• Sporangial wall is delicate and single layered, without annulus.

44. • As the spores mature, the tapetal cytoplasm encompassing the spores gets hardened and
forms a mass called ‘massula’.
• After the sporangia are mature the sporocarps get detached from the leaves and sink to
the bottom of the pond.
• The sporocarps open up due to the mechanical decay of their walls. This results in the
release of spores, which rise to the surface where the rest of life cycle is completed.
• Heterosporous.
• Sporocarps are dimorphic: mega- & microsporangiate.
• Sporocarps are monosporangiate.
• Sporocarp wall is bilayered and delicate except at the tip of megasporangiate sporocarp
where it is firm.
• Microsporangia are globose, long stalked producing 64 spores.
• Megasporangiate sporocarp contains one megasporangium which produces 32 spores,
all of which except one degenerates.

45. • In microsporangium, the tapetal plasmodium develops a number of vacuoles. Each
vacuole becomes hardened and divided by partitions into number of alveoli. Each
hardened alveolar material within which the microspores are embedded is called
a massula.
• In some species, the massula develop tubular outgrowths with the anchor shaped tips
called glochidia. These structures helps in attaching the microspore massulae to the
megaspore massulae.
• In megasporangium, tapetal plasmodium divides into 4 massulae. One
of thse envelopes the single megaspore. The other three massulae are grouped above
the megaspore.
• The presence or absence, and form of glochidia on a massula are important
characters, delimiting the species.

46. • The sporangium is covered by a two layered inducium.
• Massulae and megaspores are released by the decomposition of sporocarp wall.
• Homosporous.
• The sorus of Pteris is called coenosorus .

47. • Coenosori are marginal, borne continuously on a vascular commissure connected with
vein ends.
• The sporangia of Pteris form a continuous linear sorus along the margin, hence the
individuality of sori is lost.
• The coenosori are protected by the reflexed margin (false indusium) of the pinnae.
• Sori are of mixed type intermingled with many sterile hairs in between the sporangia.
• Leptosporangiate type.
• A mature sporangium has a long stalk that terminates in a capsule
• The jacket of the capsule is single-layered, but with three different types of cells:

48. (1) A thick walled vertical annulus incompletely overarches the sporangium
(2) A thin-walled radially arranged stomium
(3) Large parenchymatous cells with undulated walls.
• Spores are triangular in shape with trilete aperture, bounded by two walls. The outer
wall, exine, is variously ornamented.
• The sporangium dehisces transversely along the stomium due to the shrinkage of
annular cells.
• Each sporangia produces 48 spores.
• Homosporous.
• Sporangia which are produced in abundance are borne in two rows along the ultimate
veins.

49. • They form spike like structures on the leaf margin.
• A single sporangium occur at the end of veinlet and each is covered by a flap.
• The flap is a false indusium representing an extension of leaf margin.
• The sporangia are born singly, forming “monosporangial sori”
• Each sporangium has a short and thick stalk with a spore number of 128 –256.
• Leptosporangiate development
• Massive bilayered tapetum.
• The annulus is a terminal group of thick – walled cells, confined to distal end
of sporangia.
• The dehiscence is longitudinal , most primitive type in ferns.
• Capsule of the sporangium is pyriform and curved.
• Definite stomium is present and the dehiscence is longitudinal.
• Spores are usually triangular, tetrahedral and trilete.
• Exine is striate.

50. • The upper pinnae are small and fertile, whereas the lower pinnae are infertile.
• The length of the lowest pinna is occasionally smaller than that of the upper pinnae.
• Sporangia cover the lower surface of the fertile pinnae or are located at the tip.
• The sporangia have many sterile, multicellular filaments that are threadlike, with
darkened cells at the end.

51. • This genus gave rise to the word acrostichoid, due to the tightly packed sporangia on
the abaxial side of the lamina (Tindale, 2009).
• Acrosticoid sorus is the most advanced sorus.
• The presence of sporangia and the absence of sori differentiate Acrostichum from other
ferns (Hill, 2006).
• A mature sporangium has a long stalk that terminates in a capsule.
• Exindusiate.
• Mixed type of sori.
• Spores yellow, tetrahedral, minutely tuberculate or roughened, equatorial flange
absent.
• Spores clear to translucent, 1 – 1.5 mm wide, and buoyant.
• Sporangia occur in ring-shaped sori on the abaxial surface of the pinnule.
• Ex-indusiate.
• No segregation of sterile and fertile leaf parts.
• Sori are naked and lie in two rows, one on either side of the mid-rib of the pinnule.

52. • Number of sori on a pinnule varies from 1 to many.
• Sporangia arise on somewhat elevated circular receptacle and vary in number from 4 to
15.
• Size of the sporangia varies with their number within a sorus.
• In the species which have few sporangia, the sporangia occur in a uniseriate ring at the
margin and the centre of the sorus is vacant.
• In other species, the sporangia found in the centre, lying on top of others.
• When examined superficially, a sorus looks like a synangium, but it is not so.
• Mature sporangium is pyriform.
• Young sporangia are usually covered by hairs or scales.
• Sporangia lie on two sides of the midrib of the pinnules.
• Some cells of the jacket are thick-walled and form a distinct annulus whose position is
oblique horizontal.
• Simple sori.

53. • Leptosporangiate development.
• Short and stout stalked sporangia.
• Distinct annulus present.
• Single-layered jacket enclosing varying number of spores.
• Spore outcome:128-1024.
• Each sporangium has a large number of spores and has an obliquely transverse complete
annulus which causes longitudinal dehiscence.
• Spores are trilete in G. circinata whereas monolete in G. bifidus.
• Homosporous.
• Has slightly papillate surface.
• Spores vary in size according to the species.

54. • There is no distinction into fertile and sterile leaves.
• Soru bearing leaves are called sporophylls.
• The sori are born superficially at the distal end of the pinnae. But the sori are not exactly
marginal. They are borne a little behind the tip of the veins, submarginal.
• The sorus bearing margin of the leaf incurls and forms the false inducium.
• The sorus is of the mixed type.

55. • A mature sporangiuim has a stalk made up of three rows of cells.
• The stalk terminates in a globose or biconvex capsule.
• The wall is single layered.
• The sori are covered and protected by reflexed margins of leaflets, which
are membranous structures called false indusium.
• Each sporangium is oblong and consists of a multicellular stalk and the head or capsule.
• Capsule is biconvex.
• Distinct vertical annulus.
• The annulus is separated from the stalk by two or three cells.
• The stomium is separated from both the stalk, and the annulus.
• The rest of the sporangial wall is composed of a few large cells.
• There is an obliquely vertical annulus of 12-24 cells long.
• The sporangium dehisces transversely liberating the spores.
• Leptosporangiate development.

56. • Homosporous.
• Spores are tetrahedral in shape with a triradiate ridge and spore wall is two layered.
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