Osmunda protoleptosporangiopsida, a genus of ferns, exhibits both living and fossil forms with reproductive characteristics intermediate between other fern categories. These ferns thrive in tropical and temperate regions, typically in shaded, cool habitats, and are recognized for their distinct morphology such as thick, long-lived prothalli, massive sporangia, and unique leaf structures. Economically, they are utilized in orchid cultivation and valued for their ornamental foliage and edible young leaves.

1. OSMUNDA
PROTOLEPTOSPORANGIOPSIDA
Osmundaceae

5.  Both living and fossil forms
 Members intermediate between eusporangiopsida and leptosporangiopsida

6. Resemblance with eusporangiate ferns
 Eusporangiate development of sporangia
 Massive sporangia wiyh large number of spores
 Antheridia has many wall layers and produce
many antherozoids
 Prothallus- thick, massive and long lived
 Indistinct endodermis, presence of mucilage
canals near vascular bundles
 Presence of stipule at the base of petiole

7. Resemblance with leptosporangiate
ferns
 Tapetum originate from archesporial cells
 Primitive type annulus
 Thin walled stomium
 Sporangial wall single layered
 Projecting type antheridia and archegonia
 Prothalus lack endophytic fungus and is of cordate type
 Prone type embryo development- first division of
zygote vertical

8. Osmunda
 Wide distribution- tropical and temperate
 12-14 sps
 In India- 5 sps- O.regalis, O.claytoniana, O.javanica, O.
japonica, O.cinnamomea
 Grows in higher altitudes usually
 Prefer shaded and cool habitats
 Very much restricted in distribution- in isolated patches

9. Morphology
 Medium sized ferns
 A few- O.cinnamomea- 2-3 meters
 Rhizome- wholly subterranean, upright, short, stumpy, sparingly
branched- dichotomous
 Rhizome is profusely beset with older leaf bases which are
sclerenchymatous- additional strength to rhizome- are arranged in
close spirals- on entire surface
 Near the base of leaves- adventitious roots arise from rhizome
 Roots- hard and rough, black or brown, profusely branched and has
brown root hairs below their tips
 Rhizome with leaf bases and tufts of roots- may reach a foot or so
in diameter

10.  Circinate vernation present
 Leaves pinnately compound- unipinnate or bipinnate, length- 2-3 meters
in some sps
 Leaf base flattened to form stipule like expansion
 Leaflets leathery, variously incised
 Older lower leaflets – larger in size and gradually become smaller towards
the distal end- to give a conical appearance
 Young leaves covered with unbranched multicellular hairs which fall off at
maturity
 Leaves arranged in close spirals and form a basket shaped crown at the top
of rhizome

11.  Leaves- monomorhic/dimorphic
 Monomorphic-( O.regalis, O.claytoniana) only one type of leaves with
dimorphic pinnae- some pinnule sterile others fertile- segregation of
photosynthetic and fertile functions in the same leaf
 Dimorphic- (O.cinnamomea, O.japonica)two types of leaves- sterile leaves
and fertile leaves. Fertle leaves- no green lamina- have only sporangia
directly borne on the branches of rachis

12. Anatomy
 Rhizome-
 No definite epidermis
 Outer cortex- several layers of thick walled cells, outer boundary is irregular
due to persistent leaf bases
 Cells are dead and black coloured
 Numerous leaf traces present here
 Leaf base vascular bundles are also seen
 Gives mechanical strength

14.  Inner cortex- few layered, thin walled cells fille with starch grains
 Some leaf traces are also present
 Leaf trace bundle- C shaped, has its own endodermis and 2-3 layered
pericycle
 Phloem completely surrounds the central xylem strand
 Xylem- horse shoe shaped
 Protoxylem in the concave side as small masses

15.  Endodermis-
 Next to inner cortex- endodermis- has distinct casparian strips
 Endodermis- completely surround the stelar region- uninterrupted
 Pericycle- 2-3 layerd, parenchymatous next to endodermis

16.  Stele – has many C- shaped xylem bundles surrounded by a continuos ring of
phloem elements
 Protoxylem lies in the concavity of the xylem bundle
 Number of xylem strands varies in different sps
 Pith- conspicuous- parenchymatous or a few sclerenchyma strands may be
present
 Stele- is said to be dictyoxylic as it can not completely fulfill the conditions of
a dictyostele

17. Petiole
 Epidermis- single layered parenchymatous
 Has simple multicellular hairs when young
 Few layered sclerenchymatous hypodermis
 Cortex- broad, parenchymatous
 Vascular bundle single, horse shoe/ C shaped
 Has a central xylem core surrounded by phloem on all sides
 Protoxylem groups- several along the concave side
 Metaxylem forms major part of the xylem tissue
 Many mucilage canals present towards the concave side of the vascular
bundle

19. Leaflet
 Has upper and lower epidermis- parenchymatous
 Stomata- on lower epidermis
 Mesophyll undifferentiated- has thin walled parenchyma cells with
intercellular spaces of varying dimensions
 Cell contain chloroplast
 Single concentric vascular bundle is present

20. Root
 Endogenous in origin from rhizome
 Distinct epidermis in young roots
 Later it is replace dby outermost layer of cortex- exodermis
 Next to epidermis- a few layered hypodermis of thick walled small cells
 Rest of the cortex- parenchymatous
 Endodermis- distinct
 Pericycle- 2 layered and thin walled
 Stele- usually diarch/ in some triarch

21. Root - osmunda

22.  Two xylem bundles meet at the centre
 Protoxylem- exarch
 No pith
 Phloem- as two patches on either side of the xylem masses

23. Reproduction
 Sporophyte- homosporous
 Fertile pinna arise as branches of the rachis
 Clusters of sporangia are borne on these thinned out
leaflets- known as tassels of sporangia.
 In some sps- lower parts of pinna – fertile and distal
parts sterile and photosynthetic
 In some. Sterile pinna bear sporangia along the
margins
 In O.claytoniana, fertile pinna restricted to the
middle of the leaf
 Pinna bear many sporangial clusters- known as tassels
 A sporangial tassel corresponds to a section of the
leaflet
 Sporangia- naked- not covered by indusia or hairs

26.  In O.claytoniana, an abnormal condition
was seen for the sporangia in one study
 Some sterile pinnae were seen to possess
sporangia as sori on their abaxial surface-
may be a transition zone between sterile
and fertile pinnae

27. Sporangia
 A mature sporangium – massive, short
stalked and pyriform structure
 Stalk is many celled and varies in length
 Capsule has- single layered jacket cells
 Tapetum- 3 layered- do not disorganise to
form plasmodial fluid
 But in O.claytoniana, tapetum is plasmodial
 Tapetal layer is derived from primary
archesporial cell
 Spore mother cells undergo meiosis to form
128-512 haploid spores

30.  Mature sporangium develops a
transverse group of thick walled
cells on one side- annulus
 A vertical row of thin walled cells
opposite the annulus represents
the line of dehiscence
 As the annulus dries and shrinks,
sporangial wall is pulled apart
along the line of dehiscence to
liberate the spores

31. Sporangial development
 Sporangia appear as a small protuberance on
the fertlie pinna
 In each such protuberance, a single sporangial
initial becomes distinct by its larger size,
distinct nucleus and abundance of cytoplasm
 Sorangial initial divides into an outer smaller
cell (primary jacket cell) and inner larger
cell(primary archesporial cell)
 primary archesporial cell divides to form 3
peripheral cells enclosing a central primary
sporogenous cell
 The 3 peripheral cells divide periclinally and
anticlinally to form the tapetal layers
 In some sps the inner layer of tapetum is
derived from the primary sporogenous cell

32.  Sporangial stalk is derived
from the surrounding cells
partially or fully – so the
devpt cannot be traced to a
single cell as in
leptosporangiate ferns- so it
is named as
protoleptosporangiate
development

34. Gametophytic generation
 Starts with haploid spores
 Spores- spherical, has adistinct triradiate mark
 Spore wall- outer exine- thick ornamented
 Inner- intine- thin
 Has a central distinct nucleus surrounded by
cytoplasm and numerous chloroplasts
 Remain viable for one week

35. Spore germination
 Spore absorbes water, exine ruptures along the
triradiate mark, intine comes out as a small conical
papilla
 It divides by transverse wall into primary rhizoidal cell
and large prothallial cell
 Rhizoidal cell forms the first rhizoid
 Prothallial cell has numerous chloroplast
 It grows exactly opposite the first rhizoid- bipolar
germination
 In some prothallial cell divides by a few transverse
walls to form a green filament
 The terminal cell of the filament divides by two

36.  The lower cells of the filament divide longitudinally
 apical cell cuts off cells to its right and left sides in an alternate
walls, then each by vertical wall to form an outer cell and inner
cell
 Inner cells divide by horizontal walls which add to the thickness
of the midrib
 Outer cells divide rapidly, overgrow the apical cell giving the
prothallus a heart-shaped appearance
 Apical cell may remain functional for a longer period and cut off
cells laterally and also to the dorsal and ventral sides
 Finally an elongate heart shaped prothallus with a distinct cushion
below the notch is formed
 Mature prothallus- 3-6 cms long

37.  Mature prothallus- elongated, unbranched,
dorsiventral, green and cordate
 Length 2-3 cm
 Has a distinct midrib
 Midrib- thick and cishioned below the notch
 Rhizoids- arise from ventral side, usually
unicellular
 Monoecious and protandrous, flat, ribbon like and
has smooth/ slightly wavy margin
 Sometimes- prothallus may be unisexual

38. Sex organs
 Antheridia- projecting type
 Terminal/marginal/ even ventral in posotion
 Large and globular
 Stalk may or may not present
 Has a single layered jacket. Jacket cells
contain chloroplast
 A triangular opercular cell is present, which
will open to liberate the male gametes.
 Spermatozoids- minute, coiled and
multiciliate structure
 Has two coils- posterior coil slightly broader
than anterior one

39.  Archegonium- produced on ventral side of
prothallus
 Has a projecting neck from the median
cushion
 Neck has 4 vertical rows of cells, each row
6 cells in height
 Neck encloses a single binucleate neck canal
cell
 Venter is embedded in the prothallus tissue,

41. Fertilization
 Usual process, neck canal cell and ventral
canal cell disorganise and become
mucilaginous
 It absorbes water swells up and forces the
apical tier of cells apart, making a passage
for the sperms to enter and fertilization
occurs and zygote (2n) is formed

42. Embryogeny
 Dipoid zygote is established
 It secretes a thick wall to form the oospore inside
the venter
 It divides by a vertcal wall to form 2 equal cells
 They divide by another vertical wall right angle to
the first vertical wall to form quadrant stage
 the epibasl half form leaf and stem
 Hypobasal half form foot and root.
 No suspensor- so the development is exoscopic.

44.  Quadrants divide to form octant by
another transverse wall formation
 Further divisions are irregular
 Root initial forms the primary root,
foot is haustorial
 Young leaf appears as a conical
protuberance on one side
 Stem apex appears on one side of the
leaf apex and grows into an
underground stem after the primary
root and leaf have established

45.  Apogamy – from the prothallus the sporophyte
develop as a vegetative outgrowth in some sps
 In O.javanica from the sporophytic tissue
production of antheridia has been reported
 Economic importance- root and stem fibres
used for orchid cultivation
 As ornamentals- for beauty of the foliage
 Young leaves used as vegetable by some people