Give an account of the salient features of Sphagnum and its affinities.

(i) Sphagnum represents ‘peat’ or ‘bog moss’ growing in swamps, ponds or moist places at high altitudes including Himalayas. It renders the water acidic, and has an antiseptic value.

(ii) The upright gametophore with radially arranged leaves, leafy branches and without rhizoids.

(iii) Erect and pendant branches arise from the axil of every 4th leaf. The erect branches are crowded at the tip as ‘coma’ or ‘head’, while too much elongated pendant branches forming the loose mantle around the stem axis at its proximal end.

(iv) The stem axis is differentiated into 3 distinct zones-(a) the axial cylinder or parenchyma, (b) middle zone of thick-walled prosenchyma, and (c) peripheral zone of uni-multiseriate cortex without epidermis.

In old stem the axial cylinder is replaced by prosenchyma, and the cortex with porous cells having fibrous thickenings.

(v) One-celled thick semi-transparent leaf without midrib consists of living green and dead hyaline porous cells in alternate sequence.

(vi) Stem branches have uniseriate cortex including flask-shaped retort cells, each having an apical pore.

(vii) The spongy texture of cortex and porous nature of leaves serve to compensate the absence of rhizoids.

(viii) The growth of shoot axis is due to tetrahedral apical cell.

(ix) The vegetative propagation by gametophore is due to innovation, death and decay of older stem axis, and secondary protonema arising from any living cell.

(x) Sex organs originate from apical cells.

(xi) Sexuality oogamous; gametophore dioecious or monoeciousprotandrous.

(xii) The spindle-shaped and catkin-like antheridial branch may be solitary or in cluster of 2-several. It bears several androgonial leaves arranged spirally or in straight rows in ascending order. Each of the protective leaves as an axillary antheridium.

(a) Antheridium oval – elliptical with numerous androcyte mother cells under the protective cover of uniseriate jacket.

(b) Antheridial stalk – elongated and slightly curved-consists of 2-4 vertical rows of cells, each row 2 celled broad.

(c) Biflagellate antherozoid forms 2-3 spiral coils in clock-wise manner; its major part is of nuclear origin. Flagella are attached to the flagellophore.

(d) Antheridium ruptures apically to form several revolute lobes.

(xiii) A cluster of 3 acrogynous archegonia, including a medianly- placed primary and rest 2 secondary develops at the tip of bud-like globular greenish archegonial branches.

(xiv) The archegonium bears a long stalk, a massive venter and long twisted neck.

(a) The neck, having 6 vertical rows of cells, contains 8-9 N.C.C.

(b) The jacket at the basal end of neck is biseriate and at venter triseriate.

(c) A rosette of 8-more cover cells constitutes the terminal jacket being uniseriate.

(xv) The basal cell of filamentous embryo forms a bulbous or slender haustorium below foot. The haustorium pierces the tip of archegonial branch

but is obliterated with the growing age of developing sporophyte.

(xvi) The sporogonium has a bulbous foot embedded in vagenula, a rudimentary seta and a sub-spherical capsule. It rests at the tip of pseudopodium which elongates to raise high up the sporogonium.

(xvii) Determinate sporophyte is nutritionally independent of the gametophore.

(a) 4-6 layered capsular jacket includes an epidermis with non-functional stomata and chlorophyllous wall layers.

(b) Dome-shaped massive columella is over-arched by a horse-shoe-like spore-sac having uniseriate wall.

(c) The opercular zone is represented by a discoid operculum and an annulus.

(xviii) Presence of calyptra around the sporogonium.

(xix) Dehiscence of capsule is due to separation of lid as per agency of ‘air gun mechanism’.

(xx) The columella originates from endothecium and archesporium from inner amphithecium.

(xxi) Meiospore tetrahedral with a distinct verrucose exosporium. It, on germination, produces thalloid protonema being dorsiventral and l-celled thick chlorenchymatous.

Initially rhizoids arise from the filamentous structure but later on from the base of protonema facing its ventral surface.

(xxii) Production of a single gametophore per protonema by a tetrahedral marginal bud. Protonema disappears soon after the formation of gametophore.

(xxiii) Any marginal cell of primary protonema can produce secondary protonema.

Sphagnum occupies an unique position among the bryophytes. It has several features similar to Hepaticopsida, Anthocerotopsida and Bryopsida besides its own individual characters. Quite naturally it stands in between Anthocerotopsida and Bryopsida. The similarities can be enumerated as follows:

Sphagnum resembles more close to the members of Jungermanniales.

(i) The thalloid protonema resembles to the juvenile stages of some acrogynous Jungermanniales (e.g. Metzgeriopsis pusilla). The thallus in both the cases grows by the activity of two-sided cell.

(ii) The antheridium of Sphagnum resembles with that of Porella (acrogynous Jungermanniales) in position, development, form and dehiscence. The apical cell discontinues its activity quite early, thus accounting for the shape of antheridium spherical or oblong. The antheridia dehisce into several irregular lobes.

(iii) The archegonium resembles to that of acrogynous Jungermanniales in position, origin and development. There is no differentiation of apical cell in the development of secondary archegonia.

(iv) The spore germination into thalloid protonema exhibits a resembling tendency.

(v) Presence of rudimentary stomata on capsule wall is similar to that of Jungermanniales.

The sporogonia of Sphagnum and members of Anthocerotales show following similarities:

(i) The archesporium develops from amphithecium.

(ii) The whole endothecium changes into columella.

(iii) The capsule body has several chlorophyllose cells.

(iv) The seta is rudimentary.

(v) The foot is bulbous.

(vi) The apical growth is absent.

However, sporogonia of Anthocerotopsida differ from that of Sphagnum in possessing the following features:

(i) True stomata on capsule wall are present.

(ii) Elaters are formed along with the spores.

(iii) Capsule is elongated and cylindrical.

(iv) Capsule does not show any differentiation into annulus and operculum.

(v) The meristematic zone is present in sporogonium.

(i) The gametophores are upright and leafy.

(ii) Rhizoids are obliquely septate.

(iii) The stem, leaves and sex-organs develop by the activity of apical cell.

(iv) The archegonia are provided with a stalk and a massive venter.

(v) The capsule dehisces by a definite operculum.

(vi) Elaters are not formed with spores,

However, Sphagnum differs from the true mosses as follows:

(i) Protonema is thalloid.

(ii) Rhizoids are absent in the adult plant.

(iii) A leaf has two kinds of cells.

(i) The rhizoids are absent in adult gametophyte.

(ii) The branches arise in tufts from the axil of every fourth leaf.

(iii) The leaves lack mid-rib.

(iv) The hyaline cortical cells are found surrounding the inner tissue.

(v) Two special types of leaves are present in plants.

(vi) The plants are hygroscopic and hydrophytes.

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