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In this article we will discuss about:- 1. Habit and Habitat of Sphagnum 2. Special Features of Sphagnum 3. Affinities.
Habit and Habitat of Sphagnum:
Sphagnum is represented by about 336 species which are cosmopolitan in distribution. In India, it is represented by about 20 species in Himalayas. These species are aquatic or semiaquatic and grow in dense masses or cushions in swamps, ponds and lake margins, moist heaths and wet hill sides.
Special Features of Sphagnum:
1. Absence of rhizoids in adult leafy gametophore.
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2. Branches arise in tufts from the axil of every fourth leaf.
3. Absence of mid rib in the leaves.
4. Stem and leaves show unique structures. Cortex in the old stem is spongy and sometimes develops spiral thickenings. Single layered leaf consists two types of cells: large hyaline cells and small green photosynthetic cells.
5. Presence of hyaline retort cells.
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6. The water in which it grows is highly acidic. It is due to the presence of some organic substance of a colloidal nature in the cell walls.
Above resemblance of Sphagnum with Hepaticopsida, Anthocerotopsida and Bryopsida suggest that Sphagnidae may be synthetic group.
Affinities of Sphagnum:
Sphagnum shows resemblance with liverworts (Hepaticopsida), hornworts (Anthocerotopsida) and mosses. However, it possess certain characters in which it stands apart from all the three.
These are:
Resemblance with Hepaticopsida:
(a) Thalloid protonema resemble the juvenile stage of some acrogynous Jungermanniales.
(b) Position, structure and dehiscence of antheridium is like jungermanniales (e.g. Porella)
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(c) Position origin and development of archegonium is similar to that of acrogynous Jungermanniales.
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These resemblances between the liverworts and Sphagnum point to the its intermediate position between the liverworts and mosses.
Resemblance with Anthocerotopsida:
(a) Absence of apical growth in the young sporogonium.
(b) Development of archesporium from the amphithecium which overarch the columella.
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(c) Development of entire endothecium into columella.
(d) Capsule wall possess chloroplast and rudimentary stomata.
(e) Sporogonium is differentiated into bulbous foot, and constriction like seta.
Resemblance with Mosses:
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1. Presence of erect, leafy gametophore.
2. Multicellular, branched rhizoids with oblique septa.
3. Apical growth of stem, leaves and antheridia.
4. Archegonium having massive stalk and venter.
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5. Absence of elaters.
6. Dehiscence of capsule by operculum.
